Changes in sodium pool and kinetics of sodium transport in frog skin produced by amiloride.

1. Amiloride produces a decrease in size of the active sodium transport pool of isolated frog skin.2. Rate coefficients for sodium movement into and out of the transporting cells across the outside membrane are decreased by amiloride. The rate coefficient for sodium extrusion across the inside membrane is not significantly affected.3. In the presence and in the absence of amiloride, the relation of sodium transport to outside sodium concentration exhibits similar saturation kinetics but amiloride reduces sodium transport rate at every sodium concentration of the outside solution.4. Labelling of skin with (14)C-amiloride from the outside solution is significantly greater than labelling with (14)C-inulin.5. The results of these studies suggest that amiloride reacts with sites on the outside membrane of the transporting cells as a result of which the rate of sodium movement across this membrane is diminished.