Na+‐H+ exchange in sheep parotid endpieces

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Abstract
We have used microspectrofluorimetry with the pH-sensitive dye, BCECF, to examine the control of intracellular pH in the secretory endpieces of the sheep parotid gland. Unstimulated endpieces in HCO3 −-free media have a cytosolic pH of 7.5 ± 0.03 (n = 69) which is maintained by a Na+-dependent proton extrusion process that can be partially supported by Li+ but not by Cs+, and is not affected by changes in extracellular Cl−, HCO3 − or K+. It is not blocked by SITS or DIDS, which inhibit Na+-(nHCO3 − co-transport and Cl−1-HCO3 − exchange, nor is it sensitive to the amiloride analogs, MIA and EIPA, which inhibit Na+-H+ exchangers, although very high concentrations of amiloride itself (1 mmol/l) have a (probably non-specific) inhibitory effect. It seems likely that sheep parotid secretory endpieces do contain a Na+-H+ exchanger that drives secretion of a HCO3 −-rich juice, and that its insensitivity to amiloride and its analogs explains why these drugs do not block fluid secretion by the intact sheep parotid gland.