Na +-H + exchange in sheep parotid endpieces : Apparent insensitivity to amiloride

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 HCO 3 −-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 −, HCO 3 − or K +. It is not blocked by SITS or DIDS, which inhibit Na +-( nHCO 3 − co-transport and Cl −1-HCO 3 − 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 HCO 3 −-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.