Na + ‐H + exchange in sheep parotid endpieces

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 + ‐( n HCO 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.