Muscosal and serosal effects of insulin on ion contents of the frog urinary bladder.

When applied in vitro at the serosal border of the bladder of Rana temporaria insulin (1.7.10(-5) M) brings about a decrease in the tissue sodium content, suggesting a stimulation of the pump extruding sodium ions from epithelial cells. On the other hand, the application of insulin at the two sides of the bladder results in a significant increase of the sodium content of the tissue. It is hence concluded that the contact of the hormone with the mucosal membranes of the epithelial cells of the bladder enhances sodium entry across the membranes. The effect if so pronounced that it obscures the stimulation of the pumps localized at the opposite pole of the cells.