EFFECTS OF 2-DEOXY-D-GLUCOSE, AMILORIDE, VASOPRESSIN, AND OUABAIN ON ACTIVE CONDUCTANCE AND ENA IN TOAD BLADDER

The effects of various agents on active Na transport were studied in the toad bladder in terms of the equivalent circuit comprising an active conductance .kappa.a, an electromotive force ENa, and a parallel passive conductance .kappa.p. For agents which affect .kappa.a, but not ENa or .kappa.p, the inverse slope of the plot of total conductance .kappa. against short-circuit current IO evaluates ENa, and the intercept represents .kappa.p. Studies employing 5 .times. 10-7 M amiloride to depress .kappa.a indicate a changing ENa, invalidating the use of the slope technique with this agent. An alternative suitable technique employs 10-5 M amiloride, which reduces IO reversibly to near zero without effect on .kappa.p. Despite curvilinearity of the .kappa. - IO plot under these conditions .kappa.p may be estimated fairly precisely from the residual conductance. It then becomes possible to follow the dynamic behavior of .kappa.a and ENa (in the absence of 10-5 M amiloride) by frequent measurements of .kappa. and IO, utilizing the relationships .kappa.a = .kappa. - .kappa.p, and ENa = IO/(.kappa. - .kappa.p). 2-Deoxy-D-glucose (7.5 .times. 10-3 M) depressed .kappa.a without affecting ENa. Amiloride (5 .times. 10-7 M) depressed .kappa.a and enhanced ENa. Vasopressin (100 mU/ml) enhanced .kappa.a markedly and depressed ENa slightly. Ouabain (10-4 M) depressed both .kappa.a and ENa. All of the above effects were noted promptly; .kappa.p was unaffected. The electromotive force of Na transport ENa appears not to be a pure energetic parameter, but to reflect kinetic factors as well, in accordance with thermodynamic considerations.