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This Article Full Text Full Text (PDF) All Versions of this Article: 293/6/R2382    most recent 00029.2007v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Reichel, V. Articles by Fricker, G. PubMed PubMed Citation Articles by Reichel, V. Articles by Fricker, G.

COMPARATIVE AND EVOLUTIONARY PHYSIOLOGY

Transport of a fluorescent cAMP analog in teleost proximal tubules

¹Institute of Pharmacy and Molecular Biotechnology, University of Heidelberg, Heidelberg, Germany; ²Department of Pharmacology and Toxicology, Nijmegen Centre for Molecular Life Sciences, Radboud University Nijmegen Medical Centre, Nijmegen, The Netherlands; ³Laboratory of Pharmacology and Chemistry, National Institutes of Health/National Institute of Environmental Health Sciences, Research Triangle Park, North Carolina; and ⁴Mount Desert Island Biological Laboratory, Salisbury Cove, Maine

Previous studies have shown that killifish (Fundulus heteroclitus) renal proximal tubules express a luminal membrane transporter that is functionally and immunologically analogous to the mammalian multidrug resistance-associated protein isoform 2 (Mrp2, ABCC2). Here we used confocal microscopy to investigate in killifish tubules the transport of a fluorescent cAMP analog (fluo-cAMP), a putative substrate for Mrp2 and Mrp4 (ABCC4). Steady-state luminal accumulation of fluo-cAMP was concentrative, specific, and metabolism-dependent, but not reduced by high K⁺ medium or ouabain. Transport was not affected by p-aminohippurate (organic anion transporter inhibitor) or p-glycoprotein inhibitor (PSC833), but cell-to-lumen transport was reduced in a concentration-dependent manner by Mrp inhibitor MK571, leukotriene C₄ (LTC₄), azidothymidine (AZT), cAMP, and adefovir; the latter two compounds are Mrp4 substrates. Although MK571 and LTC₄ reduced transport of the Mrp2 substrate fluorescein-methotrexate (FL-MTX), neither cAMP, adefovir, nor AZT affected FL-MTX transport. Fluo-cAMP transport was not reduced when tubules were exposed to endothelin-1, Na nitroprusside (an nitric oxide generator) or phorbol ester (PKC activator), all of which signal substantial reductions in cell-to-lumen FL-MTX transport. Fluo-cAMP transport was reduced by forskolin, and this reduction was blocked by the PKA inhibitor H-89. Finally, in membrane vesicles from Spodoptera frugiperda (Sf9) cells containing human MRP4, ATP-dependent and specific uptake of fluo-cAMP could be demonstrated. Thus, based on inhibitor specificity and regulatory signaling, cell-to-lumen transport of fluo-cAMP in killifish renal tubules is mediated by a transporter distinct from Mrp2, presumably a teleost form of Mrp4.

killifish; multidrug resistance-associated protein 4