Reconstitution of an inwardly rectifying potassium channel from the basolateral membranes of Necturus enterocytes into planar lipid bilayers.

Basolateral membrane vesicles from Necturus enterocytes, highly (greater than 20-fold) enriched in Na+,K+-ATPase, were reconstituted into planar lipid bilayers. The principal channel activity observed is selective for K+ over Na+ and Cl-. This K+ channel is blocked by Ba2+ and Leiurus quinquestriatus venom but is not affected by Ca2+ over the range of 10(-3) to less than 10(-7) M and is not inhibited by charybdotoxin. L. quinquestriatus venom also markedly reduces the conductance of the basolateral membrane of intact villus cells of Necturus small intestine. The open-time probability (Po) of the channel displays a voltage-dependence characteristic of an "inward rectifier"; i.e., the channel inactivates when the basolateral membrane is depolarized and Po increases with increasing hyperpolarization of that barrier. Assuming that similar properties prevail under physiological conditions, this characteristic could provide, in part, an explanation for the parallelism between Na+-pump and K+-leak activities of the basolateral membrane observed in this epithelium. Thus, an increase in rheogenic Na+-pump activity at the basolateral membrane would hyperpolarize that barrier and, in turn, increase the open time of this K+ channel.