Mechanism of active K⁺ secretion by flounder urinary bladder

We investigated the mechanism of active K⁺ transport by the urinary bladder of the winter flounder by measuring transepithelial properties in Ussing Chambers and by determining the cellular electrical potential profile using conventional microelectrodes. In the absence of transmural electrochemical potential gradients isolated bladders can exhibit a serosa-to-mucosa short circuit which is due entirely to net K⁺ secretion. The properties of transcellular K⁺ movement can be adequately described by a model which provides for active K⁺ uptake across the basolateral membrane via an electrogenic Na/K ATPase and K⁺ exit from the cell across the apical membrane down an electrochemical potential gradient via K⁺ channels which are blocked by mucosal barium. The conductance of the apical membranes of the transporting cells appears to be due almost solely to K⁺ while that of the basolateral membrane may be due largely to Cl^-.