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⁺ (pH_i) and Cl⁻ (aCl_i) activities with double-barreled ion-selective microelectrodes. In a HCO ₃ ⁻ -free solution of pH 7.4 (HEPES/Tris buffered), pH_i was 7.25 andaCl_i was 33mm. By an exposure to a HCO ₃ ⁻ (25mm HCO ₃ ⁻ /5% CO₂, pH 7.4) solution for 15 min,aCl_i was decreased to 25mm and pH_i 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 inaCl_i and pH_i. The intracellular buffering power was about 40mm/pH. An addition of DIDS (0.2mm) significantly inhibited the rates of change inaCl_i, pH_i, 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 pH_i, and readmission of Cl⁻ decreased pH_i. The rates of these changes in pH_i 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 ⁺ increasedaCl_i significantly. While in the HCO ₃ ⁻ -free solution or in the HCO ₃ ⁻ , solution containing DIDS, exposure to NH ₄ ⁺ had little effect onaCl_i. 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.