INCORPORATION INTO A PLANAR LIPID BILAYER OF K-CHANNELS FROM THE LUMINAL MEMBRANE OF RABBIT PROXIMAL TUBULE

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(o) of both channels was found to be voltage-independent within the potential range -60 mV to +60 mV. These K+ channels may be related to channels identified using other methods.