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

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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 HCO 3 − -free solution of pH 7.4 (HEPES/Tris buffered), pHi was 7.25 andaCli was 33mm. By an exposure to a HCO 3 − (25mm HCO 3 − /5% CO2, pH 7.4) solution for 15 min,aCli was decreased to 25mm and pHi was transiently decreased to about 7.05 within 1 min, then slowly relaxed to 7.18 in 15 min. Intracellular HCO 3 − concentration [HCO 3 − ]i, calculated by the Henderson-Hasselbalch's equation, was 11mm at 1 min after the exposure and then slowly increased to 15mm. Readmission of the HCO 3 − -free solution reversed the changes inaCli and pHi. The intracellular buffering power was about 40mm/pH. An addition of DIDS (0.2mm) significantly inhibited the rates of change inaCli, pHi, and [HCO 3 − ]i caused by admission/withdrawal of the HCO 3 − , solution and decreased the buffer value. Replacement of all Cl− with gluconate in the HCO 3 − 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 (0.3mm). In the HCO 3 − solution, a stimulation of intracellular HCO 3 − production by exposing the tissue to 25mm NH 4 + increasedaCli significantly. While in the HCO 3 − -free solution or in the HCO 3 − , solution containing DIDS, exposure to NH 4 + had little effect onaCli. All of these findings were consistent with the presence of a reversible, disulfonic stilbene-sensitive Cl−/HCO 3 − exchanger in the basolateral membrane of the acinar cells. The possibility of anion antiport different from one-for-one Cl−/HCO 3 − exchange is discussed.