Amiloride and the mode of action of aldosterone on sodium transport across toad bladder and skin

Summary The characteristics of the inhibitory influence exerted by amiloride on active sodium transport by toad bladder and skin were taken advantage of to shed additional light on the mechanism whereby hormones-chiefly aldosterone-stimulate sodium transport across such epithelia.Toad skin treated with amiloride was as responsive to vasopressin and to aldosterone as the matched control preparation, while the response of toad skin to insulin was blunted under similar circumstances.When aldosterone-stimulated toad skin was exposed to amiloride, the resulting depression of sodium-transporting activity was less pronounced than was the case with matched control; on the other hand, insulin-treated membranes were as sensitive to amiloride as matched controls. Similar observations were made with triamterene.This is taken to indicate that the density of the permeases apparently required for sodium to cross the apical cell border of these specialized epithelia, is increased under the influence of aldosterone.The affinity of amiloride for toad bladder tissue was not influenced by aldosterone, as indicated by tissue labelling experiments.On leave of absence from the University of Chicago, Department of Medicine. Recipient of a U.S.P.H.S. Career Development Award K2-GM21.842.