The role of intercellular channels in the transepithelial transfer of water and sodium in the frog urinary bladder.

Epithelial cells of frog urinary bladders fixed in different physiological states were examined by electron microscopy. It was shown: (1) that when bladders incubated with a hypotonic mucosal medium are water-permeabilized with oxytoxin, arginine-vasotocin, cyclic 3',5'-AMP and theophylline, this leads to a cellular swelling and the opening of intercellular channels; (2) that these effects are not observed when the transepithelial net water flow is suppressed by abolishing the external osmotic driving force; and (3) that modifications in the rate of active sodium transport do not change the morphological appearance of intercellular channels.These results are expecially discussed with respect to the localization to the intracellular site of the final effect of antidiuretic hormone on water permeability, and to the role of intercellular channels in the transepithelial transfer of water and sodium.