Evidence for an anion exchanger in the mouse lacrimal gland acinar cell membrane

Abstract

Anion exchange transport in the mouse lacrimal gland acinar cell membrane was studied by measuring the intracellular H+ (pHi) and Cl- (aCli) activities with double-barreled ion-selective microelectrodes. In a HCO3- -free solution of pH 7.4 (HEPES/Tris buffered), pHi was 7.25 and aCli was 33 mM. By an exposure to a HCO3- (25 mM HCO3-/5% CO2, pH 7.4) solution for 15 min, aCli was decreased to 25 mM, and pHi was transiently decreased to about 7.05 within 1 min, then slowly relaxed to 7.18 in 15 min. Intracellular HCO3- concentration [HCO3-]i, calculated by the Henderson-Hasselbalch's equation, was 11 mM at 1 min after the exposure and then slowly increased to 15 mM. Readmission of the HCO3(-)-free solution reversed the changes in aCli and pHi. The intracellular buffering power was about 40 mM/pH. An addition of DIDS (0.2 mM) significantly inhibited the rates of change in aCli, pHi, and [HCO3-]i caused by admission/withdrawal of the HCO3- solution and decreased the buffer value. Replacement of all Cl- with gluconate in the HCO3- solution increased pHi, and readmission of Cl- decreased pHi. The rates of these changes in pHi were reduced by DIDS by 32-45% but not by amiloride (0.3 mM). In the HCO3- solution, a stimulation of intracellular HCO3- production by exposing the tissue to 25 mM NH4+ increased aCli significantly. While in the HCO3(-)-free solution or in the HCO3- solution containing DIDS, exposure to NH4+ had little effect on aCli.(ABSTRACT TRUNCATED AT 250 WORDS)