Inhibition of basolateral potassium conductance by taurine in the proximal convoluted tubule

The effect of taurine on the electrophysiological properties of the basolateral membrane of the rabbit proximal convoluted tubule was examined. Short-duration isosmotic pulses of 40 mM taurine in the bath solution induced basolateral membrane depolarizations (Delta V-bl) of 6.44 +/- 0.5 mV, which were reduced by 58% in absence of Na+. In presence of barium and quinine, Delta V-bl values were reduced by 55% in Na+-containing bath solutions and were completely abolished in Na+-free solutions. Continuous addition of taurine into the bath solutions or a period of 5 min induced 1) a decrease in the partial conductance of the basolateral membrane to K+ (t(K)) from 0.39 to 0.23; 2) an increase in the partial conductance to Cl- (t(Cl)) from 0.055 to 0.172; 3) a rapid and transient increase of the partial conductance mediated by the Na-HCO3 cotransporter (t(NaHCO3)) from 0.37 to 0.52, followed by a progressive decrease to 0.29 and 4) a depolarization of the basolateral membrane of 16 mV. The absolute membrane conductance mediated by the Na-HCO3 cotransporter was not initially affected by taurine. whereas that to K (G(K)) initially decreased by a maximal factor of 2 after 1 min, followed by a partial recovery after 5 min. and that to Cl (G(Cl)) increased by a factor of 4. Addition of taurine after a hypotonicity-induced cell swelling produced an inhibition of GK comparable to the one observed under isotonic conditions. These results demonstrate the presence of an electrogenic Na-dependent transport of taurine and indicate that taurine inhibits G(K).