Barium inhibition of sodium ion transport in toad bladder.

The effect of Ba2+ on Na+ transport and electrical characteristics of toad bladder was determined from change produced in short circuit current (Isc), epithelial, apical and basal-lateral potentials (psit, psia, psib), epithelial and membrane resistances (Rt, Ra, Rb) and shunt resistance (Rs). Mucosal Ba2+ had no effect. Serosal Ba2+ reduced Isc, psit, psia, and psib, but had no effect on Rt, Ra, Rb and Rs. Minimal effective Ba2+ concentration was 5-10(-5) M. The phenomenon was reversed by Ba2+ removal, but not by 86 mM serosal K+. Ba2+ inhibition of Isc did not impair the response to vasopressin which was quantitatively the same as controls. Psia with Ba2+ equalled psib. After Ba2+ inhibition, ouabain produced no further decrease in psit and Isc. Ba2+ exposure after ouabain did not decrease psit and Isc. The results suggest that Ba2+ inhibits the basal-lateral electrogenic Na+ pump.