Intracellular pH regulation in the mouse lacrimal gland acinar cells

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Abstract
Intracellular pH (pH i ) of the acinar cells of the isolated, superfused mouse lacrimal gland has been measured using pH-sensitive microelectrodes. Under nonstimulated condition pH i was 7.25, which was about 0.5 unit higher than the equilibrium pH. Alterations of the external pH by ±0.4 unit shifted pH i only by ±0.08 unit. The intracellular buffering value determined by applications of 25mm NH 4 + and bicarbonate buffer solution gassed with 5% CO2/95% O2 was 26 and 46mm/pH, respectively Stimulation with 1 μm acetylcholine (ACh) caused a transient, small decrease and then a sustained increase in pH i . In the presence of amiloride (0.1mm) or the absence of Na+, application of ACh caused a significant decrease in pH i and removal of amiloride or replacement with Na+-containing saline, respectively, rapidly increased the pH i . Pretreatment with DIDS (0.2mm) did not change the pH i of the nonstimulated conditions; however, it significantly enhanced the increase in pH i induced by ACh. The present results showed that (i) there is an active acid extrusion mechanism that is stimulated by ACh; (ii) stimulation with ACh enhances the rate of acid production in the acinar cells; and (iii) the acid extrusion mechanism is inhibited by amiloride addition to and Na+ removal from the bath solution. We suggest that both Na+/H+ and HCO 3 − /Cl− exchange transport mechanisms are taking roles in the intracellular pH regulation in the lacrimal gland acinar cells.