Effects of Alkali Metal Gations on the Potential across Toad and Bullfrog Urinary Bladder

Isolated urinary bladders of the bullfrog (R. catesbeiana) and the toad (B. marinus) were mounted in an Ussing chamber. Potential differences up to 114 mv were observed in bullfrog bladder when the mucosal surface was bathed in dilute Na₂SO₄ and the serosal surface in sulfate Ringer's. In experiments with bullfrogs, K was used to replace Na in the mucosal solution and Na was used for K in the serosal solutions. The selectivity was judged in terms of the relative effectiveness of the replacement cation in maintaining the bladder potential. In experiments with toads, K and Rb were equally poor replacements for Na at the mucosal border, while Rb was a good replacement for K at the serosal border. Li in the mucosal solution appeared to depress the potential in part irreversibly. At the serosal border, Li was a partially effective substitute for K, more so than was Na. However, both were poor replacements compared to Rb. The mucosal surface of the urinary bladder of both frog and toad appears to be Na-selective and the serosal surface appears to be K-selective, consistent with the Koefoed-Johnsen-Ussing model for frog skin.