Bioelectric Properties and Ionic Content in Toad Bladder

The toad bladder, like the kidney tubule, is capable of reabsorbing sodium actively, that is against the electrochemical gradient, and chloride and water passively. The bladder is composed of (a) an epithelial cell layer believed to be the site of the active transport process; (b) a subepithelial layer made up of connective tissue fibers and cells, blood vesels, and bundles of smooth muscle fibers; (c) the serosa, which consists of a simple layer of cells (1). The toad bladder is capable of generating a potential difference of some 10-120 my between its serosal and mucosal surfaces, the serosa being positive with respect to the mucosa. The electrical activity of the bladder can be ultimately accounted for by the active transport of sodium from the mucosal to the serosal side of the organ. When both surfaces of the bladder are exposed to physiological solutions of identical composition and the spontaneous membrane potential is abolished by an imposed external potential difference, the current flowing through the external cricuit is equivalent to the net transport of sodium. This is the short circuit current (2).