Summary
When secretagogues stimulate Cl secretion in canine tracheal epithelium, apical membrane Cl conductance (G Cl a ) increases, and then basolateral membrane K conductance (G K b ) increases. Conversely, inhibition ofG Cl a results in a secondary decrease inG K b . The coordination of the two membrane conductances and regulation ofG K b 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 ofG K b . First, we asked whetherG K b 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 inG b . Elevation of the bathing solution K concentration produced a similar effect. Addition of ouabain to secreting tissues did not appear to alterG b . These results indicate thatG K b does not directly parallel Na pump activity. Second, we asked whether changes inG K b are voltage dependent. We prevented secretagogue-induced depolarization of the electrical potential difference across the basolateral membrane Ψ b by clamping Ψ b at its resting value during stimulation of Cl secretion with epinephrine. Despite maintaining Ψ 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 inG K b . In addition we examined the effect of depolarizing and hyperpolarizing Ψ b by passing transepithelial current in secreting and nonsecreting epithelia. Despite depolarizing and hyperpolarizing Ψ b within the physiologic range, we observed no significant changes in transepithelial resistance or the ratio of membrane resistance that would suggest a change inG K b . This observation indicates that changes in Ψ b are not sufficient to alterG K b . Thus,G K b appears to be regulated by factors other than membrane voltage, or direct coupling to the Na pump.
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Welsh, M.J. Basolateral membrane potassium conductance is independent of sodium pump activity and membrane voltage in canine tracheal epithelium. J. Membrain Biol. 84, 25–33 (1985). https://doi.org/10.1007/BF01871645
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DOI: https://doi.org/10.1007/BF01871645