Ultrastructural modifications of frog urinary bladder epithelium under the influence of hypertonic media.

The frog urinary bladder undergoes a marked increase in its water permeability when incubated in hypertonic media. Many similarities are found between this effect and the hydrosmotic action of antidiuretic hormone. The ultrastructural modifications of the epithelium observed under the influence of serosal hypertonicity (the intercellular spaces are dilated while the tight junctions remain closed) lead us to assume that the pathways of water movement across the epithelium could be the same in this case and in hydrosmotic response to the hormone. In contrast, when the mucosal medium is made hypertonic, the ultrastructure is differently altered: the intercellular spaces are closed, the tight junctions show small vesicles and numerous large vacuoles appearing in the cytoplasm.