Basolateral K⁺ conductances in surface epithelium of Necturus antrum: Effects of Ca²⁺ and divalent cations

Intracellular microelectrode techniques were used to characterize basolateral membrane K⁺ conductances in isolated Necturus antral mucosa. Exposure of tissues to progressively higher levels of serosal K⁺ (4, 20, 40, or 60 mM) resulted in progressively greater depolarizations of basolateral membrane potentials and decreases in membrane resistance, consistent with the presence of a significant K⁺ conductance. Ba²⁺ (2 mM) partially blocks these conductances. Exposure of tissues to increased levels of serosal Ca²⁺ (from 1.8 to 6.8 mM) elicited significant hyperpolarization of basolateral potentials and decreases in basolateral resistance. These effects are also elicited by Sr²⁺ (5 mM), but not by Mg²⁺ (5 mM). Ba²⁺ (5 mM) elicits complex and time-dependent effects, but transiently elicits an effect similar to high Ca²⁺. Ion substitutions in the serosal perfusate suggest that the Ca²⁺-induced effects are due to enhancement of basolateral K⁺ conductances. Further work is necessary to identify the processes that mediate this increase in basolateral K⁺ conductance and to evaluate the physiological significance of this change in membrane permeability to K⁺.