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WATER AND ELECTROLYTE HOMEOSTASIS

Functional and molecular characterization of the fluid secretion mechanism in human parotid acinar cells

¹The Center for Oral Biology in the Aab Institute of Biomedical Sciences and the ²Department of Pharmacology and Physiology, University of Rochester School of Medicine and Dentistry, Rochester, New York; and ³Facultad de Medicina and ⁴Instituto de Fisica, Universidad Autonoma de San Luis Potosi, San Luis Potosi, Mexico

Submitted 20 August 2006 ; accepted in final form 5 March 2007

The strategies available for treating salivary gland hypofunction are limited because relatively little is known about the secretion process in humans. An initial microarray screen detected ion transport proteins generally accepted to be critically involved in salivation. We tested for the activity of some of these proteins, as well as for specific cell properties required to support fluid secretion. The resting membrane potential of human acinar cells was near –51 mV, while the intracellular [Cl^–] was 62 mM, about fourfold higher than expected if Cl ions were passively distributed. Active Cl^– uptake mechanisms included a bumetanide-sensitive Na⁺-K⁺-2Cl^– cotransporter and paired DIDS-sensitive Cl^–/HCO₃^– and EIPA-sensitive Na⁺/H⁺ exchangers that correlated with expression of NKCC1, AE2, and NHE1 transcripts, respectively. Intracellular Ca²⁺ stimulated a niflumic acid-sensitive Cl^– current with properties similar to the Ca²⁺-gated Cl channel BEST2. In addition, intracellular Ca²⁺ stimulated a paxilline-sensitive and voltage-dependent, large-conductance K channel and a clotrimazole-sensitive, intermediate-conductance K channel, consistent with the detection of transcripts for KCNMA1 and KCNN4, respectively. Our results demonstrate that the ion transport mechanisms in human parotid glands are equivalent to those in the mouse, confirming that animal models provide valuable systems for testing therapies to prevent salivary gland dysfunction.

salivary glands; secretion; fluid; channels; exchangers; cotransporters

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