Diversity of K+ channels in the basolateral membrane of restingnecturus oxyntic cells

Abstract
Patch-clamp techniques have been applied to characterize the channels in the basolateral membrane of resting (cimetidine-treated, nonacid secreting) oxyntic cells isolated from the gastric mucosa ofNecturus maculosa. In cell-attached patches with pipette solution containing 100mm KCl, four major classes of K+ channels can be distinguished on the basis of their kinetic behavior and conductance: (1) 40% of the patches contained either voltage-independent (a) or hyperpolarization-activated (b), inward-rectifying channels with short mean open times (16 msec fora, and 8 msec forb). Some channels showed subconductance levels. The maximal inward conductanceg max was 31±5 pS (n=13) and the reversal potentialE rev was atV p=−34±6 mV (n=9). (2) 10% of the patches contained depolarization-activated and inward-rectifying channels withg max=40 ±18 pS (n=3) andE rev was atV p=−31±5 mV (n=3). With hyperpolarization, the channels open in bursts with rapid flickerings within bursts. Addition of carbachol (1mm) to the bath solution in cell-attached patches increased the open probabilityP o of these channels. (3) 10% of the patches contained voltage-independent inward-rectifying channels withg max=21±3 pS (n=4) andE rev was atV p=−24±9 mV (n=4). These channels exhibited very high open probability (P o=0.9) and long mean open time (1.6 sec) at the resting potential. (4) 20% of the patches contained voltage-independent channels with limiting inward conductance of 26±2 pS (n=3) andE rev atV p=−33±3 mV (n=3). The channels opened in bursts consisting of sequential activation of multiple channels with very brief mean open times (10 msec). In addition, channels with conductances less than 6 pS were observed in 20% of the patches. In all nine experiments with K+ in the pipette solution replaced by Na+, unitary currents were outward, and inward currents were observed only for large hyperpolarizing potentials. This indicates that the channels are more selective for K+ over Na+ and Cl. A variety of K+ channels contributes to the basolateral K+ conductance of resting oxyntic cells.