Role of Cl channels in Cl-dependent Na/H exchange.

A novel Na/H exchange activity that requires Cl was recently identified in the apical membrane of crypt cells of the rat distal colon. This study explores the nature of the coupling of Cl and Na/H exchange. A concentration of 100 μM 5-nitro-2-(3-phenylpropylamino)benzoic acid, a Cl channel blocker, inhibited the Cl dependence of both proton gradient-driven22Na uptake from crypt cell apical membrane vesicles and Na-dependent intracellular pH recovery from an acid load during microperfusion of the crypt lumen. Cl-dependent proton gradient-driven 22Na uptake was inhibited by 94% by 500 μM DIDS but only by 1% by 10 μM DIDS, an anion exchange inhibitor at low concentrations but a Cl channel blocker at high concentrations. In addition, a polyclonal antibody to the cystic fibrosis transmembrane conductance regulator (CFTR) inhibited Cl-dependent proton gradient-driven22Na uptake by 38%. These results indicate that the Cl dependence of Na/H exchange in the colonic crypt apical membrane involves a Cl channel and not a Cl/anion exchange and permit the speculation that this Cl channel activity represents both CFTR and the outward rectifying Cl conductance.