A NOVEL-APPROACH ALLOWS IDENTIFICATION OF K-CHANNELS IN THE LATERAL MEMBRANE OF RAT CCD

We have developed a novel approach to study K channels in the lateral membrane of principal cells (PC) in rat cortical collecting ducts (CCD ). The technique consists of 1) exposing the CCD apical membrane, 2) r emoving the intercalated cells adjoining a PC by gentle suction throug h a pipette, and 3) applying patch-clamp technique to the lateral memb rane of PC. Functional viability of the PC was confirmed by three inde xes: 1) maintenance of physiological cell membrane potentials (-85 +/- 3 mV); 2) depolarization of the cell membrane potential with 1 mM Ba2 +; and 3) hyperpolarization of the cell potential with 0.1 mM amilorid e. Two types of K channels were identified: a low-conductance K channe l and an intermediate-conductance K channel. In cell-attached patches the slope conductance of the low-conductance K channel was 27 pS and t hat of the intermediate-conductance K channel was 45 pS. The open prob ability (P-o) of the 27-pS K channel was 0.81 +/- 0.02 and was not vol tage dependent. In contrast, the P-o of the 45-pS K channelwas 0.23 +/ - 0.01 at the spontaneous cell membrane potential and was increased by hyperpolarization. In addition, decrease of the bath pH from 7.4 to 6 .7 reduced the 27-pS K channel current amplitude in a voltage-dependen t manner, but the P-o was not affected. Finally, two time constants we re required to fit open- and closed-time histograms of both population s of K channels. Application of 1 mM Ba2+ completely blocked these K c hannels. We conclude that two types of K channel are present in the ba solateral membrane of PC.