Potassium dependence of Na-Cl cotransport in dog tracheal epithelium

In confluent primary cultures of dog tracheal epithelium, we tested whether Cl entry across the basolateral membrane is by cotransport with K. Two approaches were taken. First, we measured the inhibition of short-circuit current (I(sc)) by the K channel inhibitor, Ba²⁺. Consistent with Na-K-2Cl cotransport, maximal doses of Ba²⁺ inhibited five-sixths of I(sc) in tissues previously stimulated to secrete Cl; only two-thirds of I(sc) should be sensitive to Ba²⁺ if NaCl cotransport is the entry mechanism. Second, we measured basolateral ⁸⁶Rb uptake and demonstrated inhibition by bumetanide, an inhibitor of Na-K-2Cl cotransport in other tissues. The degree of inhibition by bumetanide was consistent with the levels of Cl secretion measured as I(sc). Uptake of ⁸⁶Rb was also reduced by removal of Na or Cl, and under these conditions Rb uptake was not further inhibited by bumetanide. These results suggest that the process responsible for Cl entry across the basolateral membrane of tracheal epithelium during Cl secretion is Na-K-2Cl rather than Na-Cl cotransport.