Basolateral membrane potassium conductance is independent of sodium pump activity and membrane voltage in canine tracheal epithelium.

Abstract

When secretagogues stimulate Cl secretion in canine tracheal epithelium, apical membrane Cl conductance (GCla) increases, and then basolateral membrane K conductance (GKb) increases. Conversely, inhibition of GCla results in a secondary decrease in GKb. The coordination of the two membrane conductances and regulation of GKb is critical for maintaining constant intracellular ion concentrations and transepithelial Cl secretion. The purpose of this study was to test two hypotheses about the regulation of GKb. First, we asked whether GKb is directly linked to the activity of the Na,K-ATPase. We found that pump activity could be dissociated from K conductance. Inhibition of the Na pump with ouabain, in nonsecreting tissues led to an increase in Gb. Elevation of the bathing solution K concentration produced a similar effect. Addition of ouabain to secreting tissues did not appear to alter Gb. These results indicate that GKb does not directly parallel Na pump activity. Second, we asked whether changes in GKb are voltage dependent. We prevented secretagogue-induced depolarization of the electrical potential difference across the basolateral membrane psi b by clamping psi b at its resting value during stimulation of Cl secretion with epinephrine. Despite maintaining psi b constant, the typical changes in transepithelial resistance and the ratio of membrane resistances persisted. This observation indicates that depolarization is not required for the secretagogue-induced increase in GKb. In addition we examined the effect of depolarizing and hyperpolarizing psi b by passing transepithelial current in secreting and nonsecreting epithelia.(ABSTRACT TRUNCATED AT 250 WORDS)