Active chloride transport in the isolated toad bladder

Abstract

The toad bladder exhibits K-dependent active Na transport. Removal of K from both mucosal (M) and serosal (S) bathing media, or from the serosal medium alone, results in a marked decrease in the transbladder electrical potential difference (PD), followed in all cases by a reversal of polarity. The reversed PD and short-circuit current (scc) stabilize after 60-90 min. and remain stable for 8 hr. or more. The PD varies from -2 to -77 mv, and the scc from -2 to -150 [mu]a. Replacement of K results in reestablishment of PD and scc of normal orientation and magnitude. The reversed PD and scc are obliterated by the addition of 2,4-dinitro-phenol or sodium cyanide. Measurement of bidirectional chloride fluxes in the shortcircuited K-depleted state revealed net M [forward arrow] S chloride transport that was partially inhibited by ouabain. The negative scc is dependent on the mucosal chloride concentration, but independent of mucosal sodium.