Double-barreled chloride channels of collecting duct basolateral membrane

Microelectrode studies have shown that the basolateral membrane of the principal cells (PC) of the rabbit cortical collecting duct (CCD) contains Cl^--conductive pathways. To determine the properties of single Cl^- channels we prepared the basolateral membrane for patch clamping by incubating the CCD in collagenase and/or tearing the basement membrane with a fine needle. When high concentrations of collagenase were used, only a small nonselective channel was observed. In low concentrations or the absence of collagenase, however, we identified a Cl^- channel (g₄₆) in both cell-attached and excised patches. The Cl^- channel gated rapidly between three equally spaced substates of 0 (S₀), 23 (S₁), and 46 pS (S₂) and slowly between states C (inactive) and S₀. The conductance of each substate was not voltage dependent between pipette potentials from -60 to +60 mV (cell attached). The probability that the channel gated from C to S₀ increased with hyperpolarizing potentials, but the probability that g₄₆ was in substate S₀ increased with depolarizing patch potentials. This channel was similar to that described by Miller for the nonexcitable membrane of the electric organ of Torpedo californica. Because g₄₆ was the most frequently observed basolateral membrane channel and was voltage dependent at physiological potentials, it is probably the channel responsible for the dominant Cl^- conductance of PC.