Intracellular pH during secretion in the perfused rabbit mandibular salivary gland measured by 31P NMR spectroscopy.

Abstract

Intracellular pH (pHi) was measured in the isolated, perfused rabbit mandibular salivary gland by 31P NMR spectroscopy. In the unstimulated gland perfused with HCO3-/CO2-buffered Ringer's solution, pHi was 7.27 +/- 0.01. Continuous stimulation with acetylcholine elicited dose- and time-dependent changes in pHi. 10(-6) mol/l acetylcholine caused a brief intracellular acidosis (-0.19 +/- 0.06 pH units) followed by an increase in pHi to a more alkaline steady-state value (7.33 +/- 0.02). In the absence of perfusate HCO3- or in the presence of 10(-4) mol/l DIDS (4,4'-diisothiocyanatostilbene-2,2'-disulphonic acid), the transient acidosis was abolished and pHi increased rapidly to give a sustained alkalosis (7.49 +/- 0.03 and 7.44 +/- 0.03 respectively). In the presence of 10(-3) mol/l amiloride, the response to acetylcholine was a rapid decrease in pHi to 7.02 +/- 0.02. The data suggest that, during perfusion with HCO3-/CO2- buffered solutions, stimulation with acetylcholine results in a transient loss of HCO3- from the acinar cells (causing a transient acidosis), and, independently, the activation of Na+-H+ exchange (causing a sustained alkalosis). In the unstimulated gland, DIDS and the HCO3- -free perfusate caused decreases in pHi to 7.12 +/- 0.02 and 7.04 +/- 0.01 respectively. In contrast, amiloride had little effect. The relatively high value of pHi maintained by the unstimulated gland is therefore probably not due to Na+-H+ exchange.