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

Summary

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.