Incorporation into a planar lipid bilayer of K channels from the luminal membrane of rabbit proximal tubule

Abstract

The presence of ionic channels at the apical membrane of rabbit proximal tubule cells was investigated by fusion of brush-border membrane vesicles (BBMV) with a planar lipid bilayer (PE/PC, 1:1). The BBMV obtained from native membranes showed poor fusogenic properties. The probability of vesicles fusion with a planar bilayer was, however, enhanced by preincubating the BBMV with liposomes made of azolectin. We report here the presence in BBMV preparations of two K +-selective channels of 65 pS and 40 pS, respectively, in asymmetrical 200/ /50 mM KCl solutions. The channel of 65 pS appeared highly selective to K + over Na + and Cl − ions, while the 40 pS channel discriminated poorly between K + and Na + with a permeability ratio P K/ P Na = 4. The open probability P 0 of both channels was found to be voltage-independent with the potential range −60 mV to +60 mV. These K + channels may be related to channels identified using other methods.