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

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)