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INVITED REVIEW

Physiology and pathophysiology of Na⁺/H⁺ exchange and Na⁺-K⁺-2Cl^– cotransport in the heart, brain, and blood

¹Department of Biochemistry, Institute of Molecular Biology and Physiology, University of Copenhagen, Copenhagen, Denmark; and ²Department of Physiology and Membrane Biology, School of Medicine, University of California Davis, Davis, California

	ABSTRACT

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Maintenance of a stable cell volume and intracellular pH is critical for normal cell function. Arguably, two of the most important ion transporters involved in these processes are the Na⁺/H⁺ exchanger isoform 1 (NHE1) and Na⁺-K⁺-2Cl^– cotransporter isoform 1 (NKCC1). Both NHE1 and NKCC1 are stimulated by cell shrinkage and by numerous other stimuli, including a wide range of hormones and growth factors, and for NHE1, intracellular acidification. Both transporters can be important regulators of cell volume, yet their activity also, directly or indirectly, affects the intracellular concentrations of Na⁺, Ca²⁺, Cl^–, K⁺, and H⁺. Conversely, when either transporter responds to a stimulus other than cell shrinkage and when the driving force is directed to promote Na⁺ entry, one consequence may be cell swelling. Thus stimulation of NHE1 and/or NKCC1 by a deviation from homeostasis of a given parameter may regulate that parameter at the expense of compromising others, a coupling that may contribute to irreversible cell damage in a number of pathophysiological conditions. This review addresses the roles of NHE1 and NKCC1 in the cellular responses to physiological and pathophysiological stress. The aim is to provide a comprehensive overview of the mechanisms and consequences of stress-induced stimulation of these transporters with focus on the heart, brain, and blood. The physiological stressors reviewed are metabolic/exercise stress, osmotic stress, and mechanical stress, conditions in which NHE1 and NKCC1 play important physiological roles. With respect to pathophysiology, the focus is on ischemia and severe hypoxia where the roles of NHE1 and NKCC1 have been widely studied yet remain controversial and incompletely elucidated.

ischemia; hypoxia; intracellular pH; intracellular sodium concentration

Maintenance of a low [Na⁺]_i is critical for normal cell function. Under steady-state conditions, [Na⁺]_i is generally maintained below 20 mM, whereas the extracellular Na⁺ concentration ([Na⁺]_o) is 140 mM. This sevenfold concentration difference, together with the negative membrane potential (V_m) constitutes a substantial inward driving force for Na⁺, which is used ubiquitously to drive a wide variety of transport processes.

Cell volume, and/or net intracellular osmolyte concentration plays a pivotal role in a wide range of cellular processes, and consequently must be tightly controlled to maintain normal cell function. Osmotic cell shrinkage, resulting in vivo from either a decrease in intracellular osmolarity or an increase in extracellular osmolarity (106), therefore, generally activates compensatory ion (and osmotically obliged water) uptake, which persists until volume recovery is complete. The most important acutely shrinkage-activated ion transport mechanisms are 1) NHE1 functioning in parallel with a Cl^–/HCO₃^– exchanger (AE), and 2) NKCC1 (106). In most cells, the activity of these transporters leads to a full or partial volume recovery, also known as the process of regulatory volume increase (RVI). Regulation of volume by NHE1 and/or NKCC1 after cell shrinkage can be associated with an incipient increase in [Na⁺]_i, and stimulation of NHE1 or NKCC1 in nonshrunken cells by, e.g., hormones and growth factors, will result in both water and Na⁺ uptake. Yet in healthy cells, [Na⁺]_i is maintained relatively constant because of the activity of the Na⁺-K⁺-ATPase.

Another parameter fundamental to cell function and requiring tight homeostasis is intracellular pH (pH_i) (28, 48). In most mammalian cells, steady-state pH_i is maintained in the range of 7.0–7.2, although this may vary widely (28, 48). Even though extracellular pH (pH_o) is 7.4, given the negative V_m, there is a substantial net inward electrochemical driving force for H⁺ per se. Additionally, metabolic processes create a net cellular H⁺ load, and H⁺ must be actively extruded from the cytoplasm. In most cases, acid-stimulated, H⁺ extruding transporters utilize the inward Na⁺ gradient, the most important players being Na⁺/H⁺ exchange, Na⁺-coupled Cl^–/HCO₃^– exchange, and Na⁺-HCO₃^– cotransport (28). Thus regulation of pH_i after an acid load may increase both [Na⁺]_i and cell volume. On the other hand, stimulation of NHE1 or NKCC1 may lead to changes in pH_i, the magnitude of this effect being dependent on the activity of AE; NHE1 is functionally coupled to AE at a ratio of 1 by changes in pH_i and therefore [HCO₃^–]_i (for a discussion, see Ref. 40). At 1:1 coupling, HCO₃^– influx via AE perfectly buffers H⁺ efflux via NHE1, and NHE1 activity is without effect on pH_i. However, when the activity of NHE1 exceeds that of AE, intracellular alkalinization results (see Ref. 40). Although NKCC1 activity per se is without effect on pH_i, it may be noted that this transporter may be indirectly coupled to pH_i changes through [Cl^–]_i, that is, an increase in [Cl^–]_i causes AE to operate in the direction of recycling Cl^– out of the cell, resulting in HCO₃^– influx and a intracellular alkalinization in cells with a robust AE.

Furthermore, because of the interplay of these transporters with AE and the Na⁺-K⁺-ATPase, stimulation of NHE1, as well as of NKCC1, can affect [Cl^–]_i and [K⁺]_i, both essential modulators of multiple cell functions from effects on V_m and excitability to cell death and proliferation (283, 342). With respect to cations, the eventual result of both NHE1 and NKCC1 stimulation under conditions of optimal Na⁺-K⁺-ATPase activity is increased [K⁺]_i, rather than increased [Na⁺]_i (see Ref. 40). However, as will be discussed below, Na⁺-K⁺-ATPase activity is frequently compromised in stressed cells, such that both NHE1 and NKCC1 can elicit sizable increases in [Na⁺]_i. Finally, whereas either NHE1 coupled with AE, or NKCC1 by itself, can increase [Cl^–]_i, it should be noted that functional coupling of AE with these transporters may have opposite effects on [Cl^–]_i, i.e., 1:1 coupling of NHE1 and AE will tend to increase [Cl^–]_i, whereas 1:1 coupling of NKCC1 with AE is more likely to limit increases in [Cl]_i.

The overall aim of this review is to provide the reader with the knowledge required to appreciate the respective roles of NHE1 and NKCC1 in the detrimental events resulting from ischemia and severe hypoxia in the heart, brain, and blood. Thus we will first (section 2) provide an update on the defining characteristics of these two transporters. This will be followed (section 3) by an overview and comparative analysis of the roles of NHE1 and NKCC1 in the response to a variety of physiological stressors and, finally, (section 4) by an in-depth description of the involvement of NHE1 and NKCC1 in ischemia and severe hypoxia in the heart, brain, and blood, respectively. A brief overview (section 5) of the relatively scarce evidence regarding the roles of NHE1 and NKCC1 in apoptosis and necrosis in ischemia/hypoxia concludes the review.

	2 NHE1 and NKCC1: Defining Characteristics

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2.1 NHE1

2.1.1 Tissue and cellular localization. NHE1 (SLC9A1, Fig. 1A) belongs to the family of Na⁺/H⁺ exchangers of which nine are identified to date (195, 209). NHE1 is expressed in virtually all cell types studied (209, 222, 238) with avian red blood cells (RBCs) as a notable exception in that they lack volume-sensitive Na⁺/H⁺ exchange while exhibiting robust NKCC1 activity (140). In polarized cells, NHE1 is generally located in the basolateral (abluminal) membrane (see Ref. 209). In the microvascular endothelial cells of the blood-brain barrier (BBB), NHE1 appears to contribute to secretion of Na⁺, Cl^–, and water into the brain during ischemia (as discussed in section 4); however, it is as yet unknown whether NHE1 localizes to the luminal or abluminal membrane of the BBB cells (68, 307). At least in some cells, NHE1 localizes to discrete plasma membrane subdomains, examples being the preferential localization to focal adhesions in fibroblasts (97) and to intercalated discs and transverse tubules in cardiomyocytes (227).

View larger version (28K): [in this window] [in a new window]   Fig. 1. Na+/H+ exchanger isoform 1 (NHE1) and Na+-K+-2Cl– cotransporter isoform 1 (NKCC1). Predicted topology and major regions of importance for regulation. A: NHE1 (SLC9A1). PtdIns(4,5)P2, phosphatidyl-inositol(4,5)bisphosphate; CAII, carbonic anhydrase II; PP1, protein phosphatase 1; NIK, Nck-interacting kinase; CHP, calcineurin homolog protein. B: NKCC1 (SLC12A2). SPAK, ste20-related proline- and alanine-rich kinase.

2.1.3 Molecular structure. The NHE1 protein consists of 780–820 amino acids with a calculated molecular mass of 87–91 kDa. Hydropathy analyses in conjunction with studies of protease cleavage and cysteine accessibility support a topology model with 12 transmembrane (TM) domains, a reentrant loop between TM 9 and TM 10, and a long cytoplasmic- COOH-terminal region consisting of about 300 amino acids (272, 320) (Fig. 1A). The mammalian NHE1 contains consensus sites for both N- and O-linked glycosylation in the first extracellular loop, and N-linked glycosylation was proposed to play a role in the basolateral sorting of NHE1 (51). High- resolution structures are not available for the vertebrate NHE1s; however, recent studies of two-dimensional crystals of the Escherichia coli NHE, NhaA, also suggest a 12 TM structure (326). Furthermore, these studies indicated that NhaA may assemble as a dimer (326), which is in agreement with studies of the mammalian NHE1 (104).

The NH₂-terminal domain with the 12 TM regions (500 amino acids) is highly conserved between vertebrate species and is responsible and sufficient for ion translocation by NHE1 (319). The COOH-terminal cytoplasmic domain (300 amino acids) is the main site of regulation of NHE1 function and exhibits a considerable sequence variation between species. This COOH-terminal domain contains binding sites for a large number of ancillary proteins and lipid mediators, primarily in the region closest to the TM domains (Fig. 1A). Although not all of these will be further discussed in this review, it should be mentioned that NHE1 binding partners shown to interact with the COOH-terminal domain include the plasma membrane-cytoskeleton linker ezrin [of the ezrin/radixin/moesin (ERM) protein family], calcineurin homolog protein (CHP), the ste20-related kinase Nck-interacting kinase, protein phosphatase 1 (PP1), calmodulin, carbonic anhydrase, and the phospholipid phosphatidyl-inositol(4,5)bisphosphate. The most COOH-terminal part of this region contains multiple protein kinase consensus sites, the roles of which in NHE1 regulation have been extensively studied (see Refs. 181, 209, 222, and 238).

2.1.4 General physiological roles. By far the best characterized physiological functions of NHE1 are the regulation of cellular volume and pH, although other roles have also been described (see Refs. 209, 221, and 238). After cell shrinkage, rapid NHE1-mediated Na⁺ influx in conjunction with Cl^– influx via the AE restores cell volume, while after intracellular acidification, the NHE1-mediated H⁺ efflux efficiently restores pH_i (see, e.g., Refs. 209 and 222). Under normal physiological conditions, i.e., as long as such deviations from steady state are moderate and transient, this has the effect of normalizing cell volume or pH_i, whereas after dramatic or prolonged deviations from steady-state pH_i or volume, NHE1-mediated effects on [Na⁺]_i and pH_i are important in the cellular damage associated with such conditions, as will be discussed below.

An important aspect of NHE1 regulation is the effect of interactions between different stimuli. In Amphiuma tridactylum RBCs, when stimulated by intracellular acidification, NHE1 remained active until pH_i reached its set point, and was not turned off by the cell swelling resulting from NHE1 activity (40). Conversely, when stimulated by cell shrinkage, NHE1 remained active until cell volume was restored, in spite of a substantial increase in pH_i (40), which, if acting alone, would otherwise deactivate NHE1. Similarly, a wide range of cell culture studies show that after stimuli, such as hormones, growth factors, and inhibitors of ser/ser phosphatases, which activate NHE1 at normal pH_i and volume, the exchanger can remain active in spite of substantially increased cell volume, pH_i, and [Na⁺]_i (224–226, 260, 318). Such increases in cell volume and pH_i may modulate, e.g., cell proliferation (see Ref. 221). This has led to the proposal that increased NHE1 activity is a prerequisite for tumor cell proliferation, a notion which has, however, been disputed by other workers in the field (for a discussion, see Refs. 221 and 274). Again, a detailed discussion of this is beyond the scope of this review, but it should be noted that in recent years, the physiological roles of NHE1 have been suggested to include modulation of, e.g., cell morphology, migration, and invasion (see Refs. 209 and 238). Interestingly, these roles of NHE1 appear in some cases to be at least partly unrelated to ion transport, and rather involving direct interactions of NHE1 with, e.g., ERM proteins (see Ref. 238).

Consistent with the fundamental roles of NHE1 in normal cell function, NHE1 knockout mice exhibit multiple abnormalities, including locomotor problems, growth retardation, abnormal membrane excitability, and Na⁺ permeability of hippocampal CA1 neurons, and 70% of the knockout animals die before weaning (20, 99). On the other hand, these mice exhibit significant protection from ischemic damage in both the heart and the brain (section 4).

2.2 NKCC1

2.2.1 Tissue and cellular localization. The Na⁺-K⁺-2Cl^– cotransporter NKCC1 (SLC12a2, also known as BSC2; Fig. 1B) is expressed in the great majority of cell types studied, whereas the other cloned isoform, NKCC2 (SLC12a1, BSC1), is restricted to the kidney (see Ref. 254). RBCs of certain species, such as teleost fishes and amphibians, however, do not appear to exhibit volume-sensitive Na⁺-K⁺-2Cl^– cotransport, yet exhibit robust NHE activity (37, 108, 141). NKCC1 is found on the basolateral membrane of secretory epithelial cells (254). An exception to this is the microvascular endothelial cells of the BBB, which secrete Na⁺ and Cl^– from the blood into the brain. In this case, NKCC1 is located in the apical (luminal) membrane (205) and secretion (i.e., transport from blood into tissue) occurs in an apical-to-basolateral direction. Also, in the choroid plexus, NKCC1 appears to be located in the apical membrane (235).

2.2.2 Energetics, kinetics, and control. The driving force for Na⁺-K⁺-2Cl^– cotransport via NKCC1 is µ(Na⁺ + K^– + 2Cl^–) = µNa⁺ + µK⁺ + 2 µCl^– = RT·ln ([Na⁺]_i/[Na⁺]_o) + RT·ln ([K⁺]_i/[K⁺]_o) + 2{RT·ln ([Cl^–]_i/[Cl^–]_o)} = RT·ln ([Na⁺]_i·[K⁺]_i·[Cl^–]_i²)/ ([Na⁺]_o·[K⁺]_o·[Cl^–]_o²). Under normal physiological conditions, the outwardly directed K⁺ gradient tends to be slightly greater than the inwardly directed Na⁺ gradient, such that [Cl^–]_i becomes an important determinant of the direction of transport via NKCC1. In most cells, the direction of transport will be inward, although near-equilibrium situations are found in some cells (254). After a few minutes of ischemia-induced NHE1-mediated Na⁺ accumulation, however, the driving force for transport via NKCC1 may, in some cases, be directed out of the cell (7, 150). In RBCs, outward transport by NKCC1 has been proposed to contribute to the cell shrinkage involved in reticulocyte maturation (section 3.3.2). Increased NKCC1 activity is associated with, and appears to be dependent on, an increase in the direct phosphorylation of NKCC1 on ser and thr residues (see Refs. 78, 101, and 254). Only a few studies have addressed the molecular mechanism of altered transport rates via NKCC1 on regulation. Studies in intestinal epithelial cells have suggested that at least in some cases, regulation of Na⁺-K⁺-2Cl^– cotransporter activity is associated with a change in the number of transporters in the plasma membrane, i.e., an effect on V_max, rather than on substrate affinity (83, 170). On the other hand, in HeLa cells, ATP depletion reduced NKCC1 activity with no effect on V_max but with reduced affinity for extracellular Rb⁺ (116).

2.2.3 Molecular structure. The NKCC1 protein consists of about 1,200 amino acids and has a calculated molecular mass of about 130 kDa (see Refs. 101 and 254). On the basis of hydropathy analyses, a membrane topology of 12 central TM domains and cytosolic NH₂- and COOH-terminal regions has been proposed (88) (Fig. 1B). NKCC1 contains two N-linked glycosylation sites in the fourth extracellular loop. Both the NH₂- and COOH-terminal cytosolic domains contain protein kinase consensus sites, and, in addition, the NH₂-terminal cytosolic domain has been shown to bind PP1 (57) and the ste20-related proline- and alanine-rich kinase (SPAK) (231; see Fig. 1B). NKCC1 has been proposed to form homodimers, although a functional role for this has yet to be established (184). The highest degree of conservation between species is found in the central TM and COOH-terminal regions, although three consensus sites for thr phosphorylation in the NH₂-terminal region are conserved across a broad range of species (see Refs. 101 and 254).

2.2.4 General physiological roles. NKCC1 is stimulated by a wide range of hormones and growth factors, as well as by osmotic shrinkage (161, 192; see also Refs. 78 and 254), laminar stress (296), and hypoxia or deoxygenation (79, 81, 131, 192). In contrast to the marked stimulation of NHE1 in response to acidic pH_i, NKCC1 is inhibited at pH_i values below 7.0 (215, see also Ref. 254). The most well-defined physiological roles of NKCC1 are in the regulation of [Cl^–]_i, epithelial Cl^– secretion, and cell volume (see Ref. 254). NKCC1 is stimulated by osmotic shrinkage in most cell types studied, and, if the prevailing ion gradients permit, NKCC1 can and does play an important role in the RVI process (see Ref. 254). Studies in epithelial and nonepithelial cell types have indicated that NKCC1 plays a major role as a Cl^– influx pathway maintaining [Cl^–]_i above equilibrium, i.e., the equilibrium potential for Cl^– more positive than V_m (5, 95). Moreover, astrocytes from NKCC1 knockout mice exhibited reduced basal [Na⁺]_i, suggesting a role for NKCC1 in regulating basal astrocyte [Na⁺]_i (289). Vectorial NaCl transport in secretory epithelia is dependent on the functional coupling of the basolaterally located NKCC1 to apical Cl^– channels, basolateral K⁺ channels and the Na⁺-K⁺-ATPase (e.g., Ref. 95). In the BBB, NKCC1 may function in vectorial transport of NaCl from blood into brain, and as discussed below, increased NKCC1 activity in the BBB contributes to cerebral edema formation in ischemia (81, 203, 205). A role for NKCC1 in regulation of cell proliferation has also been proposed, although this is less well established (see Ref. 254).

Consistent with the proposed major physiological roles of NKCC1, the phenotype of NKCC1 knockout mice includes deafness, imbalance (Shaker/Waltzer phenotype), and decreased Cl^– secretion in e.g., intestine and trachea (60, 77). However, as will be discussed in section 4, they also exhibit less brain damage in experimental stroke (47).

	3 NHE1 and NKCC1 in the Response to Physiological Stress

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As described above, NHE1 and NKCC1 play important roles in reestablishing homeostasis after physiological perturbations to cell volume, pH_i, and [Cl^–]_i, and in the adaptive responses to a variety of physiological stressors. We define physiological stress in broad terms as the stimuli to which cells are exposed under normal physiological conditions, resulting in temporary deviations from the steady state. The relevant physiological stressors are obviously numerous and will depend on the species and cell type, but for the purpose of the present review, we focus on three major categories: metabolic and exercise stress, osmotic stress, and mechanical stress. All of these conditions, if sufficiently severe, may of course become pathophysiological; for instance, the ability of severe hypertonic stress to elicit cell death is well established (29, 36, 201).

Metabolic stress in the form of a reduced cellular ATP level may result from, e.g., exercise stress, mild hypoxia, or reduced availability of nutrients, and is typically associated with reduced pH_i, as well as with changes in the cellular level of reactive oxygen species (ROS). Exercise stress exhibits several similarities with hypoxic stress at the level of plasma hormone and ion concentrations. In mammals, vigorous exercise is associated with reductions in microvascular oxygen pressure (PO₂) (19, 125). Also similar to hypoxic conditions, exercise is associated with catecholamine release and increased plasma catecholamine levels, with elevated plasma [K⁺] because of substantial K⁺ loss from skeletal muscle, and with plasma acidification (see, e.g., Refs. 153 and 172).

The ability of cells to regulate their volume is highly conserved and often involves multiple osmolyte transport mechanisms, reflecting the fundamental importance of cell volume for cell function (see Ref. 106). As noted above, after acute osmotic shrinkage, some, yet not all, cell types are capable of regulating their volume in the process of RVI, and NHE1 and NKCC1 are the most common mediators of this process (107, 209, 254). Most of the cells in the body are not exposed to major changes in extracellular osmolarity under physiological conditions. Of the tissues of interest in this review, RBCs are, however, an important exception, as they are exposed to a major hypertonic challenge on their way through the kidneys (see Ref. 106). Much more common are changes in epithelial cell volume resulting from changes in intracellular solute concentration, e.g., after secretion/absorption, and exercise- or hormone-mediated metabolic changes (see Ref. 106). Notably, therefore, metabolic and osmotic stress are in some cases functionally coupled. Similarly, mechanical stress (see below) elicits ion channel activation (e.g., Refs. 34 and 296), resulting in osmolyte loss and therefore cell shrinkage.

Mechanical stress in the form of, e.g., stretch or fluid shear stress is experienced by many cell types. Cardiac myocytes, cardiac and brain endothelial cells, and RBCs are exposed to mechanical stress under physiological conditions (245, 256, 287), and neurons and glial cells can also experience a range of mechanical stresses, ranging from physiological mechanical stimuli to traumatic brain injury (160). Mechanical stress elicits a wide range of signaling events, including activation of integrins and growth factor receptors, G protein activation, cytoskeletal rearrangement, ATP and ROS release, increases in [Ca²⁺]_i, and activation of mitogen-activated protein kinases (MAPKs) and other protein kinases. These events, in turn, elicit both acute activation of ion transporters, and activation of transcription factors eliciting the induction of genes involved in controlling, e.g., cell growth, morphology, and ion transport (213, 220, 296; see also Ref. 76).

Tables 1 and 2 summarize the localization and major physiological roles of NHE1 and NKCC1, respectively, in the heart, brain, and blood. In the following sections, these roles will be described, in turn, for those stimuli for which evidence is available in the tissue in question.

The heart depends primarily on aerobic metabolism under physiological conditions, yet ATP produced through the glycolytic pathway appears to be necessary for some cardiac functions, including Na⁺ homeostasis (42). The proportion of ATP produced glycolytically is further increased during exercise and other physiological conditions of increased energy demand, leading to an increased requirement for H⁺ extrusion (42, 92). Cell volume perturbations in the heart occur predominantly under pathophysiological conditions, such as diabetic coma, septic shock, or ischemia (327). Hypertonic cell shrinkage negatively affects cardiac contractility, and hypotonic swelling shortens the cardiac action potential (110, 327). In spite of these severe consequences of cardiomyocyte volume perturbations, the extent to which cardiomyocytes are able to volume regulate is a controversial issue, with most studies concluding that these cells do not perform RVI (206, 327). Shrinkage-induced stimulation of both NHE1 and NKCC1 has, however, been reported in the heart, as will be discussed below.

3.1.1 Roles of NHE1. NHE1 appears to be the only, or by far, the predominant NHE isoform in cardiac myocytes (80, 210, 310), where it has been shown to localize mostly to the transverse tubules and intercalated disc regions (227). Consistent with the high demand for metabolic acid extrusion under steady-state conditions in the heart, the myocardial NHE1 exhibits high tonic activity and plays a major role in cardiac pH_i homeostasis under physiological conditions (80). In congruence with the proposed importance of glycolytically derived ATP for cardiac Na⁺ homeostasis (42), NHE1 has been proposed to be specifically dependent on ATP produced by glycolysis rather than by oxidative phosphorylation (291). This linkage has interesting implications, because NHE1 stimulation may be preferentially coupled to ATP produced under conditions (i.e., increased glycolysis) that necessitate increased H⁺ extrusion.

As in most cell types, NHE1 is also stimulated by hypertonic stress in both mature and neonatal cardiac myocytes (183, 325). This may, however, not lead to an RVI response, as it has been suggested that mature cardiomyocytes cannot perform RVI (327).

NHE1 plays an important role in the physiological events elicited in the heart by mechanical stress in the form of cell stretch. In isolated rabbit myocardium, the slow force response component of the muscle stretch response was dependent on stretch-induced NHE1 activation, followed by increased cytosolic [Na⁺] and increased [Ca²⁺]_i because of Na⁺/Ca²⁺ exchanger (NCX) reversal (316). Similar findings have been reported in other cardiomyocyte preparations (333). Interestingly, stimulation of NHE1 by cardiomyocyte stretch has been found to be upstream of stretch-induced Raf-1 and MAPK activation and subsequent hypertrophy (299, 333).

3.1.2 Roles of NKCC1. Evidence for the presence of NKCC1 in whole mammalian hearts, as well as in isolated ventricular myocytes, has been obtained both at the functional level (7, 65, 252) and at the mRNA and protein level (6, 241, 314). NKCC1 has also been characterized in aortic endothelial cells (341). Compared with the abundant literature on NHE1, relatively little is known about the roles and regulation of NKCC1 in the heart. NKCC1 likely plays a role in maintaining cardiac resting [Na⁺]_i and [Cl^–]_i (84, 114), yet we are not aware of direct studies of the effects of physiological metabolic stress on NKCC1 in the heart.

A role for NKCC1 in isotonic and anisotonic cell volume regulation has been proposed in rabbit ventricular myocytes (65) and in smooth muscle cells from rat aorta (208). Yet, others failed to find detectable NKCC1 activity after hypertonic stress in the heart (71). NKCC1 is also stimulated by osmotic shrinkage of aortic endothelial cells in which RVI was inhibited by bumetanide (202). The RVI was, however, not complete by 30 min, suggesting that complete RVI is a slow process or that the cells are unable to completely recover (202). In other studies, an RVI response could not be demonstrated in aortic endothelial cells (see Ref. 206). Finally, in bovine aortic endothelial cells, mechanical stress in the form of steady laminar shear stress activated and upregulated NKCC1, an effect that was shown to involve shear stress-induced activation of K⁺ and Cl^– channels (296).

3.2 Physiological Stress in the Brain

In the brain, metabolic stress requiring regulation of pH_i occurs under physiological conditions, because both neurons and glial cells undergo significant shifts in pH_i during increased neuronal activity. For instance, in cultured hippocampal neurons (322) and brain stem slices (308), depolarizing stimuli were shown to elicit intracellular acidification. This decrease in pH_i is, at least in part, dependent on Ca²⁺ entry and in vertebrate neurons appears to mainly reflect metabolic acid production (322, 344). Additionally, because of its permeability to HCO₃^–, activation of the GABA_A receptor also decreases pH_i, as shown in both cultured astrocytes (126) and acutely isolated hippocampal neurons (219).

Under physiological conditions, the volume of both neurons and glial cells is constantly challenged by the transmembrane ion movements occurring during normal neuronal activity, and these volume changes may, in turn, affect brain function (163, 218, 283). Brain volume regulation, associated with net cellular uptake of Na⁺, K⁺, Cl^–, and water, and a concomitant reduction in extracellular volume, has been measured in vivo in rats exposed to acute hypernatremia (54). Glial cells are capable of cell volume regulation after acute osmotic swelling and shrinkage (69, 175). With respect to neurons, this is more controversial; in several neuronal preparations, no volume regulation could be detected after acute osmotic stress (2, 11), and it appears that more severe (nonphysiological) osmotic challenges are required for neurons to be capable of acute RVI (see e.g., Ref. 53). On the other hand, immature cortical neurons exhibited RVI after a relatively modest increase in extracellular osmolarity (265).

3.2.1 Roles of NHE1. NHE1 is widely expressed in the central nervous system (CNS) and is the most abundant NHE isoform in the cerebral cortex (162, 210). Na⁺/H⁺ exchange activity has been found in virtually all neuronal and glial cell types studied, although it was not always unequivocally established whether the isoform in question was NHE1 (48). This is an important question, since NHE2, NHE3, NHE4, and NHE5 are also found in the brain, although with more restricted patterns of distribution (48). NHE1 message has also been detected in choroid plexus (127; Praetorius J, personal communication), which is known to exhibit amiloride-sensitive Na⁺/H⁺ exchange (191). Finally, message for NHE1 (and also for NHE2, NHE3, and NHE4) was detected in BBB endothelial cells (68, 127, 281, 281, 315), and there is evidence that NHE1 is an important mediator of steady-state Na⁺ transport across the BBB (68).

NHE1 plays a key role in pH_i regulation in both neurons and glial cells under steady-state conditions and after intracellular acidification (48, 162, 173, 212, 223). Recovery of pH_i after metabolic acid production associated with neuronal activity (see section 3.2) appears to be a major function of NHE1 in brain neurons. Consistent with this view, both acutely dissociated CA1 pyramidal neurons from NHE1 null mice (339) and astrocytes from NHE1 null mice (137) exhibit reduced steady-state pH_i, as well as reduced or virtually absent H⁺ extrusion after intracellular acidification. Shrinkage-induced NHE1 stimulation has been demonstrated in primary rat astrocytes (273). No studies have, to our knowledge, directly demonstrated osmotically induced NHE1 activity in neurons, neither in the intact brain nor in culture.

3.2.2 Roles of NKCC1. NKCC1 mRNA has been detected in choroid plexus, cerebellum, brainstem, and to a lesser extent, cerebral cortex and hypothalamus (128, 235), reflecting NKCC1 expression in a wide range of neuronal cell types (129, 235), in glial cells (oligodendrocytes and astrocytes) in various regions of the brain (128, 150, 205, 323, 335), and in cerebral microvascular endothelial cells (203, 205, 292, 293). In the latter, functional and immunocytochemical evidence indicated the presence of NKCC1 in the luminal membrane (202, 205), although others have failed to detect brain microvessel NKCC1 mRNA in in situ hybridization studies (235). Interestingly, in the choroid plexus epithelium, NKCC1 is extremely abundant and is only expressed on the apical membrane (235).

The main physiological roles of NKCC1 in the brain appear to be 1) the regulation of [Cl^–]_i and thus, -aminobutyric (GABA)-ergic signaling (GABA being excitatory at high [Cl^–]_i, and inhibitory at low [Cl^–]_i) (59, 295); 2) ion transport across the BBB (81, 203, 205) and choroid plexus (330); and 3) although this is less well established, in cell volume regulation (see below). A role in regulating basal [Na⁺]_i has also been suggested, based on studies of NKCC1^–/– astrocytes (289).

NKCC1 expression is high in immature neurons and decreases with maturation, whereas the inverse is true for the K⁺-Cl^– cotransporter KCC2 (see Ref. 59). These changes are thought to underlie the decrease in neuronal [Cl^–]_i during development and the shift from excitatory to inhibitory GABA signaling (see Ref. 59). NKCC1 still contributes to regulation of [Cl^–]_i in adult neurons, some of which, including, e.g., dorsal root ganglion neurons, exhibit a high NKCC1 expression, high [Cl^–]_i, and depolarizing responses to GABA (see Ref. 59).

In neurons capable of cell volume regulation after osmotic shrinkage, NKCC1 may play a role in this process. In immature cortical neurons, NKCC1 was activated by osmotic shrinkage, and a bumetanide-sensitive RVI was demonstrated (265). Osmotically induced Na⁺-K⁺-2Cl^– cotransport was also observed in squid giant axons (32) and in PC12 cells (151). In C6 glioma cells, NKCC1 appears to be important in both isotonic volume homeostasis and RVI (45, 175). Similarly, RVI was robust in wild-type (NKCC1^+/+) astrocytes, but absent in NKCC1^–/– astrocytes (289). NKCC1 is also stimulated by osmotic shrinkage in cerebral microvascular endothelial cells, although it is not yet known whether this translates into an RVI response in these cells (202).

3.3 Physiological Stress in the Blood

Exercise stress increases [K⁺]_i, [Na⁺]_i, and [Cl^–]_i in human RBCs (153, 172), and as will be discussed below, in some species, RBCs may play a role in buffering plasma K⁺, at least during high-intensity exercise (153). RBCs from teleost fishes have been extensively used as models for mild hypoxic stress, given the often extremely high exercise level of these species, frequent exposure to hypoxic conditions, and unique requirement for adaptation to large changes in PO₂, as well as the fact that teleost RBCs are nucleated cells with protein synthesis, mitochondria, etc., resembling those of mammalian non-RBC cells (e.g., Refs. 49 and 198). One general finding, pioneered in studies in RBCs from teleosts and other lower vertebrates, and confirmed in some mammalian RBCs, is that a number of ion transporters including, yet not limited to, NHE1 and NKCC1, exhibit marked O₂ dependence (64; see Ref. 89). A role for hemoglobin (Hb) as an O₂ sensor was suggested (89, 186); however, findings in trout hepatocytes indicate that this phenomenon is not limited to RBCs (311). A link with cell volume is suggested in that swelling-activated transporters are generally found to be stimulated, and shrinkage-activated transporters to be inhibited, by a decrease in O₂ pressure (PO₂) (see Ref. 89).

3.3.1 Roles of NHE1. NHE1 appears to be the only NHE isoform in mammalian RBCs (e.g., Ref. 259). Although NHE1 transport capacity decreases with RBC maturation (41) and is modest in most mammalian RBCs, including those of humans, NHE1 is present and functional in mature RBCs from many mammals, including dogs (216), rabbits (123), and humans (30). Moreover, many nucleated RBCs, such as those of teleosts (167, 225) and amphibians (174), exhibit robust NHE1¹ activity. In RBCs from both mammals and lower vertebrates, NHE1 is activated by acidic pH_i, as well as by osmotic shrinkage (37, 123, 269). While RBCs are the focus here, it should be noted that NHE1 is also the predominant or only NHE isoform in platelets and at least some types of leukocytes, in which it has been assigned important physiological roles (85, 96, 247).

Exercise stress elicits an increase in circulating catecholamines in teleosts, resulting in stimulation of NHE1, and, consequently, increased RBC pH_i and cell volume (159), similar to what occurs in hypoxia (see section 4.1) or after direct -adrenergic stimulation (225; see 222). In exercise-stressed human RBCs, increased Na⁺/Li⁺ countertransport following exercise stress has been described (1); however, the possible identity of this transporter with NHE1 is controversial (207).

In RBCs of teleosts and some amphibians, NHE1/-NHE is stimulated under hypoxic conditions, by norepinephrine (NE) via -adrenergic receptors (-ARs), via decreased pH_i, and via a still poorly understood deoxygenation effect on the RBC NHE1 (see Refs. 89 and 222). The physiological consequence is that in response to hypoxic or exercise stress, the O₂ affinity of Hb is increased because of a combination of the NHE-mediated limitation of intracellular acidification, and dilution of Hb resulting from cell swelling (see Ref. 222). To the knowledge of the authors, no such studies exist for NHE1 in higher vertebrates, which, as discussed by Nikinmaa (197), generally have Hbs with lower Bohr/Haldane effects and employ different strategies for optimizing RBC O₂ transport properties.

Osmotic stress potently stimulates NHE1 in RBCs from a wide variety of species, with the interesting exception of some teleosts (see Ref. 222). The first demonstration of the role of Na⁺/H⁺ exchange functionally coupled to Cl^–/HCO₃^– exchange in RVI came from studies of A. tridactylum RBCs in our laboratory (37). This is now known to be a general strategy for RVI in a wide variety of cell types across the vertebrate phylum (106, 222), and the Amphiuma Na⁺/H⁺ exchanger has been cloned and found to be an NHE1 with high homology to mammalian NHE1s (174).

3.3.2 Roles of NKCC1. There is functional evidence for the presence of NKCC1 in RBCs from birds (161), as well as from mammals, including humans (79, 153, 165). Similar to NHE1 in teleost RBCs, NKCC1 in avian RBCs is stimulated by hypoxia and metabolic stress, by virtue of its potent stimulation both by -adrenergic stimuli and by deoxygenation per se (161, 192). As discussed by Gibson et al. (89), the driving force for inward transport via NKCC1 in RBCs is markedly increased by even slight elevations of plasma [K⁺], and a role for NKCC1 as a dynamic buffer for plasma [K⁺] is conceivable. This may play a role in birds (158), which exhibit robust NKCC1 activity and experience extreme exercise stress during migratory flight, but also in mammals with high hematocrits, such as the horse (see Ref. 89). In humans, RBC K⁺ content is also elevated during exercise; however, this appears to be primarily mediated by the Na⁺-K⁺-ATPase, with little, if any, contributions from NKCC1, except under conditions when the Na⁺-K⁺-ATPase is inhibited (153). NKCC1 is also activated by osmotic cell shrinkage in both avian (161) and mammalian RBCs (165). It is interesting to note that as rat RBCs mature, the net driving force for NKCC1 changes direction, being inward in reticulocytes, yet outward in mature RBCs. This net outward transport by NKCC1 may under some conditions contribute to reducing the isotonic volume of the RBCs (166; see also Refs. 158 and 165).

Finally, it may be noted that NKCC1 has also been found in leukocytes, in which it has been proposed to play a role in regulation of MAPK activity and proliferation (214).

	4 NHE1 and NKCC1 in Pathophysiological Stress: Ischemia and Severe Hypoxia

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Under certain pathological conditions, stimulation of NHE1 or NKCC1 does not, as in the examples described in the previous sections, lead to restoration of homeostasis, but rather contributes significantly to the cellular damage resulting from these conditions. Of these, ischemia (severely reduced perfusion or blood flow), and severe hypoxia (including anoxia, i.e., zero or essentially zero oxygen supply, and prolonged hypoxia) are by far the most studied with respect to the roles of NHE1 and NKCC1, yet many open questions and controversies remain. Some of the apparently conflicting findings are likely to reflect differences in experimental protocols. For instance, studies of ischemia have employed either only ischemia or ischemia/reperfusion protocols and with greatly varying exposure times. Moreover, with respect to studying hypoxia at the cellular level, various labs have used either chemical "hypoxia" (such as oligomycine or azide) in the presence of oxygen or various degrees of true hypoxia, with or without glucose, differences that can elicit very different responses. Finally, at least in the brain, the majority of "hypoxia" studies have actually evaluated the in vitro effects of oxygen-glucose deprivation (OGD).

4.1 Ischemia and Severe Hypoxia in the Heart

4.1.1 General Aspects
4.1.1.1 Energy status and ion homeostasis. Ischemia is associated with a marked decrease in the cellular ATP level in the heart (see Ref. 42). It should be noted that the reported rates of decline of ATP levels in ischemic perfused hearts vary considerably, from about one-third reduction within 45 min in ferret hearts (66) to about 50% reduction within 15–20 min in rat hearts (243, 298). Such differences in ATP levels are likely to be due, at least in part, to differences in experimental protocol (see Ref. 4) and may well account for some of the controversy discussed below regarding transporter regulation (sections 4.1.2 and 4.1.3).

The Na⁺-K⁺-ATPase has generally been assumed to be inhibited in ischemia because of ATP-depletion, a notion that has been confirmed in several models of ischemia in the heart (52, 98, 285). Consequently, the ischemia-induced increase in [Na⁺]_i in the heart was originally thought to reflect inhibition of the Na⁺-K⁺-ATPase (98, 285). On the other hand, others have found no evidence of Na⁺-K⁺-ATPase inhibition in early ischemia (237), and more recent studies in perfused rabbit hearts have indicated that in early ischemia, Na⁺-K⁺-ATPase activity is actually increased rather than decreased, presumably as a consequence of the increases in [Na⁺]_i and [K⁺]_o (7). As will be detailed below, the ischemia-induced increases in [Na⁺]_i and [Ca²⁺]_i (10, 271; see also Refs. 189 and 284) are now known to largely reflect stimulation of NHE1 and consequent uptake of Ca²⁺ via the NCX in response to increases in [Na]_i. In agreement with the notion that NCX reversal/equilibrium plays an important role in the ischemia/reperfusion-mediated increase in [Ca²⁺]_i in the heart (268), NCX has been shown to be near or at thermodynamic equilibrium during ischemia (for a discussion, see Ref. 8), indicating that it is a major Ca²⁺ influx pathway under these conditions. Increases in [Cl^–]_i during ischemia have also been demonstrated in the heart (242). Ischemia, moreover, elicits cardiac cell swelling, because of a combination of net inward ion transport and lactate production by anaerobic glycolysis (13, 327). Cardiac pH homeostasis is also severely compromised by ischemia. On exposure to ischemic conditions, pH_o in the heart reaches about 6–6.5, and pH_i falls rapidly, by about 0.5 pH unit in the first 5 min (155, 261, 286).

4.1.1.2 Signaling events. Myocardial ischemia activates the sympathetic nervous system and leads to local release of the catecholamine NE in the ischemic heart (267). In early cardiac ischemia and under normal physiological conditions, NE release is exocytotic and Ca²⁺ dependent, whereas in prolonged ischemia it is carrier mediated and reflects reversal of the driving force for the NE transporter (NET) (152). The renin-angiotensin system also is activated in ischemic hearts, resulting in increased local angiotensin (ANG II) formation. Consistent with a role for ANG II in ischemic damage, ANG II type 1 (AT₁) receptor blockade reduces cardiac damage after ischemia, by mechanisms which are not fully elucidated (115, 122). Endothelin-1 (ET-1) contributes to myocardial damage in ischemia (see Refs. 133 and 297), and at least some of the cardiac effects of ANG II are mediated by ET-1 (185). Local thrombin levels are elevated in intracoronary thrombosis, the most frequent cause of acute myocardial ischemia (58). Finally, cytokines and inflammatory mediators play an important role in myocardial ischemia, in which neutrophil accumulation occurs, at least in part, as a result of increased IL-8 production and contributes to ischemic damage (82).

MAPKs, including extracellular signal-regulated kinase (ERK1/2) and the stress-activated kinases p38 MAPK and c-Jun NH₂-terminal kinase (JNK) are important intracellular mediators after cardiac hypoxia and ischemia/reperfusion (12). There are some discrepancies as to whether these kinases are active in both ischemia and reperfusion. In some studies, ERK1/2 appears to be inhibited rather than activated in ischemia, and only activated on subsequent reperfusion (182; see Ref. 12). The ERK1/2 effector p90 ribosomal S kinase (p90RSK) has been found to be activated in the heart during both ischemia and reperfusion (182). Other classes of protein kinases are also implicated, for instance, there is evidence that at least some of the effects of G protein-coupled receptor agonists in cardiac ischemia, including catecholamines (acting via ₁-ARs), ANG II, ET-1, and thrombin, are mediated via protein kinase C (PKC) (14).

Finally, reperfusion after ischemia/hypoxia is associated with release of ROS, for which a major role has been clearly established in the ensuing cell damage (91, 164). Notably, ROS are also released during hypoxia per se and may be an important signal in hypoxia sensing (102).

4.1.2 Mechanisms and Consequences of Stimulation of NHE1 From studies in isolated cardiac myocytes, perfused hearts, and in vivo models, it is widely acknowledged that NHE1 inhibitors exert protection against myocardial ischemic/hypoxic damage (138, 145, 155, 190, 286, 324). The essential role of NHE1 inhibition in cardiac protection was initially challenged by the fact that amiloride and amiloride derivatives also exert a varying inhibitory effect on Na⁺ channels (46) and on NCX (276). The finding that mice with an NHE1 null mutation are protected from myocardial ischemic damage (324) mitigates this concern. However, although a detailed description of this is beyond the scope of the present review, it should be kept in mind that noninactivating Na⁺ channels, Na⁺-HCO₃^– cotransport, in some cells NKCC1 (section 4.1.3), and at least in late ischemia Na⁺-K⁺-ATPase inhibition, also have been found to contribute to cardiac ischemic damage (52, 132, 176, 312).

A controversy has been whether NHE1 is active during the ischemic phase, and consequently whether NHE1 inhibitors need to be present throughout ischemia/reperfusion, or in the reperfusion phase only, to be effective (4, 189). Thus some studies have shown that although [Na⁺]_i rose during the subsequent reperfusion phase, there was no or only a very small increase in [Na⁺]_i during ischemia, suggesting that NHE1 is inhibited during this phase (182, 331). In contrast, numerous other studies have documented an immediate, robust increase in [Na⁺]_i during ischemia and have concluded that NHE1 is active during both ischemia and reperfusion, although generally most active in the latter (155, 190, 232, 324; see also Ref. 189). Since pH_o rapidly falls to 6–6.5 in ischemic hearts (see section 4.1.1.1 [EC] ), inhibition of NHE1 during the ischemic phase has been proposed to result from competition between Na⁺_o and H⁺_o for NHE1 binding (149). However, at the very acidic pH_i which is prevalent in ischemic hearts, NHE1 is only modestly inhibited by acidic pH_o (313; see also Ref. 4). NHE1 has a high effective half-maximal ATP concentration (2–5 mM) (43, 61) and has, accordingly, been found to be inhibited by the reduced ATP levels associated with metabolic inhibition (43, 329). Because the reported rate of decline of ATP levels in ischemic hearts varies considerably (see section 4.1.1.1 [EC] ), differences in ATP levels, in part, the result of differences in experimental protocol (see Ref. 4), undoubtedly account for some, if not all, of the controversy with regard to the activity of NHE1 during ischemia.

4.1.2.1 Mechanisms of stimulation of NHE1. Figure 2 summarizes major pathways of NHE1 regulation in ischemia/hypoxia. A major stimulus for maintaining high NHE1 activity during ischemia/reperfusion is the decreased pH_i. Consistent with this notion, the rate and pharmacological profile of Na⁺ uptake during hypoxia and during NH₄Cl-induced acidification were similar in perfused rabbit hearts (10). In addition to pH_i, many other mechanisms have been reported to modulate cardiac NHE1 activity during ischemia and severe hypoxia. In the mammalian heart, NHE1 is activated by catecholamines, such as NE via ₁-ARs (146, 321), possibly the ₁A-subtype (see Ref. 14). Consistent with the postulate that ₁-AR-mediated NHE1 activation is a central event in NE-mediated myocardial ischemic damage, NHE1 inhibition reversed the proarrhythmic effect of an ₁-agonist in isolated rat hearts (340). With respect to the -ARs, the picture is less clear, since both inhibition (146) and stimulation (67) of NHE1 in response to stimulation of ₁-AR have been reported.

View larger version (29K): [in this window] [in a new window]   Fig. 2. Major mechanisms and consequences of ischemia/hypoxia-induced activation of NHE1 in a cardiomyocyte. NO, nitric oxide; ET-1, endothelin 1; PKC, protein kinase C; ERK1/2, extracellular signal-regulated kinase 1/2; ROS, reactive oxygen species; NCX, Na+/Ca2+ exchanger; ANG II, angiotensin II.

ERK1/2 and/or the downstream effector p90RSK have been found to be involved in the stimulation of NHE1 by ischemia/reperfusion (182, 258). Supporting this notion, cardiac NHE1 stimulation by _1A-AR agonists, AT₁, and thrombin were attenuated by blocking the ERK1/2 pathway (see Ref. 14). In rat hearts exposed to 30-min of no-flow ischemia and 30-min reperfusion, NHE1 was proposed to be directly phosphorylated by ERK1 following reperfusion, and by p90RSK during both ischemia and reperfusion (182). In contrast, p38 MAPK was found to negatively regulate NHE1 activity after ANG II stimulation in vascular smooth muscle (143).

Not only MAPKs, but also PKC, is implicated in stimulation of NHE1 by cardiac ischemia/hypoxia (243), as well as by a number of G protein-coupled, receptor-mediated signaling events characteristic of cardiac ischemia, including catecholamines (acting via ₁-ARs), ANG II, ET-1, and thrombin (14).

Finally, several studies (194, 249, 258) have implicated ROS (specifically H₂O₂) as important mediators of NHE1 stimulation by cardiac ischemia/reperfusion, in some cases, via ROS-mediated ERK1/2 activation (249, 258).

A number of ischemia-associated signaling events have also been found to attenuate NHE1 activity. Estrogen stimulates the release of nitric oxide (NO), a mechanism suggested to underlie the protection of premenopausal women against myocardial ischemia (200). Recent evidence indicates that the protective effect of NO in cardiac ischemia, at least in part, involves inhibition of NHE1, an effect tentatively suggested to involve cGMP-dependent kinase (PKG) and p38 MAPK (8, 119). Histamine, acting via H₃ receptors, which are inhibitory receptors in cardiac adrenergic nerve endings, was also found to inhibit NHE1, and this was proposed to be the mechanism of H₃-mediated protection in myocardial ischemia (280). Interestingly, hypertonic pretreatment appears to attenuate NHE1 activity and exert protection during hypoxia/ischemia (71, 105). This is consistent with the notion that signaling is prioritized, such that when responding to a given stimulus (in this case cell volume), NHE1 will no longer respond to a second stimulus (in this case acidic pH_i; see section 2.4.1).

4.1.2.2 Consequences of stimulation of NHE1. Figure 2 illustrates some of the major consequences of NHE1 stimulation by cardiac ischemia/hypoxia. Elevated [Ca²⁺]_i is generally considered the major cause of cell damage associated with myocardial ischemia (284). In 1985, Lazdunski and coworkers (149) proposed the "coupled exchanger" hypothesis, which stated that the ischemia-induced increase in [Ca²⁺]_i results from influx, or decreased efflux, of Ca²⁺ via NCX as a consequence of the increase in [Na⁺]_i resulting from increased Na uptake via NHE. The Lazdunski model, based on cells in culture, has since been confirmed and extended by multiple workers in the field (10, 39, 117, 155, 190, 286; see Ref. 264). Among these, the authors of this review have verified the model in both ischemia/reperfusion (7, 155, 156) and in hypoxia (10, 38, 39). In perfused hearts, NHE1 inhibitors attenuate the increases in [Na⁺]_i and [Ca²⁺]_i during ischemia, and improve [Na⁺]_i and [Ca²⁺]_i recovery on reperfusion (155, 286). Moreover, in rat hearts, an inverse correlation between Na⁺ accumulation during ischemia and functional recovery on reperfusion was demonstrated, and Na⁺ recovery on reperfusion was shown to be attenuated by low [Ca²⁺]_o or NCX inhibition (117). This led to the conclusion that NCX-mediated exchange of Ca²⁺_o for Na⁺_i during ischemia is a major mechanism of Ca²⁺ accumulation associated with reperfusion injury (117; see Fig. 2).

The role of pH_i in the downstream events after stress-induced NHE1 activation is a complex issue. Recovery of pH_i on reperfusion is attenuated by NHE1 inhibition in some (261, 286), although not all (155), studies of myocardial ischemia. However, paradoxically, several studies have shown that inhibition of NHE1 renders pH_i unaltered or even less acidic in myocardial ischemia, presumably because the NHE1-dependent Na⁺ and Ca²⁺ accumulation stimulates ATP hydrolysis and thus H⁺ production (8, 155, 232, 261, 286; see also Ref. 264). Moreover, both beneficial and deleterious effects of acidic pH_i during cardiac ischemia/reperfusion have been described. Elevation of pH_i facilitates hypercontracture, and ischemia-induced cardiomyocyte damage and hypercontracture was inhibited both by blocking NHE1 and by inducing extracellular acidification, which, as noted above, can also inhibit NHE1 (26, 145). On the other hand, acidic pH_i facilitates cell death by apoptosis, at least in part, because many apoptotic proteases and DNAses exhibit an acidic pH optimum (see also section 5.2).

Inhibition of NHE1 by 5'(N-ethyl-N-isopropyl)amiloride (EIPA) or cariporide has repeatedly been found to reduce ATP-depletion in cardiac ischemia (155, 232, 253, 261), and NHE1^–/– mice exhibit better cardiac ATP preservation than wild-type mice, both at the end of ischemia and at the end of reperfusion (324). These findings strongly indicate that NHE1 activity contributes to ATP depletion in cardiac ischemia, presumably to a large extent, reflecting the energetic cost of, e.g., increased Na⁺-K⁺-ATPase and Ca²⁺-ATPase activity, resulting from the NHE1-dependent increases in [Na⁺]_i and [Ca²⁺]_i (for a discussion, see, e.g., Ref. 8).

In human neuroblastoma cells (a model for cardiac sympathetic nerve endings), ANG II acting on AT₁ receptors was found to stimulate NHE1 activity, and this led to NE release by NET reversal from reuptake to release mode (244, 280). Thus it appears that excessive carrier-mediated NE release during myocardial ischemia/infarction may, at least in part, reflect reversal of the Na⁺-dependent NET in sympathetic nerve endings because of the NHE1-mediated increase in [Na⁺]_i.

Interestingly, there is evidence that NHE1 can be upstream, rather than downstream, of MAPK activation in the heart also under conditions similar to those occurring in ischemia/reperfusion. Thus ANG II- and 5-HT-mediated ERK1/2 activation in rat aortic smooth muscle cells were mediated via NHE1-dependent Ras-Raf-MEK activation (187). In a rabbit model of nonischemic heart failure, p38 MAPK phosphorylation, as well as apoptosis, fibrosis, myocyte cross-sectional area, and intracellular nitric oxide synthase expression were all significantly reduced by treatment with the NHE1 inhibitor BIIB722 (3). In addition, NHE1 stimulation by cardiomyocyte stretch is upstream of stretch-induced Raf-1 and MAPK activation and subsequent hypertrophy (299, 333; see also above, section 3.1.1).

NHE1 inhibitors also attenuate cardiac myocyte swelling in ischemia (13). Moreover, NO and ·OH release after cardiac ischemia/reperfusion in rat hearts was secondary to increases in NHE1 and NCX activity (164), suggesting that NHE1 stimulation in the heart may also be upstream rather than downstream of the ROS formation known to contribute to ischemia/reperfusion damage (section 4.1.1.2 [EC] ).

Finally, NHE1-mediated cardiac endothelial cell swelling could contribute to ischemic damage, e.g., by reducing capillary diameter, potentially diminishing RBC and leukocyte flow. Consistent with this postulate, in endothelial cells, NHE inhibitors attenuated swelling induced by lactacidosis (18) and by low-flow ischemia (171).

4.1.3 Mechanisms and Consequences of Stimulation of NKCC1 Furosemide and bumetanide inhibit Na⁺ influx and reduce injury during hypothermic ischemia in rat hearts (252), and findings in isolated perfused hearts from both rabbit and rat indicate that NKCC1 is stimulated by ischemia and remains active during reperfusion (7, 13, 252). Moreover, ischemic preconditioning stimulated NKCC1 in hearts of newborn rabbits (9). It is important to note that in marked contrast to the substantial driving force for Na⁺ influx via NHE1, the force driving NKCC1 can actually be directed out of the cell in cardiac ischemia as a consequence of the robust Na⁺ uptake via NHE1. In rabbit hearts perfused with ouabain-containing K⁺-free solution (i.e., outward directed driving force for NKCC1), bumetanide augmented [Ca²⁺]_i elevation during ischemia (1 h) and reperfusion, and inhibited [Na⁺]_i recovery on reperfusion. This indicates that under these conditions, NKCC1 contributes to Na⁺ efflux during reperfusion (7). Under normal [K⁺]_o conditions, data were consistent with the interpretation that in the early phase of ischemia, the driving force for NKCC1 is directed into the cell and NKCC1 contributes to ischemia-induced [Na⁺]_i elevation, whereas later in ischemia the driving force for NKCC1 is directed outward, and NKCC1 functions as a Na⁺ efflux pathway (7). Thus several lines of evidence point to activation of NKCC1 by cardiac hypoxia/ischemia. On the other hand, although direct comparisons of the relative roles of NHE1 and NKCC1 in myocardial ischemia/severe hypoxia are essentially lacking, there is evidence to suggest that at least in rat hearts, the role of NKCC1 may be more modest than that of NHE1 (52, 241).

4.1.3.1 Mechanisms of stimulation of NKCC1. The mechanism(s) of ischemia-induced NKCC1 stimulation in the heart have, to the knowledge of the authors, not been investigated directly. As noted above (section 2.4.2), NKCC1 is generally inhibited by acidic pH_i. This would tend to limit its activity under ischemic conditions, however, to our knowledge, the potential effect of pH_i on NKCC1 activity during cardiac ischemia has not been studied directly.

Several signaling pathways known to be active in the ischemic heart (section 4.1.1.2 [EC] ) stimulate NKCC1 and thus may play a role in ischemic NKCC1 activation. In rat myocardium, NKCC1 was phosphorylated and activated by catecholamines via ₁-AR receptors in an ERK1/2 dependent manner (6). ANG II, aldosterone, and increases in [Ca²⁺]_i have also been proposed to stimulate the myocardial NKCC1 (see Ref. 6), and thrombin is a well-known activator of NKCC1 (215).

4.1.3.2 Consequences of stimulation of NKCC1. In diabetic rat hearts, in which basal NKCC1 activity is increased, NKCC1 was found to contribute to ischemic damage, whereas no contribution of NKCC1 to ischemic damage could be detected in nondiabetic rat hearts (241). Bumetanide inhibited the ischemia-induced increase in [Na⁺]_i in both control and diabetic hearts, but significantly more so in the latter, and only in diabetic hearts was NKCC1 inhibition associated with reduced ATP depletion and improved functional recovery on reperfusion (241). This suggests that, at least in the rat, the role of NKCC1 in cardiac ischemia may be modest; essentially no ouabain-insensitive ⁸⁶Rb⁺ influx was noted in another study of rat hearts exposed to low-flow ischemia (52). Whether this is particular to rats is, to our knowledge, unknown. Recent findings in newborn rabbit hearts suggest that NKCC1, when functionally coupled with Cl^–/HCO₃^– exchange, can be linked to changes in pH_i during ischemia (that is, Cl^– entering on NKCC1 is recycled out of the cell via AE in exchange for HCO₃^– influx to elevate pH_i, or vice versa, if the driving force for NKCC1 is directed out of the cell) (9). Thus after preconditioning, acidification during ischemia was relatively decreased in the presence of bumetanide (9). Similarly, inhibition of NKCC1 was associated with increased pH_i during ischemia in the diabetic rat hearts (241). These results are consistent with the hypothesis that during late ischemia, after [Na⁺]_i and [Cl^–]_i have risen (7), the force driving NKCC1 is directed out of the cell, such that NKCC1 inhibition limits Cl^– and Na⁺ loss via NKCC1 and thereby functionally coupled HCO₃^– loss via AE.

4.2 Ischemia and Severe Hypoxia in the Brain

4.2.1 General Aspects
4.2.1.1 Energy status and ion homeostasis. Similar to cardiac ischemia, cerebral ischemia has been found to be associated with a marked decrease in cellular ATP levels (see Ref. 154). In cultured BBB endothelial cells on the other hand, ATP levels were unaltered through 4 h of hypoxia (the approximate time of edema formation in stroke), even at very low O₂ levels or in the absence of glucose, and after 24 h of hypoxia, ATP levels fell by only 50% (81). Both pH_o and pH_i in the brain of normoglycemic animals can fall by a full pH unit in hypoxia (see Refs. 154 and 338). However, transient elevation of pH_i above steady state has also been described in brain cells exposed to ischemia or simulated ischemia, both in culture and in vivo (124, 279). Intracellular space comprises about 80% of the total space occupied by the brain. In ischemia, major ionic shifts occur between the intra- and extracellular spaces, including, most notably, increased [Na⁺]_i, [Ca²⁺]_i, and [Cl^–]_i, and decreased [K⁺]_i, accompanied by the corresponding inverse changes in these ions in the extracellular space (103, 154, 248). Similar to the situation in the heart, increases in [Na⁺]_i during ischemia favor NCX-mediated Ca²⁺ influx and consequent Ca²⁺-induced cell damage (111), and the rapid increases in [Na⁺]_i and [Ca²⁺]_i together with swelling of neurons, astrocytes, and endothelial cells are major causes of brain damage associated with limited perfusion (33, 90, 124, 135, 142, 177, 278, 288). The extent of [Na⁺]_i elevation and cell swelling varies depending on location in the ischemic region, with the most pronounced effects occurring in the core of the ischemic zone and more moderate slower onset effects in the penumbral regions (130).

Under normal conditions, the BBB mediates Na⁺, Cl^–, and water influx into the brain interstitial fluid and in so doing secretes (i.e., transports from blood into brain) up to 30% of the brain interstitial fluid (the remainder produced by the choroid plexus) (55). During the early hours of cerebral ischemia, brain edema forms by a process involving increased secretion of Na⁺ and water across an intact BBB (135, 178, 262). At the same time, ischemia stimulates NHE1- and/or NKCC1-dependent uptake of Na⁺, Cl^–, and water into astrocytes, causing cytotoxic edema (31, 135, 144), a process likely facilitated by the increased BBB secretion of Na⁺, Cl^–, and water into the brain interstitium (229). In other words, whereas BBB breakdown and consequent paracellular solute and water uptake does not occur until after prolonged ischemia (4–6 h), the Na⁺ and water uptake, which is the basis for brain edema in the early hours of ischemic stroke, occurs before BBB breakdown, indicating that it is transcellular and thus transporter mediated (22). As described below, both NHE1 and NKCC1 appear to play a role in the ionic shifts and cell damage elicited by cerebrovascular ischemia/hypoxia.

4.2.1.2 Signaling events. With the important exception of the elevated glutamate levels found in cerebral ischemia (154), many of the signaling events elicited by ischemia, anoxia, and prolonged hypoxia in the brain are similar to those described above for the heart. ANG II release resulting from activation of the brain renin-angiotensin system appears to be involved in brain damage elicited by ischemic stroke (56), and ET-1 release has also been found to contribute to ischemic cell damage in the brain (see Refs. 133 and 297). There is evidence for the involvement of centrally released arginine vasopressin (AVP) in brain ischemia and consequent cell damage (62, 275). Brain thrombin levels have also been proposed to be elevated after cerebral ischemia and to contribute to ischemic damage (113). Cytokines and inflammatory mediators released, at least in part, from astrocytes and brain microglia also play important roles, and specifically both IL-1 and IL-6 appear to contribute to ischemic brain damage (250, 343). As in the heart, changes in the activity of the MAPKs ERK1/2, JNK, and p38 MAPK (73), as well as of several other protein kinases, have been reported in the ischemic brain (see Ref. 154). Finally, ROS release in the brain is increased during both ischemia and (more so) during reperfusion, and this appears to contribute to ischemia/reperfusion-induced cell damage (see Ref. 154).

4.2.2 Mechanisms and Consequences of Stimulation of NHE1 Ischemic/anoxic/hypoxic NHE1 stimulation and protective effects of NHE1 inhibitors have been described in neurons from many brain regions, including mouse neocortical neurons (124), rat cortical neurons (317), and rat hippocampal CA1 neurons (270, 337), as well as in glial cells (27, 121, 234) and in brain endothelial cells (23, 109, 307). Moreover, protective effects of NHE1 inhibitors have been demonstrated in in vivo models of brain ischemia (317). Similar to what has been found in the heart, however, NHE1 is not the only culprit; NKCC1 (section 4.2.3), tetrodotoxin-sensitive Na⁺ channels (86), and Na⁺ influx via ionotropic glutamate receptors (90) have been found to contribute to the ischemia-induced increase in [Na⁺]_i in the CNS.

4.2.2.1 Mechanisms of stimulation of NHE1. In rat hippocampal CA1 neurons, NHE1 is stimulated by anoxia followed by reoxygenation, yet is apparently inhibited during the anoxia phase per se, possibly because of a reduced cellular ATP level under these conditions (270, 337). Similar to the situation in the heart, pH in the brain decreases very rapidly by up to a full pH unit in response to hypoxia (section 4.2.1.1 [EC] ); thus it appears likely that acidic pH_i contributes to stimulation of NHE1. On the other hand, in mouse astrocytes, in which OGD is associated with intracellular acidification (137), NHE1 activation during in vitro ischemia in mouse astrocytes was proposed to be independent of prolonged acidosis (136). Similarly, in these cells, the rate of pH_i recovery after intracellular acid loading by NH₄ washout was increased by >80% after a 2-h exposure to OGD (137), suggesting that OGD-induced stimulation of NHE1 involves other mechanisms than an acidification-induced increase in activity.

Catecholamines, specifically NE, appear to play an important role in ischemia-induced increases in NHE activity in the brain via ₁- and ₂-ARs and the cAMP/PKA pathway (282); however, at least in CA1 neurons, NE-mediated NHE activity was found to be amiloride insensitive (282). Hence, although NHE1 is also present in CA1 neurons and stimulated during anoxia (99, 337), the -AR-stimulated NHE in these neurons may be NHE5, which is found almost exclusively in the CNS and which has been proposed to be the amiloride-insensitive brain NHE (240).

NHE1 activation during in vitro ischemia in mouse astrocytes has been proposed to be partially dependent on ERK1/2, although the upstream signal leading to ERK1/2 activation was not identified (136). Cytokines released during ischemia and severe hypoxia may also play a role in NHE activation in the brain, as IL-1 and IL-6 have been shown to stimulate NHE1 in astrocytes (21). In contrast to the proposed role of ROS in NHE1 activation during cardiac ischemia/reperfusion, the few available studies indicate that ROS may inhibit NHE activity in the brain (188, 309). Finally, in brain microvascular endothelial cells, NHE1 was reported to be stimulated by ET-1 (315).

4.2.2.2 Consequences of stimulation of NHE1. Elevation of [Ca²⁺]_i is an important cause of the damage induced by ischemia and severe hypoxia in the brain (154, 277, 284). As in the heart, NCX reversal has been found to be involved in ischemia-induced Ca²⁺ influx and consequent damage in both neurons and glial cells (27, 111, 150). The relative contributions of NHE1 and NKCC1 to the disruption of Ca²⁺ homeostasis in the ischemic brain have, to our knowledge, not been directly investigated. However, at least in mouse astrocytes, OGD-induced changes in Ca²⁺ homeostasis were mainly dependent on NKCC1 (150; see also section 4.2.3); hence, it appears that, whereas NHE1 is clearly a major player in disruption of Ca²⁺ homeostasis in the ischemic heart, NKCC1 may, in some cases, be more important in the brain. In glial cells, stimulation of NHE1 by ischemia/hypoxia or lactic acidosis and protective effects of NHE1 inhibition against glial cell swelling and death, under these conditions, have been demonstrated in a variety of preparations (27, 121, 234). Consistent with the view that NHE1 contributes importantly to the hypoxia-induced increase in Na⁺ transport across the BBB, NHE1 inhibition is protective against hypoxia-induced brain endothelial cell dysfunction and BBB disruption (23, 109, 307), and intravenous HOE-642 and bumetanide to inhibit BBB NHE1 and NKCC1 activity was recently found to decrease edema formation and cerebral infarct size in middle cerebral artery occlusion (MCAO) in the rat, apparently in an additive manner (307 and O'Donnell ME, unpublished observation).

Stimulation of NHE1 during ischemia and severe hypoxia in the brain appears to ameliorate the decrease in pH_i during both ischemia and reperfusion. In mouse neocortical neurons in primary culture, NHE1 inhibition exacerbated acidification during chemical anoxia and inhibited pH_i recovery on "reperfusion" (124). Similar to the findings in the heart, a "pH paradox" of both protective and damaging effects of acidic pH has been described in the brain. Mild acidosis is protective in brain ischemia, at least partly, by attenuating Ca²⁺ influx via N-methyl-D-aspartate (NMDA) and -amino-3 hydroxy-5-methylisoxazole-4 propionic acid (AMPA) receptors and voltage-dependent Ca²⁺-channels and by reducing energy demand and ATP depletion (102, 305), but likely also because of the inhibition of NHE1 by acid pH_o (317). Acid pH_o, which inhibits NHE1 activity, was neuroprotective in chemical anoxia in dissociated cortical cultures, apparently, at least in part, because of NHE1 inhibition (317). Consistent with the notion that NHE1 exhibits little activity during the ischemic phase per se, this effect of acidic pH_o was only seen during reperfusion (317). Similarly, in mouse neocortical neurons, in which an EIPA-sensitive NHE is a major regulator of pH_i after acidification, EIPA and acidic pH_o both reduced pH_i recovery (223), and acidic pH_o (EIPA not tested) attenuated the increase in [Ca²⁺]_i during chemical anoxia (124). Ischemia/reperfusion-induced free fatty acid release is shown to be reduced by inhibition of NHE1, perhaps because of a pH effect on phospholipase A₂ (233). If, however, pH_i is too acidic, this will favor cell death by apoptosis (section 5.2). Acidic pH_i has also been demonstrated to potentiate ROS formation in the brain directly, to inhibit mitochondrial metabolism (thus accelerating ATP depletion), and to exacerbate neuronal death (338).

4.2.3 Mechanisms and Consequences of Stimulation of NKCC1 NKCC1 knockout mice exhibit reduced brain damage in stroke models (47), and, as described below, there is evidence for roles for NKCC1 in ischemic damage in neurons, astrocytes, and brain endothelial cells. Early studies provided evidence that a luminal Na⁺ transporter, working in tandem with abluminal Na⁺/K⁺ pump and Cl^– efflux pathways, is rate limiting in BBB Na⁺ secretion (24, 262). More recent data strongly indicate that NKCC1 serves as such a luminal Na⁺ uptake pathway during ischemia. Thus NKCC1 resides predominantly in the luminal membrane of BBB endothelial cells in situ (205) and is stimulated by AVP (203), hypoxia (81), and aglycemia (81), prominent factors present during cerebral ischemia.

4.2.3.1 Mechanisms of stimulation of NKCC1. In the brain, mechanisms of NKCC1 activation in ischemia are better understood than in the heart, although far from fully elucidated. Elevated extracellular K⁺ and glutamate levels (154), both of which occur in cerebral ischemia (section 4.2.1) have been found to stimulate NKCC1 activity in neurons (Fig. 3A). Thus activation of both ionotropic and metabotropic NMDA receptors, as well as of AMPA receptors, activated NKCC1 in cortical neurons, as did high [K⁺]_o-induced depolarization, both in a Ca²⁺-dependent manner (17, 266). Elevated [K⁺]_o also increased NKCC1 activity in glial cells, similarly in a Ca²⁺-dependent manner (290; Fig. 3B).

View larger version (24K): [in this window] [in a new window]   Fig. 3. Major mechanisms and consequences of ischemia/hypoxia-induced activation of NKCC1 in neurons, glial cells, and brain endothelial cells. A: neurons. B: glial cells. C: brain microvascular endothelial cells (blood-brain barrier). depol., Depolarization; EAA, excitatory amino acid; ET-1, endothelin-1; VSOR, volume-expansion sensing outward rectifying anion channel; AVP, arginine vasopressin; P, phosphorylation.

Cytokines, long known as mediators of ischemic brain damage (section 4.2.1.2 [EC] ) may be involved in ischemia-induced increases in NKCC1 activity. Thus IL-6 released by astrocytes was shown to activate NKCC1 in brain endothelial cells (293), and the immunosuppressant FK506, which prevents IL-6 upregulation in astrocytes and microglia, reduced infarct volume in a rat MCAO model (343).

Similar to other mechanisms of acute stimulation of NKCC1, ischemia-induced increases in NKCC1 activity are generally associated with increased NKCC1 phosphorylation on ser¹⁸⁴ and ser¹⁸⁹, as reported in rat cerebral cortex at 4–8 h of reperfusion after MCAO (334) and in mouse cortical astrocytes after 2 h of OGD (150). Similarly, both hypoxia and AVP increased the phosphorylation of NKCC1 in cultured bovine cerebral microvascular endothelial cells (81). The protein kinases that mediate ischemia-induced NKCC1 phosphorylation in the brain are unknown; however, several candidates are known to be activated in the ischemic brain (section 4.2.1.2 [EC] ). Not only posttranslational regulation appears to be important, e.g., in rat model of focal cerebral ischemia/reperfusion (2-h MCAO and 24-h reperfusion), NKCC1 protein levels were significantly upregulated in the cortical neurons at the end of reperfusion (336), and similar findings were reported in whole rat cerebral cortex and striatum (334).

Interestingly, at least in BBB endothelial cells, a decrease in cellular ATP is not necessary for hypoxia-induced stimulation of NKCC1 (81). In these cells, hypoxia is a rapid and potent stimulator of NKCC1, counter to the common assumption that BBB cells are highly resistant to hypoxia (81). Simply removing glucose and pyruvate increases NKCC1 activity in the BBB cells under normoxic conditions (81; Fig. 3C). In the presence of pyruvate, glucose has no effect on the ability of hypoxia to stimulate NKCC1; however, if pyruvate is removed, NKCC1 activity is increased 2.6-fold both in normoxia and in hypoxia (81). Thus NKCC1 activity in BBB endothelial cells appears to be very sensitive to changes in metabolic profile, rather than just to a decrease in PO₂ (81).

Finally, it may be noted that recent findings from O'Donnell, et al. (204) indicate that a reduction in NKCC1 activity in astrocytes and BBB endothelial cells, and consequent reduced edema formation, contributes to the neuroprotective effects of estradiol in stroke.

4.2.3.2 Consequences of stimulation of NKCC1. Studies of NKCC1 knockout mice (47), as well as studies employing intracerebral bumetanide administration, strongly indicate an important role of NKCC1 in ischemic brain damage. Bumetanide potently reduced neuron and astrocyte swelling and infarct volume after focal cerebral ischemia in rats (2-h MCAO followed by 24-h reperfusion) (336). Several studies have specifically addressed the involvement of NKCC1 in neuronal damage (Fig. 3A). NKCC1 inhibition was found to inhibit the increase in [Na⁺]_i, cell swelling, and cell death elicited by OGD or glutamate in 14- to 15-day cortical neurons in vitro (17). In rat hippocampus, furosemide and bumetanide enhanced ATP recovery after OGD and attenuated CA1 neuronal injury (236). In astrocytes, NKCC1 is an important contributor to the cell swelling and excitatory amino acid (EAA) release in response to high [K⁺]_o (a condition prevalent in the ischemic brain, see section 4.2.1.1 [EC] ). In accordance with this, astrocytes from NKCC1^–/– mice exhibit absence of swelling and decreased EAA release after high [K⁺]_o (289, 290). The main mechanism in NKCC1-mediated EAA release appears to be that NKCC1-induced cell swelling activates the volume-expansion sensing outward rectifying anion channel (also known as the volume-regulated anion channel), through which EAA are released (255; Fig. 3B). In postnatal day 10 (P10), rat optic nerve astrocytes, OGD-induced cell swelling, and necrotic cell death were dependent on NKCC1 (302). In mouse cortical astrocytes, Na⁺ uptake by NKCC1 appeared to contribute to NCX-mediated Ca²⁺-loading of intracellular Ca²⁺ stores during ischemia (Fig. 3B). Thus 2 h of OGD followed by 1 h of reperfusion elicited [Na⁺]_i elevation and cell swelling, both of which were attenuated by bumetanide and by genetic ablation of NKCC1 (150). OGD, moreover, elicited an increase in agonist-induced Ca²⁺ release, which was inhibited by bumetanide, absent in astrocytes from NKCC1^–/– mice, and inhibited by KB-R7943, an inhibitor of Ca²⁺ entry via NCX (150).

Increased NKCC1 activity in BBB endothelial cells also appears to contribute importantly to the detrimental effects of brain ischemia (Fig. 3C). In rat brain, NKCC1 was found predominantly on the luminal side of the microvascular endothelial cells, and administration of intravenous bumetanide to inhibit the BBB cotransporter significantly attenuates edema formation in the rat MCAO model of stroke, whether added 20 min before or after onset of MCAO (205, 306, 307). These findings underscore the important role for NKCC1 in mediating solute uptake across the BBB and suggest that ischemia-induced increases in NKCC1 activity elicits excessive solute uptake, resulting in brain edema. In contrast to findings in rat brains, where microdialysis of bumetanide into the cortices was only protective if administered preischemia (334), bumetanide has also been shown to reduce edema and infarct size in rat brain, even when administered after MCAO (306), i.e., the remaining 20% perfusion during MCAO is sufficient to deliver bumetanide to the BBB NKCC1. This is of obvious clinical interest, as it indicates that bumetanide given after the onset of stroke may still be beneficial in reducing edema and infarct size.

As noted above (section 3.2.2), [Cl^–]_i is a major determinant of GABAergic signaling (increased [Cl^–]_i being associated with attenuation or even reversal of the inhibitory effect of GABA, and thus increased excitability). It is thus likely that the detrimental effect of increased NKCC1 activity in the ischemic brain may, at least in part, reflect elevation of [Cl^–]_i; however, this has, to our knowledge, not been directly investigated.

Finally, another consequence of increased NKCC1 activity may be modulation of the activity of stress-activated protein kinases. NKCC1 associates directly with SPAK and the related kinase oxidative stress response 1 (230, 231), members of the germinal center kinase subfamily of the ste 20-related kinases, both of which are expressed in the brain (230). In brain slices, NKCC1, SPAK, and p38 MAPK were found to form a complex from which p38 MAPK appeared to dissociate on ischemic stress, leading to the proposal that NKCC1 may play a scaffolding role in regulating the cellular stress response (230).²

4.3 Ischemia and Severe Hypoxia in the Blood

4.3.1 General Aspects In their capacity as O₂-CO₂ transporters, RBCs play a central role in the responses to hypoxic stress. Although this review only deals with the possible role of RBCs, it should also be noted that both platelets (180) and leukocytes contribute importantly to the response to ischemia/hypoxia (see Refs. 139 and 154).

4.3.1.1 Energy status and ion homeostasis. In mouse RBCs, cellular ATP levels were unaffected by 1 h of hypoxia (0.5% O₂) (25). In RBCs with mitochondria (e.g., nucleated RBCs from birds or teleosts or mammalian reticulocytes), low oxygen conditions can elicit a shift from oxidative to glycolytic metabolism and are associated with decreased ATP levels (although this may, in fact, not be caused by decreased oxidative metabolism, see e.g., Ref. 198). Even in nonnucleated RBCs, glycolysis is increased by deoxygenation (179; see Ref. 89).

In contrast to the pH_i decrease induced by deoxygenation in the heart and brain (see sections 4.1.1.1 [EC] and 4.2.1.1 [EC] ), deoxygenation per se will lead to an increased pH_i of RBCs because of the Haldane effect (the effect of oxygenation on the H⁺-binding properties of Hb) (197). Deoxygenation, moreover, increases free cytoplasmic Mg²⁺ concentration purely as a result of the Hb oxy-deoxy changes (79, 239). Finally, some cell swelling will occur in hypoxic RBCs solely because of the Cl^– shift induced by deoxygenation (75). If NKCC1 and/or NHE1 is stimulated under conditions in which the driving force favors Na⁺ influx via these transporters, deoxygenation is expected to increase [Na⁺]_i and [Cl^–]_i, and in some cases also [K⁺]_i, and elicit further cell swelling. Precisely such effects were reported in RBCs from several species, including trout and turkey (75, 192). On the other hand, [Na⁺]_i and [K⁺]_i in mouse RBCs were reported to be essentially unaffected by 45 min of hypoxia, as well as by 15-min hypoxia followed by 15-min reoxygenation (25). With respect to [Ca²⁺]_i, this was reported to be elevated in RBCs for several weeks after myocardial ischemia in human patients (118). Oxidative stress or energy depletion of mammalian RBCs also appears to be associated with increased [Ca²⁺]_i (148). On the other hand, experimental deoxygenation of human RBCs had no detectable effect on [Ca²⁺]_i (303).

4.3.1.2 Signaling events. RBCs are obviously exposed to the many extracellular mediators released to the bloodstream during ischemia and severe hypoxia, including, e.g., catecholamines (adrenaline, noradrenaline), ET-1, AVP, dopamine, and atrial natriuretic peptide (ANP), as measured in human patients following cerebral infarction or stroke (16, 70, 193). The extent to which the RBCs have functional receptors for these mediators is likely to differ with species and RBC age/developmental stage. For instance, it has been reported that mature human RBCs lack functional receptor-coupled adenylate cyclase systems (72), although, in apparent contrast to this, NHE1 in human RBCs was reported to be stimulated by catecholamines, in part, via ₁-receptors (30).

Numerous studies point to important roles of protein kinases in the oxygen-dependent regulation of NHE1 and NKCC1 in RBCs (section 3.3); however, the molecular identity of these putative hypoxia-activated kinase(s) is essentially unknown. Changes in redox systems may also be important signaling events in deoxygenated RBCs. In RBCs, ROS are formed to a degree proportional to PO₂, because of the high levels of ferrous iron and reducing enzymes (50). Therefore, hypoxia should decrease ROS production and prevent oxidation of reduced glutathione (GSH). Consistent with this, an increase in GSH levels was noted in mouse RBCs exposed to hypoxia (25).

4.3.2 Mechanisms and Consequences of Stimulation of NHE1 As pointed out above (section 3.3.1), it is well established that NHE1 is activated by hypoxic conditions in RBCs from lower vertebrates (89). It seems highly probable that this is the case also in mammalian RBCs, since multiple factors known to stimulate NHE1 are released to the bloodstream during ischemia in mammals (section 4.3.1.2 [EC] ). However, studies directly addressing the effect of hypoxia on NHE1 in mammalian RBCs appear to be lacking. In mammals, ischemia-induced NHE1 activation may only be of real consequence in RBCs, such as those of rabbits and dogs, or in reticulocytes, which exhibit robust transporter activities, since NHE1 activity in mature human RBCs is relatively minor (41, 123, 216; see also Ref. 222).

4.3.2.1 Mechanisms of stimulation of NHE1. In the RBCs of lower vertebrates, NHE1 is activated by deoxygenation per se, by a mechanism that has yet to be fully understood but may involve changes in redox systems, membrane-bound Hb, and protein kinase activity (section 3.2.3, and for an in-depth discussion, see Ref. 89).

In addition to this, hypoxic stimulation of NHE1 in the RBCs of most teleosts is also dependent on circulating catecholamines (see section 3.3.1). In flounder RBCs, catecholaminergic stimulation of NHE1 was, at least in part, PKA-dependent, and was mediated by a pathway distinct from that involved in stimulation of NHE1 by osmotic cell shrinkage or by inhibition of PP1 and PP2A (108). The elevated plasma level of catecholamines that results from ischemic stress in mammals (section 4.3.1.2 [EC] ) has also been reported to increase NHE1 activity in human RBCs, possibly, via both ₁- and ₂-ARs (30), although this may be of minor consequence given the low NHE1 activity in these cells. Similarly, ANP, the plasma level of which is increased in ischemia (section 4.3.1.2 [EC] ) has been reported to stimulate NHE1 in human RBCs, an effect proposed to be mediated via cGMP (228).

In contrast to the prominent role of intracellular acidification in ischemic/hypoxic NHE1 stimulation in the heart and brain, acid pH_i is unlikely to be a major pathway for NHE1 stimulation in ischemic/hypoxic RBCs. Although plasma pH_i can be decreased in extreme hypoxia (75), deoxygenation per se will tend to increase pH_i in RBCs because of the Haldane effect (section 4.3.1.1 [EC] ). Moreover, Hbs of mammalian RBCs exhibit very high H⁺-buffering capacities; thus the effect of anoxia on pH_i is likely to be limited (40). ROS may also be unlikely to mediate hypoxic/ischemic stimulation of NHE1 in RBCs, since H₂O₂ was found to inhibit NHE1 in trout RBCs (199).

4.3.2.2 Consequences of stimulation of NHE1. In teleosts, hypoxic NHE1 activation in RBCs will elicit an elevation of pH_i and cell swelling, both of which will increase the O₂ affinity and saturation of Hb by virtue of the Bohr and Root effects (197). In humans, these effects could, in principle, apply but are likely to be modest because of the limited net NHE1 activity in mature human RBCs and the different Hb properties in mammals compared with teleosts (see above, and for a discussion, see Ref. 222). Reduced RBC deformability reduces blood flow (217), an effect that has been proposed to contribute to ischemic damage (304). The RBC swelling resulting from hypoxic activation of NHE1 could therefore in principle elicit detrimental effects on blood rheological properties, although this has yet, to our knowledge, to be directly investigated. It may also be noted that RBC lysis, which could be caused or facilitated by severe RBC swelling, contributes to ischemic damage, e.g., as shown in rat brain (113).

4.3.3 Mechanisms and Consequences of Stimulation of NKCC1 In RBCs from birds, ferrets, and humans, NKCC1 is stimulated by deoxygenation per se (64, 79, 192; see Ref. 89). On the other hand, in mouse RBCs, NKCC1 was reported to be unaffected by hypoxia (25), pointing to the existence of species-specific effects of hypoxia on NKCC1 activity.

Similar to that of NHE1, NKCC1 activity is modest in mature mammalian RBCs compared with the activity in reticulocytes or in nucleated RBCs (64, 166). On the other hand, at least under conditions of robust driving forces and high hematocrit, NKCC1 activity is high enough even in mammalian RBCs to elicit significant physiological effects (see Ref. 89), although little direct evidence is available for ischemia and severe hypoxia, as discussed below (section 4.3.3.3 [EC] ).

4.3.3.1 Mechanisms of stimulation of NKCC1. NKCC1 in RBCs is expected to be stimulated by the elevated plasma levels of catecholamines and other NKCC1-activating factors resulting from ischemic insults (section 4.1.3.2 [EC] ), as well as by the above-described stimulation by deoxygenation per se. The mechanism(s) of stimulation of NKCC1 by a reduction in PO₂ per se are not fully elucidated. A role for Mg²⁺ seems possible, since increased [Mg²⁺]_i stimulates NKCC1 (see Ref. 254) and deoxygenation, as noted above, increases [Mg²⁺]_i (239). However, neither the increase in [Mg²⁺]_i (79) nor the increase in pH_i expected purely on the basis of Hb conformational changes on deoxygenation of RBCs (section 4.3.1.1 [EC] ), are likely to be sufficient to explain the marked stimulation of NKCC1 by deoxygenation. Studies in both avian and mammalian RBCs have strongly indicated a central role for a putative deoxygenation-activated protein kinase(s). In avian RBCs, increased NKCC1 phosphorylation was proposed to occur upon RBC deoxygenation (192). In ferret RBCs, thr phosphorylation of NKCC1 did not appear to be increased upon deoxygenation-induced stimulation, suggesting a pathway different from that mediating NKCC1 stimulation, by e.g., protein phosphatase inhibitors (79).

4.3.3.2 Consequences of stimulation of NKCC1. As described in section 3.3.3, hypoxia-induced NKCC1 activation in RBCs will, under conditions of an inwardly directed driving force for this transporter, tend to elevate K⁺ and may serve to buffer increases in plasma [K⁺]. Similarly, RBC swelling resulting from increased NKCC1 activity will increase the O₂ affinity and saturation of Hb but could also cause rheological problems, as noted above for NHE1 (section 4.3.2.2 [EC] ). Also, as discussed above, the gradient for NKCC1 is not always inwardly directed in RBCs (see sections 3.3.2 and 4.1.3.2 and also Ref. 166), such that in ischemia and severe hypoxia, where shifts in intra- and extracellular [Na⁺] and [K⁺] occur, the direction of transport via NKCC1 is hard to predict. Under conditions eliciting substantial outward flux via NKCC1, this could, in principle, contribute to apoptotic RBC shrinkage and ultimately death (section 5); however, to our knowledge, the relevance of this phenomenon to ischemia and severe hypoxia has not been directly studied.

	5 NHE1- and NKCC1-Mediated Cell Death in Ischemia and Severe Hypoxia

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5.1 Cell death in ischemia and severe hypoxia—apoptosis or necrosis?

Apoptosis and necrosis are classically described as two distinct forms of cell death with fundamentally different characteristics. Cell death by apoptosis involves membrane blebbing, outer membrane leaflet inversion, nuclear condensation, and cell shrinkage (74). In contrast, necrosis is characterized by cell swelling and loss of plasma membrane integrity, resulting in the release of cell content to the surrounding milieu (74). As described above, cell swelling is a characteristic feature of ischemia/reperfusion damage in both the heart and the brain (see Refs. 120, 327, and 345), and swelling of RBCs on deoxygenation stress has also been reported (75). In part, for this reason, cell death as a consequence of ischemia was initially thought to be largely necrosis; however, accumulating evidence indicates that both apoptosis (or apoptosis-like, caspase-independent cell death) and necrosis contribute to ischemic cell death in both the heart (211, 345) and brain (93, 196). Whether cells exposed to ischemia or severe hypoxia die by apoptosis or necrosis, by a combination of both, or by some pathway unique to this condition, is a point of some controversy, and is probably dependent on multiple factors, such as cell type and severity of the ischemic insult (see, e.g., Refs. 120 and 196). For instance, apoptosis is an ATP-dependent process, and if ATP levels fall below a critical level, certain stimuli normally leading to apoptotic cell death will instead cause death by a necrotic pathway (see Ref. 74). The increase in [Ca²⁺]_i resulting from ischemia and severe hypoxia will activate death effectors, including Ca²⁺-dependent proteases and initiate mitochondrial apoptotic death pathways. Similarly, ROS are important mediators of apoptosis, in part, because of mitochondrial damage (157). Studies in cardiomyocytes indicate that the combination of hypoxia and low pH_i prevalent in the ischemic heart synergistically trigger a unique death pathway involving the Bcl-2 family death-promoting protein BNIP3 (94). Mammalian RBCs, which lack nuclei and mitochondria, do not undergo classical caspase-dependent apoptosis, yet die following energy depletion or oxidative stress by a caspase-independent form of cell death exhibiting many characteristics of apoptosis, and due, at least in part, to Ca²⁺ influx and increased [Ca²⁺]_i (148).

5.2 Roles of NHE1.

Consistent with a role for NHE1 in ischemia-induced cell swelling in both the heart and the brain, amiloride inhibited cold ischemia-induced cell swelling in rat hearts (13), and genetic ablation of NHE1 inhibited OGD-induced astrocyte swelling (137). NHE1 inhibitors have also been shown to attenuate apoptosis in a number of models of myocardial hypoxia/ischemia and heart failure (3, 15, 44, 294). In one study, cariporide was reported to inhibit ischemia/reperfusion-induced cardiomyocyte death by necrosis, as well as apoptosis (211). The NHE1-mediated necrosis is presumably because of Na⁺ influx and concomitant cell swelling (Fig. 2). Only a few studies have addressed the mechanisms by which increased NHE1 activity leads to apoptotic cell death in ischemia. In neonatal rat cardiomyocytes, the NHE1-mediated increase in [Ca²⁺]_i was proposed to lead to mitochondrial Ca²⁺ overload and activation of a mitochondrial death pathway (294, 300). NHE1-mediated mitochondrial Ca²⁺ overload after in vitro ischemia was also recently reported in mouse astrocytes (136). In cerebellar granule neurons, inhibition of NHE1 alone was found to elicit caspase-independent cell death with morphological features most characteristic of apoptosis (paraptosis) (263). The role of NHE1 in apoptosis is thus not straightforward, and, additionally, antiapoptotic effects of NHE1 have been described in numerous studies of nonischemia conditions (246, 301, 328). An important protective effect of NHE1 in such cases appears to be maintaining pH_i above the acidic pH_i optimum for many death effectors, including caspases and cathepsins (169, 251, 263). Although this is in apparent contrast to the consistently protective effect of NHE1 inhibition in ischemia, it should be kept in mind that inhibition of NHE1 in ischemia may, in fact, somewhat counterintuitively lead to increased pH_i (section 4.1.2.2 [EC] ).

5.3 Roles of NKCC1.

Very few studies to date have addressed the potential involvement of NKCC1 in apoptotic vs. necrotic death following ischemic/hypoxic insults. An important consequence of NKCC1 stimulation by ischemia and severe hypoxia in the brain is neuronal and glial swelling and edema (section 4.2.3.2 [EC] ), pointing to a possible role of NKCC1 in ischemia/hypoxia-induced brain cell necrosis (Fig. 3). To our knowledge, only one study has specifically addressed this issue. The findings indicated that NKCC1 inhibition reduced necrosis, but not apoptosis, after focal ischemia in rat cerebral cortex (334). A few nonischemia studies in tissues other than heart, brain, or blood have implicated NKCC1 in apoptotic cell death (134, 168). In RBCs, outward transport via NKCC1 and concomitant isotonic cell shrinkage has been tentatively proposed to play a role in the apoptotic process (158). As noted above, the driving force for NKCC1 may reverse during ischemia also in the heart (section 4.1.3.2 [EC] ), in principle, allowing similar cell shrinkage. In light of the small extracellular space of the brain, [K⁺]_o is probably sufficiently high in ischemia so that outward transport by NKCC1 seems unlikely. In brain cells, ischemic activation of NKCC1 could, in principle, also lead to an apoptosis-like cell death, for instance, via the above-described entry of Ca²⁺ via NCX and concomitant changes in Ca²⁺ homeostasis (section 4.2.3.2 [EC] , see also Fig. 3); however, this possibility remains to be studied.

	6 Perspectives and Open Questions

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In this review, we have sought to document the considerable progress made in recent years in understanding the physiological and pathophysiological roles of NHE1 and NKCC1 in the heart, the brain, and the blood. Although these transporters are of pivotal importance in the return to tissue homeostasis following various forms of physiological stress, their excessive activity may, under certain pathophysiological conditions, be a major cause of cell damage and death. The overall aim of this review was to evaluate and compare the roles of NHE1 and NKCC1 in the detrimental events resulting from ischemia and severe hypoxia. Specifically, we addressed the similar roles of these transporters in [Na⁺]_i overload leading to NCX reversal, increased [Ca²⁺]_i, and consequent cell death via Ca²⁺-dependent mechanisms, including mitochondrial death pathways. As discussed above, this scheme contributes importantly to the detrimental roles of both of these transporters in ischemia and severe hypoxia in the heart and brain, and there is also evidence to suggest a role in the blood. However, in all of the three tissues, there is increasing evidence for a major involvement of a number of other mechanisms in NHE1- and NKCC1-mediated damage, including changes in pH_i and cell volume, activation of MAPKs, and release of EAAs and ROS. Moreover, it appears that a complex interplay of multiple ischemia/hypoxia-activated signaling events mediates the activation of NHE1 and NKCC1 under these conditions, although the activation pathways are still incompletely described. The mechanisms leading to NHE1 and NKCC1 activation and the mechanisms by which activation of these transporters lead to cell damage and death in ischemia and severe hypoxia constitute potentially interesting targets for therapeutic intervention and should be a focus for future research in this clinically very important field.

	GRANTS

TOP ABSTRACT 2 NHE1 and NKCC1:... 3 NHE1 and NKCC1... 4 NHE1 and NKCC1... 5 NHE1- and NKCC1-Mediated... 6 Perspectives and Open... GRANTS REFERENCES

 
Work in our laboratories cited above was supported by the National Institutes of Health Grants HL-21179 (to P. M. Cala), HL-56681 (to S. E. Anderson), and NS039953 (to M. E. O'Donnell); an American Heart Association Grant-in-Aid (to M. E. O'Donnell); External Research Program Grants from Philip Morris (to M. E. O'Donnell and S. E. Anderson); the Carlsberg Foundation Grant 0544/20 (to S. F. Pedersen); and the Danish Natural Science Research Council Grant 22–01-0055 (to S. F. Pedersen). The nuclear magnetic resonance spectrometer expense was funded, in part, by National Institutes of Health Grant RR02511 and National Science Foundation Grant PCM-8417289.

	ACKNOWLEDGMENTS

 
We apologize to those whose work, although relevant to this review, could not be cited because of space restrictions. The members of our labs are gratefully acknowledged for contributing unpublished data and stimulating discussions.

	FOOTNOTES

 

Address for reprint requests and other correspondence: S. F. Pedersen, Dept. of Biochemistry, August Krogh Bldg., Institute of Molecular Biology and Physiology, Univ. of Copenhagen, 13 Universitetsparken, Dk-2100 Copenhagen Ø, Denmark (e-mail: sfpedersen{at}aki.ku.dk)

¹ The teleost RBC NHE is denoted NHE for its -adrenergic activation, yet it is much more homologous to NHE1 than to any other NHE isoform (in some cases, the homology between a given NHE and an NHE1 is higher than between NHE1 orthologs from different species). Hence, NHE will be grouped as an NHE1.

² It may be noted that SPAK is a regulator of NKCC1 (63, 87), and its role in ischemia-induced NKCC1 activation is yet unclear.

	REFERENCES

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1. Adragna NC, Chang JL, Morey MC, and Williams RS. Effect of exercise on cation transport in human red cells. Hypertension 7: 132–139, 1985.[Abstract/Free Full Text]
2. Aitken PG, Borgdorff AJ, Juta AJ, Kiehart DP, Somjen GG, and Wadman WJ. Volume changes induced by osmotic stress in freshly isolated rat hippocampal neurons. Pflügers Arch 436: 991–998, 1998.[CrossRef][Web of Science][Medline]
3. Aker S, Snabaitis AK, Konietzka I, Van De SA, Bongler K, Avkiran M, Heusch G, and Schulz R. Inhibition of the Na⁺/H⁺ exchanger attenuates the deterioration of ventricular function during pacing-induced heart failure in rabbits. Cardiovasc Res 63: 273–282, 2004.[Abstract/Free Full Text]
4. Allen DG and Xiao XH. Role of the cardiac Na⁺/H⁺ exchanger during ischemia and reperfusion. Cardiovasc Res 57: 934–941, 2003.[Abstract/Free Full Text]
5. Alvarez-Leefmans FJ, Gamino SM, Giraldez F, and Nogueron I. Intracellular chloride regulation in amphibian dorsal root ganglion neurones studied with ion-selective microelectrodes. J Physiol 406: 225–246, 1988.[Abstract/Free Full Text]
6. Andersen GO, Skomedal T, Enger M, Fidjeland A, Brattelid T, Levy FO, and Osnes JB. ₁-AR-mediated activation of NKCC in rat cardiomyocytes involves ERK-dependent phosphorylation of the cotransporter. Am J Physiol Heart Circ Physiol 286: H1354–H1360, 2004.[Abstract/Free Full Text]
7. Anderson SE, Dickinson CZ, Liu H, and Cala PM. Effects of Na-K-2Cl cotransport inhibition on myocardial Na and Ca during ischemia and reperfusion. Am J Physiol Cell Physiol 270: C608–C618, 1996.[Abstract/Free Full Text]
8. Anderson SE, Kirkland DM, Beyschau A, and Cala PM. Acute effects of 17-estradiol on myocardial pH, Na⁺, and Ca²⁺ and ischemia/reperfusion injury. Am J Physiol Cell Physiol 288: C57–C64, 2005.[Abstract/Free Full Text]
9. Anderson SE, Liu H, and Cala PM. Bumetanide limits changes in myocardial Na-i and pH_i during ischemia after preconditioning (Abstract). FASEB J 10: 1848, 1996.
10. Anderson SE, Murphy E, Steenbergen C, London RE, and Cala PM. Na-H exchange in myocardium: effects of hypoxia and acidification on Na and Ca. Am J Physiol Cell Physiol 259: C940–C948, 1990.[Abstract/Free Full Text]
11. Andrew RD, Lobinowich ME, and Osehobo EP. Evidence against volume regulation by cortical brain cells during acute osmotic stress. Exp Neurol 143: 300–312, 1997.[CrossRef][Web of Science][Medline]
12. Armstrong SC. Protein kinase activation and myocardial ischemia/reperfusion injury. Cardiovasc Res 61: 427–436, 2004.[Abstract/Free Full Text]
13. Askenasy N, Vivi A, Tassini M, and Navon G. The relation between cellular sodium, pH and volumes and the activity of Na/H antiport during hypothermic ischemia: multinuclear NMR studies of rat hearts. J Mol Cell Cardiol 28: 589–601, 1996.[CrossRef][Web of Science][Medline]
14. Avkiran M and Haworth RS. Regulatory effects of G protein-coupled receptors on cardiac sarcolemmal Na⁺/H⁺ exchanger activity: signalling and significance. Cardiovasc Res 57: 942–952, 2003.[Abstract/Free Full Text]
15. Baartscheer A, Schumacher CA, van Borren MM, Belterman CN, Coronel R, and Fiolet JW. Increased Na⁺/H⁺ exchange activity is the cause of increased [Na+]i and underlies disturbed calcium handling in the rabbit pressure and volume overload heart failure model. Cardiovasc Res 57: 1015–1024, 2003.[Abstract/Free Full Text]
16. Barreca T, Gandolfo C, Corsini G, Del Sette M, Cataldi A, Rolandi E, and Franceschini R. Evaluation of the secretory pattern of plasma arginine vasopressin in stroke patients. Cerebrovasc Dis 11: 113–118, 2001.[CrossRef][Web of Science][Medline]
17. Beck J, Lenart B, Kintner DB, and Sun D. Na-K-Cl cotransporter contributes to glutamate-mediated excitotoxicity. J Neurosci 23: 5061–5068, 2003.[Abstract/Free Full Text]
18. Behmanesh S and Kempski O. Mechanisms of endothelial cell swelling from lactacidosis studied in vitro. Am J Physiol Heart Circ Physiol 279: H1512–H1517, 2000.[Abstract/Free Full Text]
19. Behnke BJ, Kindig CA, Musch TI, Koga S, and Poole DC. Dynamics of microvascular oxygen pressure across the rest-exercise transition in rat skeletal muscle. Respir Physiol 126: 53–63, 2001.[CrossRef][Web of Science][Medline]
20. Bell SM, Schreiner CM, Schultheis PJ, Miller ML, Evans RL, Vorhees CV, Shull GE, and Scott WJ. Targeted disruption of the murine Nhe1 locus induces ataxia, growth retardation, and seizures. Am J Physiol Cell Physiol 276: C788–C795, 1999.[Abstract/Free Full Text]
21. Benos DJ, McPherson S, Hahn BH, Chaikin MA, and Benveniste EN. Cytokines and HIV envelope glycoprotein gp120 stimulate Na⁺/H⁺ exchange in astrocytes. J Biol Chem 269: 13811–13816, 1994.[Abstract/Free Full Text]
22. Betz AL. Alterations in cerebral endothelial cell function in ischemia. Adv Neurol 71: 301–311, 1996.[Web of Science][Medline]
23. Betz AL, Ennis SR, Ren X, Schielke GP, and Keep RF. Blood-Brain Barrier Sodium Transport and Brain Edema Formation. New York: Plenum Press 1995.
24. Betz AL, Keep RF, Beer ME, and Ren XD. Blood-brain barrier permeability and brain concentration of sodium, potassium, and chloride during focal ischemia. J Cereb Blood Flow Metab 14: 29–37, 1994.[Web of Science][Medline]
25. Bogdanova AY, Ogunshola OO, Bauer C, and Gassmann M. Pivotal role of reduced glutathione in oxygen-induced regulation of the Na⁺/K⁺ pump in mouse erythrocyte membranes. J Membr Biol 195: 33–42, 2003.[CrossRef][Web of Science][Medline]
26. Bond JM, Chacon E, Herman B, and Lemasters JJ. Intracellular pH and Ca²⁺ homeostasis in the pH paradox of reperfusion injury to neonatal rat cardiac myocytes. Am J Physiol Cell Physiol 265: C129–C137, 1993.[Abstract/Free Full Text]
27. Bondarenko A, Svichar N, and Chesler M. Role of Na⁺-H⁺ and Na⁺-Ca²⁺ exchange in hypoxia-related acute astrocyte death. Glia 49: 143–152, 2005.[CrossRef][Web of Science][Medline]
28. Boron WF. Control of intracellular pH. In: The Kidney: Physiology and Pathophysiology (2nd ed.), edited by Seldin DW and Giebish G. New York: Raven, 1992, p. 219–264.
29. Bortner CD and Cidlowski JA. A necessary role for cell shrinkage in apoptosis. Biochem Pharmacol 56: 1549–1559, 1998.[CrossRef][Web of Science][Medline]
30. Bourikas D, Kaloyianni M, Bougoulia M, Zolota Z, and Koliakos G. Modulation of the Na⁺/H⁺ antiport activity by adrenaline on erythrocytes from normal and obese individuals. Mol Cell Endocrinol 205: 141–150, 2003.[CrossRef][Web of Science][Medline]
31. Bourke RS, Kimelberg HK, Nelson LR, Barron KD, Auen EL, Popp AJ, and Waldman JB. Biology of glial swelling in experimental brain edema. Adv Neurol 28: 99–109, 1980.[Medline]
32. Breitwieser GE, Altamirano AA, and Russell JM. Osmotic stimulation of Na⁺-K⁺-2Cl^– cotransport in squid giant axon is [Cl^–]_i dependent. Am J Physiol Cell Physiol 258: C749–C753, 1990.[Abstract/Free Full Text]
33. Brillault J and O'Donnell ME. Effects of hypoxia and vasopressin on cerebral microvascular endothelial intracellular volume (Abstract). FASEB J 19: A809, 2005.
34. Browe DM and Baumgarten CM. Stretch of ₁ integrin activates an outwardly rectifying chloride current via FAK and Src in rabbit ventricular myocytes. J Gen Physiol 122: 689–702, 2003.[Abstract/Free Full Text]
35. Brunner F and Opie LH. Role of endothelin-A receptors in ischemic contracture and reperfusion injury. Circulation 97: 391–398, 1998.[Abstract/Free Full Text]
36. Burg MB. Response of renal inner medullary epithelial cells to osmotic stress. Comp Biochem Physiol A Mol Integr Physiol 133: 661–666, 2002.[CrossRef][Medline]
37. Cala PM. Volume regulation by Amphiuma red blood cells. The membrane potential and its implications regarding the nature of the ion-flux pathways. J Gen Physiol 76: 683–708, 1980.[Abstract/Free Full Text]
38. Cala PM, Anderson SE, and Cragoe EJ Jr. Na/H exchange-dependent cell volume and pH regulation and disturbances. Comp Biochem Physiol A 90: 551–555, 1988.
39. Cala PM, Maldonado H, and Anderson SE. Cell volume and pH regulation by the Amphiuma red blood cell: a model for hypoxia-induced cell injury. Comp Biochem Physiol Comp Physiol 102: 603–608, 1992.[Medline]
40. Cala PM and Maldonado HM. pH regulatory Na/H exchange by Amphiuma red blood cells. J Gen Physiol 103: 1035–1053, 1994.[Abstract/Free Full Text]
41. Canessa M, Fabry ME, Suzuka SM, Morgan K, and Nagel RL. Na⁺/H⁺ exchange is increased in sickle cell anemia and young normal red cells. J Membr Biol 116: 107–115, 1990.[CrossRef][Web of Science][Medline]
42. Carvajal K and Moreno-Sanchez R. Heart metabolic disturbances in cardiovascular diseases. Arch Med Res 34: 89–99, 2003.[CrossRef][Web of Science][Medline]
43. Cassel D, Katz M, and Rotman M. Depletion of cellular ATP inhibits Na⁺/H⁺ antiport in cultured human cells. Modulation of the regulatory effect of intracellular protons on the antiporter activity. J Biol Chem 261: 5460–5466, 1986.[Abstract/Free Full Text]
44. Chakrabarti S, Hoque AN, and Karmazyn M. A rapid ischemia-induced apoptosis in isolated rat hearts and its attenuation by the sodium-hydrogen exchange inhibitor HOE 642 (cariporide). J Mol Cell Cardiol 29: 3169–3174, 1997.[CrossRef][Web of Science][Medline]
45. Chassande O, Frelin C, Farahifar D, Jean T, and Lazdunski M. The Na⁺/K⁺/Cl^– cotransport in C6 glioma cells. Properties and role in volume regulation. Eur J Biochem 171: 425–433, 1988.[Web of Science][Medline]
46. Chattou S, Coulombe A, Diacono J, Le Grand B, John G, and Feuvray D. Slowly inactivating component of sodium current in ventricular myocytes is decreased by diabetes and partially inhibited by known Na⁺/H⁺ exchange blockers. J Mol Cell Cardiol 32: 1181–1192, 2000.[CrossRef][Web of Science][Medline]
47. Chen H, Luo J, Kintner DB, Shull GE, and Sun D. Na⁺-dependent chloride transporter (NKCC1)-null mice exhibit less gray and white matter damage after focal cerebral ischemia. J Cereb Blood Flow Metab 25: 54–66, 2005.[CrossRef][Web of Science][Medline]
48. Chesler M. Regulation and modulation of pH in the brain. Physiol Rev 83: 1183–1221, 2003.[Abstract/Free Full Text]
49. Clarkson K, Kieffer JD, and Currie S. Exhaustive exercise and the cellular stress response in rainbow trout, Oncorhynchus mykiss. Comp Biochem Physiol A Mol Integr Physiol 140: 225–232, 2005.[CrossRef][Medline]
50. Comporti M. Introduction-serial review: iron and cellular redox status. Free Radic Biol Med 32: 565–567, 2002.[CrossRef][Web of Science][Medline]
51. Coupaye-Gerard B, Bookstein C, Duncan P, Chen XY, Smith PR, Musch M, Ernst SA, Chang EB, and Kleyman TR. Biosynthesis and cell surface delivery of the NHE1 isoform of Na⁺/H⁺ exchanger in A6 cells. Am J Physiol Cell Physiol 271: C1639–C1645, 1996.[Abstract/Free Full Text]
52. Cross HR, Radda GK, and Clarke K. The role of Na⁺/K⁺ ATPase activity during low flow ischemia in preventing myocardial injury: a 31P, 23Na and 87Rb NMR spectroscopic study. Magn Reson Med 34: 673–685, 1995.[Web of Science][Medline]
53. Crowe WE, Altamirano J, Huerto L, and Alvarez-Leefmans FJ. Volume changes in single N1E-115 neuroblastoma cells measured with a fluorescent probe. Neuroscience 69: 283–296, 1995.[CrossRef][Web of Science][Medline]
54. Cserr HF, DePasquale M, Nicholson C, Patlak CS, Pettigrew KD, and Rice ME. Extracellular volume decreases while cell volume is maintained by ion uptake in rat brain during acute hypernatremia. J Physiol 442: 277–295, 1991.[Abstract/Free Full Text]
55. Cserr HF, DePasquale M, Patlak CS, and Pullen RGL. Convection of cerebral interstitial fluid and its role in brain volume regulation. Ann NY Acad Sci 481: 123–134, 1986.[Web of Science][Medline]
56. Culman J, Blume A, Gohlke P, and Unger T. The renin-angiotensin system in the brain: possible therapeutic implications for AT₁-receptor blockers. J Hum Hypertens 16, Suppl 3: S64–S70, 2002.
57. Darman RB, Flemmer A, and Forbush B. Modulation of ion transport by direct targeting of protein phosphatase type 1 to the Na-K-Cl cotransporter. J Biol Chem 276: 34359–34362, 2001.[Abstract/Free Full Text]
58. Davies MJ, Bland JM, Hangartner JR, Angelini A, and Thomas AC. Factors influencing the presence or absence of acute coronary artery thrombi in sudden ischaemic death. Eur Heart J 10: 203–208, 1989.[Abstract/Free Full Text]
59. Delpire E. Cation-chloride cotransporters in neuronal communication. News Physiol Sci 15: 309–312, 2000.[Abstract/Free Full Text]
60. Delpire E, Lu J, England R, Dull C, and Thorne T. Deafness and imbalance associated with inactivation of the secretory Na-K-2Cl co-transporter. Nat Genet 22: 192–195, 1999.[CrossRef][Web of Science][Medline]
61. Demaurex N, Romanek RR, Orlowski J, and Grinstein S. ATP dependence of Na+/H+ exchange. Nucleotide specificity and assessment of the role of phospholipids. J Gen Physiol 109: 117–128, 1997.[Abstract/Free Full Text]
62. Dickinson LD and Betz AL. Attenuated development of ischemic brain edema in vasopressin-deficient rats. J Cereb Blood Flow Metab 12: 681–690, 1992.[Web of Science][Medline]
63. Dowd BF and Forbush B. PASK (proline-alanine-rich STE20-related kinase), a regulatory kinase of the Na-K-Cl cotransporter (NKCC1). J Biol Chem 278: 27347–27353, 2003.[Abstract/Free Full Text]
64. Drew C, Ball V, Robinson H, Clive EJ, and Gibson JS. Oxygen sensitivity of red cell membrane transporters revisited. Bioelectrochemistry 62: 153–158, 2004.[CrossRef][Web of Science][Medline]
65. Drewnowska K and Baumgarten CM. Regulation of cellular volume in rabbit ventricular myocytes: bumetanide, chlorothiazide, and ouabain. Am J Physiol Cell Physiol 260: C122–C131, 1991.[Abstract/Free Full Text]
66. Elliott AC, Smith GL, Eisner DA, and Allen DG. Metabolic changes during ischaemia and their role in contractile failure in isolated ferret hearts. J Physiol 454: 467–490, 1992.[Abstract/Free Full Text]
67. Engelhardt S, Hein L, Keller U, Klambt K, and Lohse MJ. Inhibition of Na⁺/H⁺ exchange prevents hypertrophy, fibrosis, and heart failure in ₁-adrenergic receptor transgenic mice. Circ Res 90: 814–819, 2002.[Abstract/Free Full Text]
68. Ennis SR, Ren XD, and Betz AL. Mechanisms of sodium transport at the blood-brain barrier studied with in situ perfusion of rat brain. J Neurochem 66: 756–763, 1996.[Web of Science][Medline]
69. Eriksson PS, Nilsson M, Wagberg M, Ronnback L, and Hansson E. Volume regulation of single astroglial cells in primary culture. Neurosci Lett 143: 195–199, 1992.[CrossRef][Web of Science][Medline]
70. Estrada V, Tellez MJ, Moya J, Fernandez-Durango R, Egido J, and Fernandez Cruz AF. High plasma levels of endothelin-1 and atrial natriuretic peptide in patients with acute ischemic stroke. Am J Hypertens 7: 1085–1089, 1994.[Web of Science][Medline]
71. Falck G, Schjott J, Bruvold M, Krane J, Skarra S, and Jynge P. Hyperosmotic perfusion of the beating rat heart and the role of the Na⁺/K⁺/2Cl^– cotransporter and the Na⁺/H⁺ exchanger. Basic Res Cardiol 95: 19–27, 2000.[CrossRef][Web of Science][Medline]
72. Farfel Z and Cohen Z. Adenylate cyclase in the maturing human reticulocyte: selective loss of the catalytic unit, but not of the receptor-cyclase coupling protein. Eur J Clin Invest 14: 79–82, 1984.[Web of Science][Medline]
73. Ferrer I, Friguls B, Dalfo E, and Planas AM. Early modifications in the expression of mitogen-activated protein kinase (MAPK/ERK), stress-activated kinases SAPK/JNK and p38, and their phosphorylated substrates following focal cerebral ischemia. Acta Neuropathol (Berl) 105: 425–437, 2003.[Medline]
74. Fiers W, Beyaert R, Declercq W, and Vandenabeele P. More than one way to die: apoptosis, necrosis and reactive oxygen damage. Oncogene 18: 7719–7730, 1999.[CrossRef][Web of Science][Medline]
75. Fievet B, Motais R, and Thomas S. Role of adrenergic-dependent H⁺ release from red cells in acidosis induced by hypoxia in trout. Am J Physiol Regul Integr Comp Physiol 252: R269–R275, 1987.[Abstract/Free Full Text]
76. Fisher AB, Chien S, Barakat AI, and Nerem RM. Endothelial cellular response to altered shear stress. Am J Physiol Lung Cell Mol Physiol 281: L529–L533, 2001.[Abstract/Free Full Text]
77. Flagella M, Clarke LL, Miller ML, Erway LC, Giannella RA, Andringa A, Gawenis LR, Kramer J, Duffy JJ, Doetschman T, Lorenz JN, Yamoah EN, Cardell EL, and Shull GE. Mice lacking the basolateral Na-K-2Cl cotransporter have impaired epithelial chloride secretion and are profoundly deaf. J Biol Chem 274: 26946–26955, 1999.[Abstract/Free Full Text]
78. Flatman PW. Regulation of Na-K-2Cl cotransport by phosphorylation and protein-protein interactions. Biochim Biophys Acta 1566: 140–151, 2002.[Medline]
79. Flatman PW. Activation of ferret erythrocyte Na⁺-K⁺-2Cl^– cotransport by deoxygenation. J Physiol 563: 421–431, 2005.[Abstract/Free Full Text]
80. Fliegel L and Dyck JR. Molecular biology of the cardiac sodium/hydrogen exchanger. Cardiovasc Res 29: 155–159, 1995.[CrossRef][Web of Science][Medline]
81. Foroutan S, Brillault J, Forbush B, and O'Donnell ME. Moderate to severe ischemic conditions increase activity and phosphorylation of the cerebral microvascular endothelial cell Na-K-Cl cotransporter. Am J Physiol Cell Physiol 289: C1492–C1501, 2005.[Abstract/Free Full Text]
82. Frangogiannis NG, Smith CW, and Entman ML. The inflammatory response in myocardial infarction. Cardiovasc Res 53: 31–47, 2002.[Abstract/Free Full Text]
83. Franklin CC, Turner JT, and Kim HD. Regulation of Na⁺/K⁺/Cl^– cotransport and [³H]bumetanide binding site density by phorbol esters in HT29 cells. J Biol Chem 264: 6667–6673, 1989.[Abstract/Free Full Text]
84. Frelin C, Chassande O, and Lazdunski M. Biochemical characterization of the Na⁺/K⁺/Cl^– co-transport in chick cardiac cells. Biochem Biophys Res Commun 134: 326–331, 1986.[CrossRef][Web of Science][Medline]
85. Fukushima T, Waddell TK, Grinstein S, Goss GG, Orlowski J, and Downey GP. Na⁺/H⁺ exchange activity during phagocytosis in human neutrophils: role of Fcgamma receptors and tyrosine kinases. J Cell Biol 132: 1037–1052, 1996.[Abstract/Free Full Text]
86. Fung ML, Croning MD, and Haddad GG. Sodium homeostasis in rat hippocampal slices during oxygen and glucose deprivation: role of voltage-sensitive sodium channels. Neurosci Lett 275: 41–44, 1999.[CrossRef][Web of Science][Medline]
87. Gagnon KB, England R, and Delpire E. Volume sensitivity of cation-Cl^– cotransporters is modulated by the interaction of two kinases: Ste20-related proline-alanine-rich kinase and WNK4. Am J Physiol Cell Physiol 290: C134–C142, 2006.[Abstract/Free Full Text]
88. Gerelsaikhan T and Turner RJ. Transmembrane topology of the secretory Na+-K+-2Cl- cotransporter NKCC1 studied by in vitro translation. J Biol Chem 275: 40471–40477, 2000.[Abstract/Free Full Text]
89. Gibson JS, Cossins AR, and Ellory JC. Oxygen-sensitive membrane transporters in vertebrate red cells. J Exp Biol 203: 1395–1407, 2000.[Abstract]
90. Goldberg MP and Choi DW. Combined oxygen and glucose deprivation in cortical cell culture: calcium-dependent and calcium-independent mechanisms of neuronal injury. J Neurosci 13: 3510–3524, 1993.[Abstract]
91. Goldhaber JI and Weiss JN. Oxygen free radicals and cardiac reperfusion abnormalities. Hypertension 20: 118–127, 1992.[Abstract/Free Full Text]
92. Goodwin GW, Ahmad F, Doenst T, and Taegtmeyer H. Energy provision from glycogen, glucose, and fatty acids on adrenergic stimulation of isolated working rat hearts. Am J Physiol Heart Circ Physiol 274: H1239–H1247, 1998.[Abstract/Free Full Text]
93. Gozal E, Sachleben LR Jr, Rane MJ, Vega C, and Gozal D. Mild sustained and intermittent hypoxia induce apoptosis in PC-12 cells via different mechanisms. Am J Physiol Cell Physiol 288: C535–C542, 2005.[Abstract/Free Full Text]
94. Graham RM, Frazier DP, Thompson JW, Haliko S, Li H, Wasserlauf BJ, Spiga MG, Bishopric NH, and Webster KA. A unique pathway of cardiac myocyte death caused by hypoxia-acidosis. J Exp Biol 207: 3189–3200, 2004.[Abstract/Free Full Text]
95. Greger R, Schlatter E, Wang F, and Forrest JN Jr. Mechanism of NaCl secretion in rectal gland tubules of spiny dogfish (Squalus acanthias). III. Effects of stimulation of secretion by cyclic AMP. Pflügers Arch 402: 376–384, 1984.[CrossRef][Web of Science][Medline]
96. Grinstein S, Cohen S, Goetz JD, and Rothstein A. Na⁺/H⁺ exchange in volume regulation and cytoplasmic pH homeostasis in lymphocytes. Fed Proc 44: 2508–2512, 1985.[Web of Science][Medline]
97. Grinstein S, Woodside M, Waddell TK, Downey GP, Orlowski J, Pouyssegur J, Wong DC, and Foskett JK. Focal localization of the NHE-1 isoform of the Na⁺/H⁺ antiport: assessment of effects on intracellular pH. EMBO J 12: 5209–5218, 1993.[Web of Science][Medline]
98. Grinwald PM and Brosnahan C. Sodium imbalance as a cause of calcium overload in post-hypoxic reoxygenation injury. J Mol Cell Cardiol 19: 487–495, 1987.[Web of Science][Medline]
99. Gu XQ, Yao H, and Haddad GG. Increased neuronal excitability and seizures in the Na⁺/H⁺ exchanger null mutant mouse. Am J Physiol Cell Physiol 281: C496–C503, 2001.[Abstract/Free Full Text]
100. Gumina RJ, Moore J, Schelling P, Beier N, and Gross GJ. Na⁺/H⁺ exchange inhibition prevents endothelial dysfunction after I/R injury. Am J Physiol Heart Circ Physiol 281: H1260–H1266, 2001.[Abstract/Free Full Text]
101. Haas M, and Forbush B, III. The Na-K-Cl cotransporter of secretory epithelia. Annu Rev Physiol 62: 515–534, 2000.[CrossRef][Web of Science][Medline]
102. Haddad JJ. Hypoxia and the regulation of mitogen-activated protein kinases: gene transcription and the assessment of potential pharmacologic therapeutic interventions. Int Immunopharmacol 4: 1249–1285, 2004.[CrossRef][Web of Science][Medline]
103. Hansen AJ. Effect of anoxia on ion distribution in the brain. Physiol Rev 65: 101–148, 1985.[Free Full Text]
104. Hisamitsu T, Pang T, Shigekawa M, and Wakabayashi S. Dimeric interaction between the cytoplasmic domains of the Na⁺/H⁺ exchanger NHE1 revealed by symmetrical intermolecular cross-linking and selective co-immunoprecipitation. Biochemistry 43: 11135–11143, 2004.[CrossRef][Medline]
105. Ho HS, Liu H, Cala PM, and Anderson SE. Hypertonic perfusion inhibits intracellular Na and Ca accumulation in hypoxic myocardium. Am J Physiol Cell Physiol 278: C953–C964, 2000.[Abstract/Free Full Text]
106. Hoffmann EK and Dunham PB. Membrane mechanisms and intracellular signalling in cell volume regulation. Int Rev Cytol 161: 173–262, 1995.[Web of Science][Medline]
107. Hoffmann EK and Pedersen SF. Sensors and signal transduction in the activation of cell volume regulatory ion transport systems. Contrib Nephrol 123: 50–78, 1998.[Web of Science][Medline]
108. Holt ME, King SA, Cala PM, and Pedersen SF. Regulation of the Pleuronectes americanus Na⁺/H⁺ exchanger, paNHE1, by osmotic shrinkage, adrenergic stimuli, and inhibition of Ser/Thr protein phosphatases. Cell Biochem Biophys. In press.
109. Horikawa N, Kuribayashi Y, Itoh N, Nishioka M, Matsui K, Kawamura N, and Ohashi N. Na⁺/H⁺ exchange inhibitor SM-20220 improves endothelial dysfunction induced by ischemia-reperfusion. Jpn J Pharmacol 85: 271–277, 2001.[CrossRef][Medline]
110. Howarth F, Qureshi M, and White E. Effects of hyperosmotic shrinking on ventricular myocyte shortening and intracellular Ca²⁺ in streptozotocin-induced diabetic rats. Pflügers Arch 444: 446–451, 2002.[CrossRef][Web of Science][Medline]
111. Hoyt KR, Arden SR, Aizenman E, and Reynolds IJ. Reverse Na⁺/Ca²⁺ exchange contributes to glutamate-induced intracellular Ca²⁺ concentration increases in cultured rat forebrain neurons. Mol Pharmacol 53: 742–749, 1998.[Abstract/Free Full Text]
112. Hsu P, Haffner J, Albuquerque ML, and Leffler CW. pH_i in piglet cerebral microvascular endothelial cells: recovery from an acid load. Proc Soc Exp Biol Med 212: 256–262, 1996.[CrossRef][Medline]
113. Hua Y, Keep RF, Hoff JT, and Xi G. Thrombin preconditioning attenuates brain edema induced by erythrocytes and iron. J Cereb Blood Flow Metab 23: 1448–1454, 2003.[CrossRef][Web of Science][Medline]
114. Hume JR and Harvey RD. Chloride conductance pathways in heart. Am J Physiol Cell Physiol 261: C399–C412, 1991.[Abstract/Free Full Text]
115. Ihara M, Urata H, Shirai K, Ideishi M, Hoshino F, Suzumiya J, Kikuchi M, and Arakawa K. High cardiac angiotensin II-forming activity in infarcted and non-infarcted human myocardium. Cardiology 94: 247–253, 2000.[CrossRef][Web of Science][Medline]
116. Ikehara T, Yamaguchi H, Hosokawa K, and Miyamoto H. Kinetic mechanism of ATP action in Na⁺-K⁺-Cl^– cotransport of HeLa cells determined by Rb+ influx studies. Am J Physiol Cell Physiol 258: C599–C609, 1990.[Abstract/Free Full Text]
117. Imahashi K, Kusuoka H, Hashimoto K, Yoshioka J, Yamaguchi H, and Nishimura T. Intracellular sodium accumulation during ischemia as the substrate for reperfusion injury. Circ Res 84: 1401–1406, 1999.[Abstract/Free Full Text]
118. Ising H, Gunther T, Bertschat F, Ibe K, Stoboy V, and Heldman E. Alterations of electrolytes in serum and erythrocytes after myocardial infarction. Magnesium 6: 192–200, 1987.[Web of Science][Medline]
119. Ito N, Bartunek J, Spitzer KW, and Lorell BH. Effects of the nitric oxide donor sodium nitroprusside on intracellular pH and contraction in hypertrophied myocytes. Circulation 95: 2303–2311, 1997.[Abstract/Free Full Text]
120. Jaeschke H. Molecular mechanisms of hepatic ischemia-reperfusion injury and preconditioning. Am J Physiol Gastrointest Liver Physiol 284: G15–G26, 2003.[Abstract/Free Full Text]
121. Jakubovicz DE and Klip A. Lactic acid-induced swelling in C6 glial cells via Na⁺/H⁺ exchange. Brain Res 485: 215–224, 1989.[CrossRef][Web of Science][Medline]
122. Jalowy A, Schulz R, and Heusch G. AT₁ receptor blockade in experimental myocardial ischemia/reperfusion. J Am Soc Nephrol 10, Suppl 11: S129–S136, 1999.[Web of Science][Medline]
123. Jennings ML, Douglas SM, and McAndrew PE. Amiloride-sensitive sodium-hydrogen exchange in osmotically shrunken rabbit red blood cells. Am J Physiol Cell Physiol 251: C32–C40, 1986.[Abstract/Free Full Text]
124. Jorgensen NK, Petersen SF, Damgaard I, Schousboe A, and Hoffmann EK. Increases in [Ca²⁺]_i and changes in intracellular pH during chemical anoxia in mouse neocortical neurons in primary culture. J Neurosci Res 56: 358–370, 1999.[CrossRef][Web of Science][Medline]
125. Jung F, Kessler H, Pindur G, Sternitzky R, and Franke RP. Intramuscular oxygen partial pressure in the healthy during exercise. Clin Hemorheol Microcirc 21: 25–33, 1999.[Web of Science][Medline]
126. Kaila K, Panula P, Karhunen T, and Heinonen E. Fall in intracellular pH mediated by GABAA receptors in cultured rat astrocytes. Neurosci Lett 126: 9–12, 1991.[CrossRef][Web of Science][Medline]
127. Kalaria RN, Premkumar DR, Lin CW, Kroon SN, Bae JY, Sayre LM, and LaManna JC. Identification and expression of the Na⁺/H⁺ exchanger in mammalian cerebrovascular and choroidal tissues: characterization by amiloride-sensitive [3H]MIA binding and RT-PCR analysis. Brain Res Mol Brain Res 58: 178–187, 1998.[Medline]
128. Kanaka C, Ohno K, Okabe A, Kuriyama K, Itoh T, Fukuda A, and Sato K. The differential expression patterns of messenger RNAs encoding K-Cl cotransporters (KCC1,2) and Na-K-2Cl cotransporter (NKCC1) in the rat nervous system. Neuroscience 104: 933–946, 2001.[CrossRef][Web of Science][Medline]
129. Kang TC, An SJ, Park SK, Hwang IK, Yoon DK, Shin HS, and Won MH. Changes in Na⁺-K⁺-Cl^– cotransporter immunoreactivity in the gerbil hippocampus following transient ischemia. Neurosci Res 44: 249–254, 2002.[CrossRef][Web of Science][Medline]
130. Kato H, Kogure K, Sakamoto N, and Watanabe T. Greater disturbance of water and ion homeostasis in the periphery of experimental focal cerebral ischemia. Exp Neurol 96: 118–126, 1987.[CrossRef][Web of Science][Medline]
131. Kawai N, McCarron RM, and Spatz M. Na⁺-K⁺-Cl^– cotransport system in brain capillary endothelial cells: response to endothelin and hypoxia. Neurochem Res 21: 1259–1266, 1996.[Web of Science][Medline]
132. Khandoudi N, Albadine J, Robert P, Krief S, Berrebi-Bertrand I, Martin X, Bevensee MO, Boron WF, and Bril A. Inhibition of the cardiac electrogenic sodium bicarbonate cotransporter reduces ischemic injury. Cardiovasc Res 52: 387–396, 2001.[Abstract/Free Full Text]
133. Khandoudi N, Ho J, and Karmazyn M. Role of Na⁺/H⁺ exchange in mediating effects of endothelin-1 on normal and ischemic/reperfused hearts. Circ Res 75: 369–378, 1994.[Abstract/Free Full Text]
134. Kim JA, Kang YY, and Lee YS. Activation of Na⁺,K⁺,Cl^– cotransport mediates intracellular Ca²⁺ increase and apoptosis induced by Pinacidil in HepG2 human hepatoblastoma cells. Biochem Biophys Res Commun 281: 511–519, 2001.[CrossRef][Web of Science][Medline]
135. Kimelberg HK. Cell swelling in cerebral ischemia. In: Cerebral Ischemia: Molecular and Cellular Pathophysiology, edited by Walz W and Totawa HJ. Clifton, NJ: Humana, 1999, p. 45–68.
136. Kintner DB, Look A, Shull GE, and Sun D. Stimulation of astrocyte Na⁺/H⁺ exchange activity in response to in vitro ischemia depends in part on activation of ERK1/2. Am J Physiol Cell Physiol 289: C934–C945, 2005.[Abstract/Free Full Text]
137. Kintner DB, Su G, Lenart BA, Ballard AJ, Meyer JW, Ng LL, Shull GE, and Sun D. Increased tolerance to oxygen and glucose deprivation in astrocytes from Na⁺/H⁺ exchanger isoform 1 null mice. Am J Physiol Cell Physiol 287: C12–C21, 2004.[Abstract/Free Full Text]
138. Knight DR, Smith AH, Flynn DM, MacAndrew JT, Ellery SS, Kong JX, Marala RB, Wester RT, Guzman-Perez A, Hill RJ, Magee WP, and Tracey WR. A novel sodium-hydrogen exchanger isoform-1 inhibitor, zoniporide, reduces ischemic myocardial injury in vitro and in vivo. J Pharmacol Exp Ther 297: 254–259, 2001.[Abstract/Free Full Text]
139. Kochanek PM and Hallenbeck JM. Polymorphonuclear leukocytes and monocytes/macrophages in the pathogenesis of cerebral ischemia and stroke. Stroke 23: 1367–1379, 1992.[Abstract/Free Full Text]
140. Kregenow FM. The response of duck erythrocytes to hypertonic media. Further evidence for a volume-controlling mechanism. J Gen Physiol 58: 396–412, 1971.[Abstract/Free Full Text]
141. Kregenow FM, Caryk T, and Siebens AW. Further studies of the volume-regulatory response of Amphiuma red cells in hypertonic media. Evidence for amiloride-sensitive Na/H exchange. J Gen Physiol 86: 565–584, 1985.[Abstract/Free Full Text]
142. Kristian T and Siesjo BK. Calcium-related damage in ischemia. Life Sci 59: 357–367, 1996.[CrossRef][Web of Science][Medline]
143. Kusuhara M, Takahashi E, Peterson TE, Abe J, Ishida M, Han J, Ulevitch R, and Berk BC. p38 Kinase is a negative regulator of angiotensin II signal transduction in vascular smooth muscle cells: effects on Na⁺/H⁺ exchange and ERK1/2. Circ Res 83: 824–831, 1998.[Web of Science][Medline]
144. Ladecola C. Mechanisms of cerebral ischemic damage. In: Cerebral Ischemia: Molecular and Cellular Pathophysiology, edited by Walz W and Totawa HJ. Clifton, NJ: Humana, 1999, p. 3–34.
145. Ladilov YV, Siegmund B, and Piper HM. Protection of reoxygenated cardiomyocytes against hypercontracture by inhibition of Na⁺/H⁺ exchange. Am J Physiol Heart Circ Physiol 268: H1531–H1539, 1995.[Abstract/Free Full Text]
146. Lagadic-Gossmann D and Vaughan-Jones RD. Coupling of dual acid extrusion in the guinea-pig isolated ventricular myocyte to ₁- and -adrenoceptors. J Physiol 464: 49–73, 1993.[Abstract/Free Full Text]
147. Lam TI, Anderson SE, Glaser N, and O'Donnell ME. Bumetanide reduces cerebral edema formation in rats with diabetic ketoacidosis. Diabetes 54: 510–516, 2005.[Abstract/Free Full Text]
148. Lang KS, Duranton C, Poehlmann H, Myssina S, Bauer C, Lang F, Wieder T, and Huber SM. Cation channels trigger apoptotic death of erythrocytes. Cell Death Differ 10: 249–256, 2003.[CrossRef][Web of Science][Medline]
149. Lazdunski M, Frelin C, and Vigne P. The sodium/hydrogen exchange system in cardiac cells: its biochemical and pharmacological properties and its role in regulating internal concentrations of sodium and internal pH. J Mol Cell Cardiol 17: 1029–1042, 1985.[Web of Science][Medline]
150. Lenart B, Kintner DB, Shull GE, and Sun D. Na-K-Cl cotransporter-mediated intracellular Na⁺ accumulation affects Ca²⁺ signaling in astrocytes in an in vitro ischemic model. J Neurosci 24: 9585–9597, 2004.[Abstract/Free Full Text]
151. Leung S, O'Donnell ME, Martinez A, and Palfrey HC. Regulation by nerve growth factor and protein phosphorylation of Na/K/2Cl cotransport and cell volume in PC12 cells. J Biol Chem 269: 10581–10589, 1994.[Abstract/Free Full Text]
152. Levi R and Smith NC. Histamine H₃-receptors: a new frontier in myocardial ischemia. J Pharmacol Exp Ther 292: 825–830, 2000.[Abstract/Free Full Text]
153. Lindinger MI and Grudzien SP. Exercise-induced changes in plasma composition increase erythrocyte Na⁺-K⁺-ATPase, but not Na⁺-K⁺-2Cl^– cotransporter, activity to stimulate net and unidirectional K⁺ transport in humans. J Physiol 553: 987–997, 2003.[Abstract/Free Full Text]
154. Lipton P. Ischemic cell death in brain neurons. Physiol Rev 79: 1431–1568, 1999.[Abstract/Free Full Text]
155. Liu H, Cala PM, and Anderson SE. Ethylisopropylamiloride diminishes changes in intracellular Na, Ca and pH in ischemic newborn myocardium. J Mol Cell Cardiol 29: 2077–2086, 1997.[CrossRef][Web of Science][Medline]
156. Liu H, Cala PM, and Anderson SE. Ischemic preconditioning: effects on pH, Na and Ca in newborn rabbit hearts during ischemia/reperfusion. J Mol Cell Cardiol 30: 685–697, 1998.[CrossRef][Web of Science][Medline]
157. Logue SE, Gustafsson AB, Samali A, and Gottlieb RA. Ischemia/reperfusion injury at the intersection with cell death. J Mol Cell Cardiol 38: 21–33, 2005.[CrossRef][Web of Science][Medline]
158. Lou JM, Garay RP, Gimenez I, Escanero JF, and Alda JO. Isoosmotic shrinkage by self-stimulated outward Na-K-Cl cotransport in quail erythrocytes. Pflügers Arch 447: 64–70, 2003.[CrossRef][Web of Science][Medline]
159. Lowe TE, Brill RW, and Cousins KL. Responses of the red blood cells from two high-energy-demand teleosts, yellowfin tuna (Thunnus albacares) and skipjack tuna (Katsuwonus pelamis), to catecholamines. J Comp Physiol [B] 168: 405–418, 1998.[CrossRef][Medline]
160. Lusardi TA, Rangan J, Sun D, Smith DH, and Meaney DF. A device to study the initiation and propagation of calcium transients in cultured neurons after mechanical stretch. Ann Biomed Eng 32: 1546–1558, 2004.[CrossRef][Web of Science][Medline]
161. Lytle C. Activation of the avian erythrocyte Na-K-Cl cotransport protein by cell shrinkage, cAMP, fluoride, and calyculin-A involves phosphorylation at common sites. J Biol Chem 272: 15069–15077, 1997.[Abstract/Free Full Text]
162. Ma E and Haddad GG. Expression and localization of Na⁺/H⁺ exchangers in rat central nervous system. Neuroscience 79: 591–603, 1997.[CrossRef][Web of Science][Medline]
163. MacVicar BA, Feighan D, Brown A, and Ransom B. Intrinsic optical signals in the rat optic nerve: role for K⁺ uptake via NKCC1 and swelling of astrocytes. Glia 37: 114–123, 2002.[CrossRef][Web of Science][Medline]
164. Maczewski M and Beresewicz A. Role of nitric oxide and free radicals in cardioprotection by blocking Na⁺/H⁺ and Na⁺/Ca²⁺ exchange in rat heart. Eur J Pharmacol 461: 139–147, 2003.[CrossRef][Web of Science][Medline]
165. Mairbaurl H and Hoffman JF. Internal magnesium, 2,3-diphosphoglycerate, and the regulation of the steady-state volume of human red blood cells by the Na/K/2Cl cotransport system. J Gen Physiol 99: 721–746, 1992.[Abstract/Free Full Text]
166. Mairbaurl H, Schulz S, and Hoffman JF. Cation transport and cell volume changes in maturing rat reticulocytes. Am J Physiol Cell Physiol 279: C1621–C1630, 2000.[Abstract/Free Full Text]
167. Malapert M, Guizouarn H, Fievet B, Jahns R, Garcia-Romeu F, Motais R, and Borgese F. Regulation of Na⁺/H⁺ antiporter in trout red blood cells. J Exp Biol 200: 353–360, 1997.[Abstract]
168. Marklund L, Henriksson R, and Grankvist K. Amphotericin B-induced apoptosis and cytotoxicity is prevented by the Na⁺-K⁺-2Cl^– cotransport blocker bumetanide. Life Sci 66: L319–L324, 2000.
169. Matsuyama S, Llopis J, Deveraux QL, Tsien RY, and Reed JC. Changes in intramitochondrial and cytosolic pH: early events that modulate caspase activation during apoptosis. Nat Cell Biol 2: 318–325, 2000.[CrossRef][Web of Science][Medline]
170. Matthews JB, Smith JA, Tally KJ, Awtrey CS, Nguyen H, Rich J, and Madara JL. Na-K-2Cl cotransport in intestinal epithelial cells. Influence of chloride efflux and F-actin on regulation of cotransporter activity and bumetanide binding. J Biol Chem 269: 15703–15709, 1994.[Abstract/Free Full Text]
171. Mazzoni MC, Intaglietta M, Cragoe EJ Jr, and Arfors KE. Amiloride-sensitive Na⁺ pathways in capillary endothelial cell swelling during hemorrhagic shock. J Appl Physiol 73: 1467–1473, 1992.[Abstract/Free Full Text]
172. McKelvie RS, Jones NL, and Heigenhauser GJ. Effect of progressive incremental exercise and -adrenergic blockade on erythrocyte ion concentrations. Can J Physiol Pharmacol 75: 19–25, 1997.[CrossRef][Web of Science][Medline]
173. McLean LA, Roscoe J, Jorgensen NK, Gorin FA, and Cala PM. Malignant gliomas display altered pH regulation by NHE1 compared with nontransformed astrocytes. Am J Physiol Cell Physiol 278: C676–C688, 2000.[Abstract/Free Full Text]
174. McLean LA, Zia S, Gorin FA, and Cala PM. Cloning and expression of the Na⁺/H⁺ exchanger from Amphiuma RBCs: resemblance to mammalian NHE1. Am J Physiol Cell Physiol 276: C1025–C1037, 1999.[Abstract/Free Full Text]
175. McManus ML and Strange K. Acute volume regulation of brain cells in response to hypertonic challenge. Anesthesiology 78: 1132–1137, 1993.[Web of Science][Medline]
176. Meiltz A, Kucera P, de Ribaupierre Y, and Raddatz E. Inhibition of bicarbonate transport protects embryonic heart against reoxygenation-induced dysfunction. J Mol Cell Cardiol 30: 327–335, 1998.[CrossRef][Web of Science][Medline]
177. Melzian D, Scheufler E, Grieshaber M, and Tegtmeier F. Tissue swelling and intracellular pH in the CA1 region of anoxic rat hippocampus. J Neurosci Methods 65: 183–187, 1996.[CrossRef][Web of Science][Medline]
178. Menzies SA, Betz AL, and Hoff JT. Contributions of ions and albumin to the formation and resolution of ischemic brain edema. J Neurosurg 78: 257–266, 1993.[Web of Science][Medline]
179. Messana I, Orlando M, Cassiano L, Pennacchietti L, Zuppi C, Castagnola M, and Giardina B. Human erythrocyte metabolism is modulated by the O₂-linked transition of hemoglobin. FEBS Lett 390: 25–28, 1996.[CrossRef][Web of Science][Medline]
180. Mirabet M, Garcia-Dorado D, Inserte J, Barrabes JA, Lidon RM, Soriano B, Azevedo M, Padilla F, Agullo L, Ruiz-Meana M, Massaguer A, Pizcueta P, and Soler-Soler J. Platelets activated by transient coronary occlusion exacerbate ischemia-reperfusion injury in rat hearts. Am J Physiol Heart Circ Physiol 283: H1134–H1141, 2002.[Abstract/Free Full Text]
181. Misik AJ, Perreault K, Holmes CF, and Fliegel L. Protein phosphatase regulation of Na⁺/H⁺ exchanger isoform I. Biochemistry 44: 5842–5852, 2005.[CrossRef][Medline]
182. Moor AN, Gan XT, Karmazyn M, and Fliegel L. Activation of Na⁺/H⁺ exchanger-directed protein kinases in the ischemic and ischemic-reperfused rat myocardium. J Biol Chem 276: 16113–16122, 2001.[Abstract/Free Full Text]
183. Moor AN, Murtazina R, and Fliegel L. Calcium and osmotic regulation of the Na⁺/H⁺ exchanger in neonatal ventricular myocytes. J Mol Cell Cardiol 32: 925–936, 2000.[CrossRef][Web of Science][Medline]
184. Moore-Hoon ML and Turner RJ. The structural unit of the secretory Na⁺-K⁺-2Cl^– cotransporter (NKCC1) is a homodimer. Biochemistry 39: 3718–3724, 2000.[CrossRef][Medline]
185. Moreau P, d'Uscio LV, Shaw S, Takase H, Barton M, and Luscher TF. Angiotensin II increases tissue endothelin and induces vascular hypertrophy: reversal by ET_A-receptor antagonist. Circulation 96: 1593–1597, 1997.[Abstract/Free Full Text]
186. Motais R, Garcia-Romeu F, and Borgese F. The control of Na⁺/H⁺ exchange by molecular oxygen in trout erythrocytes. A possible role of hemoglobin as a transducer. J Gen Physiol 90: 197–207, 1987.[Abstract/Free Full Text]
187. Mukhin YV, Garnovskaya MN, Ullian ME, and Raymond JR. ERK is regulated by sodium-proton exchanger in rat aortic vascular smooth muscle cells. J Biol Chem 279: 1845–1852, 2004.[Abstract/Free Full Text]
188. Mulkey DK, Henderson RA, III, Ritucci NA, Putnam RW, and Dean JB. Oxidative stress decreases pHi and Na⁺/H⁺ exchange and increases excitability of solitary complex neurons from rat brain slices. Am J Physiol Cell Physiol 286: C940–C951, 2004.[Abstract/Free Full Text]
189. Murphy E, Cross H, and Steenbergen C. Sodium regulation during ischemia versus reperfusion and its role in injury. Circ Res 84: 1469–1470, 1999.[Free Full Text]
190. Murphy E, Perlman M, London RE, and Steenbergen C. Amiloride delays the ischemia-induced rise in cytosolic free calcium. Circ Res 68: 1250–1258, 1991.[Abstract/Free Full Text]
191. Murphy VA and Johanson CE. Na⁺/H⁺ exchange in choroid plexus and CSF in acute metabolic acidosis or alkalosis. Am J Physiol Renal Fluid Electrolyte Physiol 258: F1528–F1537, 1990.[Abstract/Free Full Text]
192. Muzyamba MC, Cossins AR, Gibson JS. Regulation of Na⁺-K⁺-2Cl^– cotransport in turkey red cells: the role of oxygen tension and protein phosphorylation. J Physiol 517: 421–429, 1999.[Abstract/Free Full Text]
193. Myers MG, Norris JW, Hachniski VC, and Sole MJ. Plasma norepinephrine in stroke. Stroke 12: 200–204, 1981.[Abstract/Free Full Text]
194. Myers ML, Farhangkhoee P, and Karmazyn M. Hydrogen peroxide induced impairment of post-ischemic ventricular function is prevented by the sodium-hydrogen exchange inhibitor HOE 642 (cariporide). Cardiovasc Res 40: 290–296, 1998.[Abstract/Free Full Text]
195. Nakamura N, Tanaka S, Teko Y, Mitsui K, and Kanazawa H. Four Na⁺/H⁺ exchanger isoforms are distributed to Golgi and post-Golgi compartments and are involved in organelle pH regulation. J Biol Chem 280: 1561–1572, 2005.[Abstract/Free Full Text]
196. Neumar RW. Molecular mechanisms of ischemic neuronal injury. Ann Emerg Med 36: 483–506, 2000.[Web of Science][Medline]
197. Nikinmaa M. Oxygen and carbon dioxide transport in vertebrate erythrocytes: an evolutionary change in the role of membrane transport. J Exp Biol 200: 369–380, 1997.[Abstract]
198. Nikinmaa M. Oxygen-dependent cellular functions–why fishes and their aquatic environment are a prime choice of study. Comp Biochem Physiol A Mol Integr Physiol 133: 1–16, 2002.[CrossRef][Medline]
199. Nikinmaa M, Bogdanova A, and Lecklin T. Oxygen dependency of the adrenergic Na/H exchange in rainbow trout erythrocytes is diminished by a hydroxyl radical scavenger. Acta Physiol Scand 178: 149–154, 2003.[CrossRef][Web of Science][Medline]
200. Node K, Kitakaze M, Kosaka H, Minamino T, Funaya H, and Hori M. Amelioration of ischemia- and reperfusion-induced myocardial injury by 17-estradiol: role of nitric oxide and calcium-activated potassium channels. Circulation 96: 1953–1963, 1997.[Abstract/Free Full Text]
201. Nylandsted J, Jäättelä M, Hoffmann EK, and Pedersen SF. Heat shock protein 70 inhibits shrinkage-induced programmed cell death via mechanisms independent of effects on cell volume-regulatory membrane transport proteins. Pflügers Arch 449: 175–185, 2004.[CrossRef][Web of Science][Medline]
202. O'Donnell ME. Role of Na-K-Cl cotransport in vascular endothelial cell volume regulation. Am J Physiol Cell Physiol 264: C1316–C1326, 1993.[Abstract/Free Full Text]
203. O'Donnell ME, Duong V, Suvatne J, Foroutan S, and Johnson DM. Arginine vasopressin stimulation of cerebral microvascular endothelial cell Na-K-Cl cotransporter activity is V₁ receptor and [Ca] dependent. Am J Physiol Cell Physiol 289: C283–C292, 2005.[Abstract/Free Full Text]
204. O'Donnell ME, Lam TI, Tran LQ, Foroutan S, and Anderson SE. Estradiol reduces activity of the blood-brain barrier Na-K-Cl cotransporter and decreases edema formation in permanent middle cerebral artery occlusion. J Cereb Blood Flow Metab. In press.
205. O'Donnell ME, Tran L, Lam TI, Liu XB, and Anderson SE. Bumetanide inhibition of the blood-brain barrier Na-K-Cl cotransporter reduces edema formation in the rat middle cerebral artery occlusion model of stroke. J Cereb Blood Flow Metab 24: 1046–1056, 2004.[CrossRef][Web of Science][Medline]
206. O'Neill WC. Physiological significance of volume-regulatory transporters. Am J Physiol Cell Physiol 276: C995–C1011, 1999.[Abstract/Free Full Text]
207. Orlov SN, Kuznetsov SR, Pokudin NI, Tremblay J, and Hamet P. Can we use erythrocytes for the study of the activity of the ubiquitous Na⁺/H⁺ exchanger (NHE-1) in essential hypertension? Am J Hypertens 11: 774–783, 1998.[CrossRef][Web of Science][Medline]
208. Orlov SN, Resink TJ, Bernhardt J, and Buhler FR. Volume-dependent regulation of sodium and potassium fluxes in cultured vascular smooth muscle cells: dependence on medium osmolality and regulation by signalling systems. J Membr Biol 129: 199–210, 1992.[Web of Science][Medline]
209. Orlowski J and Grinstein S. Diversity of the mammalian sodium/proton exchanger SLC9 gene family. Pflügers Arch 447: 549–565, 2004.[CrossRef][Web of Science][Medline]
210. Orlowski J, Kandasamy RA, and Shull GE. Molecular cloning of putative members of the Na/H exchanger gene family. cDNA cloning, deduced amino acid sequence, and mRNA tissue expression of the rat Na/H exchanger NHE-1 and two structurally related proteins. J Biol Chem 267: 9331–9339, 1992.[Abstract/Free Full Text]
211. Otani H, Uchiyama T, Yamamura T, Nakao Y, Hattori R, Ninomiya H, Kido M, Kawaguchi H, Osako M, and Imamura H. Effects of the Na⁺/H⁺ exchange inhibitor cariporide (HOE 642) on cardiac function and cardiomyocyte cell death in rat ischaemic-reperfused heart. Clin Exp Pharmacol Physiol 27: 387–393, 2000.[CrossRef][Web of Science][Medline]
212. Ou-yang Y, Mellergard P, Siesjo BK. Regulation of intracellular pH in single rat cortical neurons in vitro: a microspectrofluorometric study. J Cereb Blood Flow Metab 13: 827–840, 1993.[Web of Science][Medline]
213. Pan J, Singh US, Takahashi T, Oka Y, Palm-Leis A, Herbelin BS, and Baker KM. PKC mediates cyclic stretch-induced cardiac hypertrophy through Rho family GTPases and mitogen-activated protein kinases in cardiomyocytes. J Cell Physiol 202: 536–553, 2005.[CrossRef][Web of Science][Medline]
214. Panet R, Eliash M, Pick M, and Atlan H. Na⁺/K⁺/Cl^– cotransporter activates mitogen-activated protein kinase in fibroblasts and lymphocytes. J Cell Physiol 190: 227–237, 2002.[CrossRef][Web of Science][Medline]
215. Paris S and Pouyssegur J. Growth factors activate the bumetanide-sensitive Na⁺/K⁺/Cl^– cotransport in hamster fibroblasts. J Biol Chem 261: 6177–6183, 1986.[Abstract/Free Full Text]
216. Parker JC, Colclasure GC, and McManus TJ. Coordinated regulation of shrinkage-induced Na/H exchange and swelling-induced [K-Cl] cotransport in dog red cells. Further evidence from activation kinetics and phosphatase inhibition. J Gen Physiol 98: 869–880, 1991.[Abstract/Free Full Text]
217. Parthasarathi K and Lipowsky HH. Capillary recruitment in response to tissue hypoxia and its dependence on red blood cell deformability. Am J Physiol Heart Circ Physiol 277: H2145–H2157, 1999.[Abstract/Free Full Text]
218. Pasantes-Morales H, Cardin V, and Tuz K. Signaling events during swelling and regulatory volume decrease. Neurochem Res 25: 1301–1314, 2000.[CrossRef][Web of Science][Medline]
219. Pasternack M, Voipio J, and Kaila K. Intracellular carbonic anhydrase activity and its role in GABA-induced acidosis in isolated rat hippocampal pyramidal neurones. Acta Physiol Scand 148: 229–231, 1993.[Web of Science][Medline]
220. Pedersen S, Pedersen SF, Nilius B, Lambert IH, and Hoffmann EK. Mechanical stress induces release of ATP from Ehrlich ascites tumor cells. Biochim Biophys Acta 1416: 271–284, 1999.[Medline]
221. Pedersen SF. The Na⁺/H⁺ exchanger NHE1 in stress-induced signal transduction: implications for cell proliferation and cell death. Pflügers Archiv. In press.
222. Pedersen SF and Cala PM. Comparative biology of the ubiquitous Na⁺/H⁺ exchanger, NHE1: lessons from erythrocytes. J Exp Zoolog Part A Comp Exp Biol 301: 569–578, 2004.[Medline]
223. Pedersen SF, Jorgensen NK, Damgaard I, Schousboe A, and Hoffmann EK. Mechanisms of pHi regulation studied in individual neurons cultured from mouse cerebral cortex. J Neurosci Res 51: 431–441, 1998.[CrossRef][Web of Science][Medline]
224. Pedersen SF, Jorgensen NK, and Hoffmann EK. Dynamics of [Ca²⁺]_i and pH_i in Ehrlich ascites tumor cells after Ca²⁺-mobilizing agonists or exposure to hypertonic solution. Pflügers Arch 436: 199–210, 1998.[CrossRef][Web of Science][Medline]
225. Pedersen SF, King SA, Rigor RR, Zhuang Z, Warren JM, and Cala PM. Molecular cloning of NHE1 from winter flounder RBCs: activation by osmotic shrinkage, cAMP, and calyculin A. Am J Physiol Cell Physiol 284: C1561–C1576, 2003.[Abstract/Free Full Text]
226. Pedersen SF, Varming C, Christensen ST, and Hoffmann EK. Mechanisms of activation of NHE by cell shrinkage and by calyculin A in Ehrlich ascites tumor cells. J Membr Biol 189: 67–81, 2002.[CrossRef][Web of Science][Medline]
227. Petrecca K, Atanasiu R, Grinstein S, Orlowski J, and Shrier A. Subcellular localization of the Na⁺/H⁺ exchanger NHE1 in rat myocardium. Am J Physiol Heart Circ Physiol 276: H709–H717, 1999.[Abstract/Free Full Text]
228. Petrov V, Amery A, and Lijnen P. Role of cyclic GMP in atrial-natriuretic-peptide stimulation of erythrocyte Na⁺/H⁺ exchange. Eur J Biochem 221: 195–199, 1994.[Web of Science][Medline]
229. Petty MA and Wettstein JG. Elements of cerebral microvascular ischaemia. Brain Res Brain Res Rev 36: 23–34, 2001.[CrossRef][Medline]
230. Piechotta K, Garbarini N, England R, and Delpire E. Characterization of the interaction of the stress kinase SPAK with the Na⁺-K⁺-2Cl^– cotransporter in the nervous system: evidence for a scaffolding role of the kinase. J Biol Chem 278: 52848–52856, 2003.[Abstract/Free Full Text]
231. Piechotta K, Lu J, and Delpire E. Cation chloride cotransporters interact with the stress-related kinases Ste20-related proline-alanine-rich kinase (SPAK) and oxidative stress response 1 (OSR1). J Biol Chem 277: 50812–50819, 2002.[Abstract/Free Full Text]
232. Pike MM, Luo CS, Clark MD, Kirk KA, Kitakaze M, Madden MC, Cragoe EJ Jr and Pohost GM. NMR measurements of Na⁺ and cellular energy in ischemic rat heart: role of Na⁺-H⁺ exchange. Am J Physiol Heart Circ Physiol 265: H2017–H2026, 1993.[Abstract/Free Full Text]
233. Pilitsis JG, Diaz FG, O'Regan MH, and Phillis JW. Inhibition of Na⁺/H⁺ exchange by SM-20220 attenuates free fatty acid efflux in rat cerebral cortex during ischemia-reperfusion injury. Brain Res 913: 156–158, 2001.[CrossRef][Web of Science][Medline]
234. Plesnila N, Haberstok J, Peters J, Kolbl I, Baethmann A, and Staub F. Effect of lactacidosis on cell volume and intracellular pH of astrocytes. J Neurotrauma 16: 831–841, 1999.[Web of Science][Medline]
235. Plotkin MD, Kaplan MR, Peterson LN, Gullans SR, Hebert SC, and Delpire E. Expression of the Na⁺-K⁺-2Cl^– cotransporter BSC2 in the nervous system. Am J Physiol Cell Physiol 272: C173–C183, 1997.[Abstract/Free Full Text]
236. Pond BB, Galeffi F, Ahrens R, and Schwartz-Bloom RD. Chloride transport inhibitors influence recovery from oxygen-glucose deprivation-induced cellular injury in adult hippocampus. Neuropharmacology 47: 253–262, 2004.[CrossRef][Web of Science][Medline]
237. Poole-Wilson PA and Tones MA. Sodium exchange during hypoxia and on reoxygenation in the isolated rabbit heart. J Mol Cell Cardiol 20, Suppl 2: 15–22, 1988.[Web of Science][Medline]
238. Putney LK, Denker SP, and Barber DL. The changing face of the Na⁺/H⁺ exchanger, NHE1: structure, regulation, and cellular actions. Annu Rev Pharmacol Toxicol 42: 527–552, 2002.[CrossRef][Web of Science][Medline]
239. Raftos JE, Lew VL, and Flatman PW. Refinement and evaluation of a model of Mg²⁺ buffering in human red cells. Eur J Biochem 263: 635–645, 1999.[Web of Science][Medline]
240. Raley-Susman KM, Cragoe EJ Jr, Sapolsky RM, and Kopito RR. Regulation of intracellular pH in cultured hippocampal neurons by an amiloride-insensitive Na⁺/H⁺ exchanger. J Biol Chem 266: 2739–2745, 1991.[Abstract/Free Full Text]
241. Ramasamy R, Payne JA, Whang J, Bergmann SR, and Schaefer S. Protection of ischemic myocardium in diabetics by inhibition of electroneutral Na⁺-K⁺-2Cl^– cotransporter. Am J Physiol Heart Circ Physiol 281: H515–H522, 2001.[Abstract/Free Full Text]
242. Ramasamy R, Zhao P, Gitomer WL, Sherry AD, and Malloy CR. Determination of chloride potential in perfused rat hearts by nuclear magnetic resonance spectroscopy. Am J Physiol Heart Circ Physiol 263: H1958–H1962, 1992.[Abstract/Free Full Text]
243. Rehring TF, Shapiro JI, Cain BS, Meldrum DR, Cleveland JC, Harken AH, and Banerjee A. Mechanisms of pH preservation during global ischemia in preconditioned rat heart: roles for PKC and NHE. Am J Physiol Heart Circ Physiol 275: H805–H813, 1998.[Abstract/Free Full Text]
244. Reid AC, Mackins CJ, Seyedi N, Levi R, and Silver RB. Coupling of angiotensin II AT₁ receptors to neuronal NHE activity and carrier-mediated norepinephrine release in myocardial ischemia. Am J Physiol Heart Circ Physiol 286: H1448–H1454, 2004.[Abstract/Free Full Text]
245. Resnick N, Yahav H, Shay-Salit A, Shushy M, Schubert S, Zilberman LC, and Wofovitz E. Fluid shear stress and the vascular endothelium: for better and for worse. Prog Biophys Mol Biol 81: 177–199, 2003.[CrossRef][Web of Science][Medline]
246. Rich IN, Worthington-White D, Garden OA, and Musk P. Apoptosis of leukemic cells accompanies reduction in intracellular pH after targeted inhibition of the Na⁺/H⁺ exchanger. Blood 95: 1427–1434, 2000.[Abstract/Free Full Text]
247. Rosskopf D. Sodium-hydrogen exchange and platelet function. J Thromb Thrombolysis 8: 15–24, 1999.[CrossRef][Web of Science][Medline]
248. Rothman SM. The neurotoxicity of excitatory amino acids is produced by passive chloride influx. J Neurosci 5: 1483–1489, 1985.[Abstract]
249. Rothstein EC, Byron KL, Reed RE, Fliegel L, and Lucchesi PA. H₂O₂-induced Ca²⁺ overload in NRVM involves ERK1/2 MAP kinases: role for an NHE-1-dependent pathway. Am J Physiol Heart Circ Physiol 283: H598–H605, 2002.[Abstract/Free Full Text]
250. Rothwell NJ. Inflammation in the central nervous system. Philos Trans R Soc Lond B 358: 1669–1677, 2003.[Abstract/Free Full Text]
251. Roy S, Bayly CI, Gareau Y, Houtzager VM, Kargman S, Keen SL, Rowland K, Seiden IM, Thornberry NA, and Nicholson DW. Maintenance of caspase-3 proenzyme dormancy by an intrinsic "safety catch" regulatory tripeptide. Proc Natl Acad Sci USA 98: 6132–6137, 2001.[Abstract/Free Full Text]
252. Rubin Y and Navon G. Inhibition of sodium influx and improved preservation of rat hearts during hypothermic ischemia by furosemide and bumetanide: a 23Na- and 31P-NMR study. J Mol Cell Cardiol 25: 1403–1411, 1993.[CrossRef][Web of Science][Medline]
253. Ruiz-Meana M, Garcia-Dorado D, Pina P, Inserte J, Agullo L, and Soler-Soler J. Cariporide preserves mitochondrial proton gradient and delays ATP depletion in cardiomyocytes during ischemic conditions. Am J Physiol Heart Circ Physiol 285: H999–H1006, 2003.[Abstract/Free Full Text]
254. Russell JM. Sodium-potassium-chloride cotransport. Physiol Rev 80: 211–276, 2000.[Abstract/Free Full Text]
255. Rutledge EM, Aschner M, and Kimelberg HK. Pharmacological characterization of swelling-induced D-[³H]aspartate release from primary astrocyte cultures. Am J Physiol Cell Physiol 274: C1511–C1520, 1998.[Abstract/Free Full Text]
256. Ruwhof C and van der Laarse A. Mechanical stress-induced cardiac hypertrophy: mechanisms and signal transduction pathways. Cardiovasc Res 47: 23–37, 2000.[Abstract/Free Full Text]
257. Ruzicka M, Yuan B, and Leenen FH. Blockade of AT₁ receptors and Na⁺/H⁺ exchanger and LV dysfunction after myocardial infarction in rats. Am J Physiol Heart Circ Physiol 277: H610–H616, 1999.[Abstract/Free Full Text]
258. Sabri A, Byron KL, Samarel AM, Bell J, and Lucchesi PA. Hydrogen peroxide activates mitogen-activated protein kinases and Na⁺-H⁺ exchange in neonatal rat cardiac myocytes. Circ Res 82: 1053–1062, 1998.[Abstract/Free Full Text]
259. Sarangarajan R, Dhabia N, Soliemani M, Baird N, and Joiner C. NHE-1 is the sodium-hydrogen exchanger isoform present in erythroid cells. Biochim Biophys Acta 1374: 56–62, 1998.[Medline]
260. Sardet C, Fafournoux P, and Pouyssegur J. -Thrombin, epidermal growth factor, and okadaic acid activate the Na⁺/H⁺ exchanger, NHE-1, by phosphorylating a set of common sites. J Biol Chem 266: 19166–19171, 1991.[Abstract/Free Full Text]
261. Schaefer S and Ramasamy R. Short-term inhibition of the Na-H exchanger limits acidosis and reduces ischemic injury in the rat heart. Cardiovasc Res 34: 329–336, 1997.[Abstract/Free Full Text]
262. Schielke GP, Moises HC, and Betz AL. Blood to brain sodium transport and interstitial fluid potassium concentration during early focal ischemia in the rat. J Cereb Blood Flow Metab 11: 466–471, 1991.[Web of Science][Medline]
263. Schneider D, Gerhardt E, Bock J, Muller MM, Wolburg H, Lang F, and Schulz JB. Intracellular acidification by inhibition of the Na⁺/H⁺ exchanger leads to caspase-independent death of cerebellar granule neurons resembling paraptosis. Cell Death Differ 11: 760–770, 2004.[CrossRef][Web of Science][Medline]
264. Scholz W and Albus U. Potential of selective sodium-hydrogen exchange inhibitors in cardiovascular therapy. Cardiovasc Res 29: 184–188, 1995.[CrossRef][Web of Science][Medline]
265. Schomberg SL, Bauer J, Kintner DB, Su G, Flemmer A, Forbush B, and Sun D. Cross talk between the GABA_A receptor and the Na-K-Cl cotransporter is mediated by intracellular Cl-. J Neurophysiol 89: 159–167, 2003.[Abstract/Free Full Text]
266. Schomberg SL, Su G, Haworth RA, and Sun D. Stimulation of Na-K-2Cl cotransporter in neurons by activation of non-NMDA ionotropic receptor and group-I mGluRs. J Neurophysiol 85: 2563–2575, 2001.[Abstract/Free Full Text]
267. Schomig A and Richardt G. Cardiac sympathetic activity in myocardial ischemia: release and effects of noradrenaline. Basic Res Cardiol 85, Suppl 1: 9–30, 1990.[CrossRef][Web of Science][Medline]
268. Seki S, Taniguchi M, Takeda H, Nagai M, Taniguchi I, and Mochizuki S. Inhibition by KB-r7943 of the reverse mode of the Na⁺/Ca²⁺ exchanger reduces Ca²⁺ overload in ischemic-reperfused rat hearts. Circ J 66: 390–396, 2002.[CrossRef][Web of Science][Medline]
269. Semplicini A, Spalvins A, and Canessa M. Kinetics and stoichiometry of the human red cell Na⁺/H⁺ exchanger. J Membr Biol 107: 219–228, 1989.[CrossRef][Web of Science][Medline]
270. Sheldon C and Church J. Reduced contribution from Na⁺/H⁺ exchange to acid extrusion during anoxia in adult rat hippocampal CA1 neurons. J Neurochem 88: 594–603, 2004.[CrossRef][Web of Science][Medline]
271. Shen AC and Jennings RB. Myocardial calcium and magnesium in acute ischemic injury. Am J Pathol 67: 417–440, 1972.[Web of Science][Medline]
272. Shrode LD, Gan BS, D'Souza SJ, Orlowski J, and Grinstein S. Topological analysis of NHE1, the ubiquitous Na⁺/H⁺ exchanger using chymotryptic cleavage. Am J Physiol Cell Physiol 275: C431–C439, 1998.[Abstract/Free Full Text]
273. Shrode LD, Klein JD, O'Neill WC, and Putnam RW. Shrinkage-induced activation of Na⁺/H⁺ exchange in primary rat astrocytes: role of myosin light-chain kinase. Am J Physiol Cell Physiol 269: C257–C266, 1995.[Abstract/Free Full Text]
274. Shrode LD, Tapper H, and Grinstein S. Role of intracellular pH in proliferation, transformation, and apoptosis. J Bioenerg Biomembr 29: 393–399, 1997.[CrossRef][Web of Science][Medline]
275. Shuaib A, Xu WC, Yang T, and Noor R. Effects of nonpeptide V₁ vasopressin receptor antagonist SR-49059 on infarction volume and recovery of function in a focal embolic stroke model. Stroke 33: 3033–3037, 2002.[Abstract/Free Full Text]
276. Siegl PK, Cragoe EJ Jr, Trumble MJ, and Kaczorowski GJ. Inhibition of Na⁺/Ca²⁺ exchange in membrane vesicle and papillary muscle preparations from guinea pig heart by analogs of amiloride. Proc Natl Acad Sci USA 81: 3238–3242, 1984.[Abstract/Free Full Text]
277. Siesjo BK. Pathophysiology and treatment of focal cerebral ischemia. Part I: pathophysiology. J Neurosurg 77: 169–184, 1992.[Web of Science][Medline]
278. Silver IA, Deas J, and Erecinska M. Ion homeostasis in brain cells: differences in intracellular ion responses to energy limitation between cultured neurons and glial cells. Neuroscience 78: 589–601, 1997.[CrossRef][Web of Science][Medline]
279. Silver IA and Erecinska M. Intracellular and extracellular changes of [Ca²⁺] in hypoxia and ischemia in rat brain in vivo. J Gen Physiol 95: 837–866, 1990.[Abstract/Free Full Text]
280. Silver RB, Mackins CJ, Smith NC, Koritchneva IL, Lefkowitz K, Lovenberg TW, and Levi R. Coupling of histamine H3 receptors to neuronal Na⁺/H⁺ exchange: a novel protective mechanism in myocardial ischemia. Proc Natl Acad Sci USA 98: 2855–2859, 2001.[Abstract/Free Full Text]
281. Sipos H, Torocsik B, Tretter L, and Adam-Vizi V. Impaired regulation of pH homeostasis by oxidative stress in rat brain capillary endothelial cells. Cell Mol Neurobiol 25: 141–151, 2005.[CrossRef][Web of Science][Medline]
282. Smith GA, Brett CL, and Church J. Effects of noradrenaline on intracellular pH in acutely dissociated adult rat hippocampal CA1 neurones. J Physiol 512: 487–505, 1998.[Abstract/Free Full Text]
283. Somjen GG. Ion regulation in the brain: implications for pathophysiology. Neuroscientist 8: 254–267, 2002.[Abstract/Free Full Text]
284. Steenbergen C, Fralix TA, and Murphy E. Role of increased cytosolic free calcium concentration in myocardial ischemic injury. Basic Res Cardiol 88: 456–470, 1993.[CrossRef][Web of Science][Medline]
285. Steward LC, Vander Elst L, and Ingwall JS. Inhibition of Na⁺ pump in ischemic guinea pig myocardium. Biophys J 55: 510A, 1989.
286. Stromer H, de Groot MC, Horn M, Faul C, Leupold A, Morgan JP, Scholz W, and Neubauer S. Na⁺/H⁺ exchange inhibition with HOE642 improves postischemic recovery due to attenuation of Ca²⁺ overload and prolonged acidosis on reperfusion. Circulation 101: 2749–2755, 2000.[Abstract/Free Full Text]
287. Stuart J and Nash GB. Red cell deformability and haematological disorders. Blood Rev 4: 141–147, 1990.[CrossRef][Web of Science][Medline]
288. Stys PK, Waxman SG, and Ransom BR. Ionic mechanisms of anoxic injury in mammalian CNS white matter: role of Na⁺ channels and Na⁺-Ca²⁺ exchanger. J Neurosci 12: 430–439, 1992.[Abstract]
289. Su G, Kintner DB, Flagella M, Shull GE, and Sun D. Astrocytes from Na⁺-K⁺-2Cl^– cotransporter-null mice exhibit absence of swelling and decrease in EAA release. Am J Physiol Cell Physiol 282: C1147–C1160, 2002.[Abstract/Free Full Text]
290. Su G, Kintner DB, and Sun D. Contribution of Na⁺-K⁺-2Cl^– cotransporter to high-[K⁺]_o- induced swelling and EAA release in astrocytes. Am J Physiol Cell Physiol 282: C1136–C1146, 2002.[Abstract/Free Full Text]
291. Sugiyama S, Satoh H, Nomura N, Terada H, Watanabe H, and Hayashi H. The importance of glycolytically-derived ATP for the Na⁺/H⁺ exchange activity in guinea pig ventricular myocytes. Mol Cell Biochem 217: 153–161, 2001.[CrossRef][Web of Science][Medline]
292. Sun D, Lytle C, and O'Donnell ME. Astroglial cell-induced expression of Na-K-Cl cotransporter in brain microvascular endothelial cells. Am J Physiol Cell Physiol 269: C1506–C1512, 1995.[Abstract/Free Full Text]
293. Sun D, Lytle C, and O'Donnell ME. IL-6 secreted by astroglial cells regulates Na-K-Cl cotransport in brain microvessel endothelial cells. Am J Physiol Cell Physiol 272: C1829–C1835, 1997.[Abstract/Free Full Text]
294. Sun HY, Wang NP, Halkos ME, Kerendi F, Kin H, Wang RX, Guyton RA, and Zhao ZQ. Involvement of Na⁺/H⁺ exchanger in hypoxia/re-oxygenation-induced neonatal rat cardiomyocyte apoptosis. Eur J Pharmacol 486: 121–131, 2004.[CrossRef][Web of Science][Medline]
295. Sung KW, Kirby M, McDonald MP, Lovinger DM, and Delpire E. Abnormal GABAA receptor-mediated currents in dorsal root ganglion neurons isolated from Na-K-2Cl cotransporter null mice. J Neurosci 20: 7531–7538, 2000.[Abstract/Free Full Text]
296. Suvatne J, Barakat AI, O'Donnell ME. Flow-induced expression of endothelial Na-K-Cl cotransport: dependence on K⁺ and Cl^– channels. Am J Physiol Cell Physiol 280: C216–C227, 2001.[Abstract/Free Full Text]
297. Takasu A, Matsushima S, Takino M, and Okada Y. Effect of an endothelin-1 antagonist, BQ-485, on cerebral oxygen metabolism after complete global cerebral ischemia in dogs. Resuscitation 34: 65–69, 1997.[CrossRef][Web of Science][Medline]
298. Takayama E, Guo LL, Digerness SB, and Pike MM. Early reperfusion levels of Na⁺ and Ca²⁺ are strongly associated with postischemic functional recovery but are disassociated from K_ATP channel-induced cardioprotection. J Mol Cell Cardiol 37: 483–496, 2004.[CrossRef][Web of Science][Medline]
299. Takewaki S, Kuro-o M, Hiroi Y, Yamazaki T, Noguchi T, Miyagishi A, Nakahara K, Aikawa M, Manabe I, and Yazaki Y. Activation of Na⁺/H⁺ antiporter (NHE-1) gene expression during growth, hypertrophy and proliferation of the rabbit cardiovascular system. J Mol Cell Cardiol 27: 729–742, 1995.[Web of Science][Medline]
300. Teshima Y, Akao M, Jones SP, and Marban E. Cariporide (HOE642), a selective Na⁺-H⁺ exchange inhibitor, inhibits the mitochondrial death pathway. Circulation 108: 2275–2281, 2003.[Abstract/Free Full Text]
301. Thangaraju M, Sharma K, Liu D, Shen SH, and Srikant CB. Interdependent regulation of intracellular acidification and SHP-1 in apoptosis. Cancer Res 59: 1649–1654, 1999.[Abstract/Free Full Text]
302. Thomas R, Salter MG, Wilke S, Husen A, Allcock N, Nivison M, Nnoli AN, and Fern R. Acute ischemic injury of astrocytes is mediated by Na-K-Cl cotransport and not Ca²⁺ influx at a key point in white matter development. J Neuropathol Exp Neurol 63: 856–871, 2004.[Web of Science][Medline]
303. Tiffert T, Etzion Z, Bookchin RM, and Lew VL. Effects of deoxygenation on active and passive Ca²⁺ transport and cytoplasmic Ca²⁺ buffering in normal human red cells. J Physiol 464: 529–544, 1993.[Abstract/Free Full Text]
304. Tozzi-Ciancarelli MG, Di Massimo C, Mascioli A, Tozzi E, Gallo P, Fedele F, and Dagianti A. Rheological features of erythrocytes in acute myocardial infarction. Cardioscience 4: 231–234, 1993.[Web of Science][Medline]
305. Trafton J, Tombaugh G, Yang S, and Sapolsky R. Salutary and deleterious effects of acidity on an indirect measure of metabolic rate and ATP concentrations in CNS cultures. Brain Res 731: 122–131, 1996.[CrossRef][Web of Science][Medline]
306. Tran L, Anderson SE, and O'Donnell ME. Reduction of cerebral edema by bumetanide administered after initiation of permanent middle cerebral artery occlusion (Abstract). FASEB J 19, A808, 2005.
307. Tran LQ, Anderson SE, and O'Donnell ME. HOE-642 and bumetanide reduce edema formation and infarct following permanent rat middle cerebral artery occlusion (Abstract). FASEB J 18: A1069, 2004.
308. Trapp S, Luckermann M, Brooks PA, and Ballanyi K. Acidosis of rat dorsal vagal neurons in situ during spontaneous and evoked activity. J Physiol 496: 695–710, 1996.[Abstract/Free Full Text]
309. Tsai KL, Wang SM, Chen CC, Fong TH, and Wu ML. Mechanism of oxidative stress-induced intracellular acidosis in rat cerebellar astrocytes and C6 glioma cells. J Physiol 502: 161–174, 1997.
310. Tse CM, Levine SA, Yun CH, Montrose MH, Little PJ, Pouyssegur J, and Donowitz M. Cloning and expression of a rabbit cDNA encoding a serum-activated ethylisopropylamiloride-resistant epithelial Na⁺/H⁺ exchanger isoform (NHE-2). J Biol Chem 268: 11917–11924, 1993.[Abstract/Free Full Text]
311. Tuominen A, Rissanen E, Bogdanova A, and Nikinmaa M. Intracellular pH regulation in rainbow trout (Oncorhynchus mykiss) hepatocytes: the activity of sodium/proton exchange is oxygen-dependent. J Comp Physiol [B] 173: 301–308, 2003.[CrossRef][Medline]
312. van Emous JG, Nederhoff MG, Ruigrok TJ, and van Echteld CJ. The role of the Na⁺ channel in the accumulation of intracellular Na⁺ during myocardial ischemia: consequences for post-ischemic recovery. J Mol Cell Cardiol 29: 85–96, 1997.[CrossRef][Web of Science][Medline]
313. Vaughan-Jones RD and Wu ML. Extracellular H⁺ inactivation of Na⁺/H⁺ exchange in the sheep cardiac Purkinje fibre. J Physiol 428: 441–466, 1990.[Abstract/Free Full Text]
314. Vibat CR, Holland MJ, Kang JJ, Putney LK, and O'Donnell ME. Quantitation of Na⁺-K⁺-2Cl^– cotransport splice variants in human tissues using kinetic polymerase chain reaction. Anal Biochem 298: 218–230, 2001.[CrossRef][Web of Science][Medline]
315. Vigne P, Desmarets J, Guedin D, and Frelin C. Properties of an endothelin-3-sensitive Eta-like endothelin receptor in brain capillary endothelial cells. Biochem Biophys Res Commun 220: 839–842, 1996.[CrossRef][Web of Science][Medline]
316. von Lewinski D, Stumme B, Maier LS, Luers C, Bers DM, and Pieske B. Stretch-dependent slow force response in isolated rabbit myocardium is Na⁺ dependent. Cardiovasc Res 57: 1052–1061, 2003.[Abstract/Free Full Text]
317. Vornov JJ, Thomas AG, and Jo D. Protective effects of extracellular acidosis and blockade of sodium/hydrogen ion exchange during recovery from metabolic inhibition in neuronal tissue culture. J Neurochem 67: 2379–2389, 1996.[Web of Science][Medline]
318. Wakabayashi S, Bertrand B, Ikeda T, Pouyssegur J, and Shigekawa M. Mutation of calmodulin-binding site renders the Na⁺/H⁺ exchanger (NHE1) highly H⁺-sensitive and Ca²⁺ regulation-defective. J Biol Chem 269: 13710–13715, 1994.[Abstract/Free Full Text]
319. Wakabayashi S, Fafournoux P, Sardet C, and Pouyssegur J. The Na⁺/H⁺ antiporter cytoplasmic domain mediates growth factor signals and controls "H⁺-sensing". Proc Natl Acad Sci USA 89: 2424–2428, 1992.[Abstract/Free Full Text]
320. Wakabayashi S, Pang T, Su X, and Shigekawa M. A novel topology model of the human Na⁺/H⁺ exchanger isoform 1. J Biol Chem 275: 7942–7949, 2000.[Abstract/Free Full Text]
321. Wallert MA and Frohlich O. ₁-Adrenergic stimulation of Na-H exchange in cardiac myocytes. Am J Physiol Cell Physiol 263: C1096–C1102, 1992.[Abstract/Free Full Text]
322. Wang GJ, Randall RD, and Thayer SA. Glutamate-induced intracellular acidification of cultured hippocampal neurons demonstrates altered energy metabolism resulting from Ca²⁺ loads. J Neurophysiol 72: 2563–2569, 1994.[Abstract/Free Full Text]
323. Wang H, Yan Y, Kintner DB, Lytle C, and Sun D. GABA-mediated trophic effect on oligodendrocytes requires Na-K-2Cl cotransport activity. J Neurophysiol 90: 1257–1265, 2003.[Abstract/Free Full Text]
324. Wang Y, Meyer JW, Ashraf M, and Shull GE. Mice with a null mutation in the NHE1 Na⁺/H⁺ exchanger are resistant to cardiac ischemia-reperfusion injury. Circ Res 93: 776–782, 2003.[Abstract/Free Full Text]
325. Whalley DW, Hemsworth PD, Rasmussen HH. Sodium-hydrogen exchange in guinea-pig ventricular muscle during exposure to hyperosmolar solutions. J Physiol 444: 193–212, 1991.[Abstract/Free Full Text]
326. Williams KA. Three-dimensional structure of the ion-coupled transport protein NhaA. Nature 403: 112–115, 2000.[CrossRef][Medline]
327. Wright AR and Rees SA. Cardiac cell volume: crystal clear or murky waters? A comparison with other cell types. Pharmacol Ther 80: 89–121, 1998.[CrossRef][Web of Science][Medline]
328. Wu KL, Khan S, Lakhe-Reddy S, Jarad G, Mukherjee A, Obejero-Paz CA, Konieczkowski M, Sedor JR, and Schelling JR. The NHE1 Na⁺/H⁺ exchanger recruits ezrin/radixin/moesin proteins to regulate Akt-dependent cell survival. J Biol Chem 279: 26280–26286, 2004.[Abstract/Free Full Text]
329. Wu ML and Vaughan-Jones RD. Effect of metabolic inhibitors and second messengers upon Na⁺/H⁺ exchange in the sheep cardiac Purkinje fibre. J Physiol 478: 301–313, 1994.[Abstract/Free Full Text]
330. Wu Q, Delpire E, Hebert SC, and Strange K. Functional demonstration of Na⁺-K⁺-2Cl^– cotransporter activity in isolated, polarized choroid plexus cells. Am J Physiol Cell Physiol 275: C1565–C1572, 1998.[Abstract/Free Full Text]
331. Xiao XH and Allen DG. Role of Na⁺/H⁺ exchanger during ischemia and preconditioning in the isolated rat heart. Circ Res 85: 723–730, 1999.[Abstract/Free Full Text]
332. Xiao XH and Allen DG. The role of endogenous angiotensin II in ischaemia, reperfusion and preconditioning of the isolated rat heart. Pflügers Arch 445: 643–650, 2003.[Web of Science][Medline]
333. Yamazaki T, Komuro I, Kudoh S, Zou Y, Nagai R, Aikawa R, Uozumi H, and Yazaki Y. Role of ion channels and exchangers in mechanical stretch-induced cardiomyocyte hypertrophy. Circ Res 82: 430–437, 1998.[Abstract/Free Full Text]
334. Yan Y, Dempsey RJ, Flemmer A, Forbush B, and Sun D. Inhibition of Na⁺-K⁺-2Cl^– cotransporter during focal cerebral ischemia decreases edema and neuronal damage. Brain Res 961: 22–31, 2003.[CrossRef][Web of Science][Medline]
335. Yan Y, Dempsey RJ, and Sun D. Expression of Na⁺-K⁺-2Cl^– cotransporter in rat brain during development and its localization in mature astrocytes. Brain Res 911: 43–55, 2001.[CrossRef][Web of Science][Medline]
336. Yan Y, Dempsey RJ, and Sun D. Na⁺-K⁺-Cl^– cotransporter in rat focal cerebral ischemia. J Cereb Blood Flow Metab 21: 711–721, 2001.[CrossRef][Web of Science][Medline]
337. Yao H, Gu XQ, Douglas RM, and Haddad GG. Role of Na⁺/H⁺ exchanger during O₂ deprivation in mouse CA1 neurons. Am J Physiol Cell Physiol 281: C1205–C1210, 2001.[Abstract/Free Full Text]
338. Yao H and Haddad GG. Calcium and pH homeostasis in neurons during hypoxia and ischemia. Cell Calcium 36: 247–255, 2004.[CrossRef][Web of Science][Medline]
339. Yao H, Ma E, Gu XQ, and Haddad GG. Intracellular pH regulation of CA1 neurons in Na⁺/H⁺ isoform 1 mutant mice. J Clin Invest 104: 637–645, 1999.[Web of Science][Medline]
340. Yasutake M and Avkiran M. Exacerbation of reperfusion arrhythmias by ₁ adrenergic stimulation: a potential role for receptor mediated activation of sarcolemmal sodium-hydrogen exchange. Cardiovasc Res 29: 222–230, 1995.[CrossRef][Web of Science][Medline]
341. Yerby TR, Vibat CR, Sun D, Payne JA, and O'Donnell ME. Molecular characterization of the Na-K-Cl cotransporter of bovine aortic endothelial cells. Am J Physiol Cell Physiol 273: C188–C197, 1997.[Abstract/Free Full Text]
342. Yu SP, Canzoniero LM, and Choi DW. Ion homeostasis and apoptosis. Curr Opin Cell Biol 13: 405–411, 2001.[CrossRef][Web of Science][Medline]
343. Zawadzka M and Kaminska B. A novel mechanism of FK506-mediated neuroprotection: downregulation of cytokine expression in glial cells. Glia 49: 36–51, 2005.[CrossRef][Web of Science][Medline]
344. Zhan RZ, Fujiwara N, Tanaka E, and Shimoji K. Intracellular acidification induced by membrane depolarization in rat hippocampal slices: roles of intracellular Ca²⁺ and glycolysis. Brain Res 780: 86–94, 1998.[CrossRef][Web of Science][Medline]
345. Zhao ZQ and Vinten-Johansen J. Myocardial apoptosis and ischemic preconditioning. Cardiovasc Res 55: 438–455, 2002.[Abstract/Free Full Text]

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