Regulation of basolateral K channels in proximal tubule studied during continuous microperfusion.

Potassium channel activity of the basolateral membrane of the collagenase-treated rabbit proximal convoluted tubule (PCT) was studied during continuous luminal microperfusion. In cell-attached patches (high-K pipette) an inwardly rectifying potassium channel was observed with an inward slope conductance of 60.8 +/- 3.3 pS (n = 12) and outward slope conductance of 17.1 +/- 2.7 pS (n = 6). Stimulation of transcellular sodium transport with luminal glucose and alanine increased channel activity [measured as single-channel open probability (NPo)] from 0.19 +/- 0.11 to 0.44 +/- 0.09 (n = 8). This increase in channel activity was not likely to be mediated by either cell depolarization or cell swelling, because channel activity was voltage insensitive over physiological potentials and because the channel was not activated by stretch. However, channel activity was pH sensitive; reducing luminal pH from 7.4 to 6.5 reduced NPo from 0.63 +/- 0.24 to 0.26 +/- 0.16 (n = 5). Our work demonstrates the feasibility of patch clamping the basolateral membrane of microperfused nephron segments. This has allowed us to follow the activity of this potassium channel during an increase in sodium transport and show that its activity does increase during this maneuver. We conclude that: 1) it is possible to patch clamp the basolateral membrane of microperfused nephron segments, and 2) basolateral membrane of the rabbit PCT contains an inwardly rectifying, pH-sensitive potassium channel. The behavior of this channel on stimulation of transcellular sodium transport could explain the macroscopic increase in basolateral potassium conductance observed under similar conditions.