Cl^- transport in basolateral renal medullary vesicles: II. Cl^- channels in planar lipid bilayers

The present studies examined some of the properties of Cl^- channels in renal outer medullary membrane vesicles incorporated into planar lipid bilayers. The predominant channel was anion selective having a P_Cl/P_K ratio of 10 and a unit conductance of 93 pS in symmetric 320 mm KCl. In asymmetric KCl solutions, the I-V relations conformed to the Goldman-Hodgkin-Katz equation. Channel activity was voltage-dependent with a gating charge of unity. This voltage dependence of channel activity may account, at least in part, for the striking voltage dependence of the basolateral membrane Cl^- conductance of isolated medullary thick ascending limb segments. The Cl^- channels incorporated into the planar bilayers were asymmetrical: the trans surface was sensitive to changes in ionized Ca²⁺ concentrations and insensitive to reducing KCl concentrations to 10 mm, while the cis side was insensitive to changes in ionized Ca²⁺ concentrations, but was inactivated by reducing KCl concentrations to 50 mm.