Functional and molecular characterization of luminal and basolateral Cl−/ HCO 3 − exchangers of rat thick limbs

Abstract

Cl−/[Formula: see text]exchange was measured in luminal (LMV) and basolateral (BLMV) membrane vesicles purified from rat medullary thick ascending limb (MTAL). Cl−/[Formula: see text]exchange in BLMV and LMV was inhibited by DIDS, with respective IC50 values of 3.2 ± 0.9 and 15.2 ± 5.2 μM, whereas Cl− conductances were DIDS insensitive. At constant external pH, BLMV36Cl−/[Formula: see text]and36Cl−/Cl−exchanges exhibited a sigmoidal pattern of activation as internal pH (pHi) increased from 6.1 to 8.0, whereas LMV36Cl−/Cl−exchange was unchanged between pHi6.7 and 7.8. The 165-kDa AE2 polypeptide and ∼115-kDa AE1-related polypeptide were present only in BLMV. In contrast, AE1-related polypeptides of ∼90 and 95 kDa were present not only in BLMV but also (in variable abundance) in LMV. We conclude that rat MTAL BLMV and LMV express distinct anion exchange activities and distinct sets of AE polypeptides. AE2 (and perhaps AE1) in BLMV likely contribute to[Formula: see text] absorption. In contrast, LMV exchangers may contribute to NaCl absorption via parallel coupling with the luminal Na+/H+antiporters and/or may provide negative feedback regulation of[Formula: see text] absorption.