Effects of changes in the composition of the mucosal solution on the electrical properties of the toad urinary bladder epithelium.

By the use of microelectrode techniques, the potential profile and the electrical resistances of the cellular and shunt pathways across the toad urinary bladder epithelium were measured under control conditions and after exposing the mucosal side to solutions of low and high NaCl concentrations and osmolalities. The resistance of the shunt pathway increases at low NaCl concentration (even if the osmolality is kept constant), and decreases at high NaCl concentration (by a nonspecific osmotic mechanism). The inverse relationship between mucosal NaCl concentration and shunt resistance suggests a regulatory mechanism of net sodium transport by reduction of the passive blood-to-urine sodium flux at low urinary sodium concentrations. In addition, the transepithelial potential and the potentials at both cell borders fall in both low and high mucosal NaCl, and the magnitude of these changes is such that they cannot be explained by changes in the shunt pathway alone.