Effects of 2-deoxy-d-glucose, amiloride, vasopressin, and ouabain on active conductance andE Na in the toad bladder

Abstract

The effects of various agents on active sodium transport were studied in the toad bladder in terms of the equivalent circuit comprising an active conductanceK^a, an electromotive forceE_Na, and a parallel passive conductanceK^p. For agents which affectK^a, but notE_Na orK^p, the inverse slope of the plot of total conductance κ against short-circuit currentI₀ evaluatesE_Na, and the intercept representsK^p. Studies employing 5×10⁻⁷m amiloride to depressK^a indicate a changingE_Na, invalidating the use of the slope technique with this agent. An alternative suitable technique employs 10⁻⁵m amiloride, which reducesI₀ reversibly to near zero without effect onK^p. Despite curvilinearity of the κ-I₀ plot under these conditions,K^p may therefore be estimated fairly precisely from the residual conductance. It then becomes possible to follow the dynamic behavior ofK^a andE_Na (in the absence of 10⁻⁵m amiloride) by frequent measurements of κ andI₀, utilizing the relationshipsK^a=K-K^p, andK_Na=I_O/(K-K^p). 2-deoxy-d-glucose (7.5×10⁻³m) depressedK^a without affectingE_Na. Amiloride (5×10⁻⁷m) depressedK^a and enhancedE_Na. Vasopressin (100 mU/ml) enhancedK^a markedly and depressedE_Na slightly. Ouabain (10⁻⁴m) depressed bothK^a andE_Na. All of the above effects were noted promptly;K^p was unaffected. The “electromotive force of Na transport”E_Na appears not to be a pure energetic parameter, but to reflect kinetic factors as well, in accordance with thermodynamic considerations.