Anion Channels in the Apical Membrane of Collecting Duct Principal Cells in Culture

Ion channels in the apical cell membrane of monolayers of rabbit renal collecting duct principal cells in primary culture were investigated with the patch-clamp technique. Besides three or more types of cation channels published previously, three types of anion channels were observed. Most frequent was an outwardly rectifying Cl– selective channel with the slope conductance of 30.4 ± 4.8 pS (n = 6) in symmetrical isotonic NaCl solutions at 0 mV holding potential. This channel was only observed in excised patches. Its open probability was independent of the calcium concentration at the cytoplasmic surface of the membrane patch. The channel had complex open/close kinetics and was blocked by 5-nitro-2-(3-phenylpropylamino) benzoic acid from the extracellular surface. Inhibition increased at more cytoplasm-positive membrane potentials. Secondly, a high conductance, poorly selective anion channel was observed. It had a linear current voltage (I/V) relation with a conductance of 267 ± 46 pS (n = 4) and exhibited at least four substates. The open probability of this channel decreased sharply with increasing membrane potentials of either polarity. Thirdly, and least frequently, a bursting Cl– selective channel was observed which displayed a peculiar I/V relation in isotonic NaCl solutions. Near 0 mV it had a slope conductance of ≈ 50 pS which increased to 113 ± 11 pS (n = 4) at potentials exceeding ± 50 mV. Since the peritubular cell membrane of principal cells is Cl– permeable, it is conceivable that one or more of these channels contribute to collecting duct Cl– absorption particularly in situations in which the luminal Cl– concentration and the transepithelial potential difference are high.