Chloride channels in the apical membrane of cortical collecting duct cells

Abstract

Ion channels in the apical membrane of cortical collecting duct (CCD) cells in culture were studied by the patch-clamp technique. CCD cells from rabbit kidney were isolated by solid-phase immunoadsorption with a monoclonal antibody. The majority of CCD cells (93%) had phenotypic characteristics similar to intercalated cells (ICC). Although Cl- channels were present in the apical membrane of the ICC cells, they were rarely active in cell-attached patches: however, channels were activated after patch excision. In inside-out patches, the channels exhibited rapid flickering, substrates, and large unitary currents. The single-channel conductance was 303 pS, the Cl--to-Na+ permeability ratio was 10:1 and the Cl--to-HCO3- permeability ratio was 1.5:1. The channel was inhibited by the Cl- channel blockers 4,4''-diisothiocyanostilbene-2,2''-disulfonic acid, diphenylamine carboxylic acid, and 5-nitro-2-(3-phenylpropylamino)-benzoic acid. Although a reduction in the cytoplasmic Ca2+ concentration inhibited channel activity in both inside-out patches and cell-attached patches, alterations of Ca2+ within the physiological range did not change the channel open probability. Finally, changing the cytoplasmic pH (6.5 to 8.0) did not alter the open probability. Thus a large conductance anion channel is present in the apical membrane of CCD cells in culture. This channel may be involved in cell volume regulation or in Cl- and HCO3- secretion.