Induction of transporting sites in a sodium transporting epithelium.

1. Frogs (Rana temporaria) were bathed for 1 week in solutions containing 1-1 mM sodium chloride and either one or both of amiloride (10(-4)M) and spironolactone (10(-5r both of amiloride (10(-4) M) and spironolactone (10(-5) M). This procedure was designed to deplete the sodium transporting compartment of the skin epithelium of sodium, while at the same time antagonizing the effects of endogenous aldosterone. 2. After 1 week the skins were used in vitro to measure the level of sodium transport (short-circuit current) and the density of sodium entry sites in the mucosal surface of the epithelium ([14C]amiloride binding). 3. Sodium deprivation for 1 week caused approximately a doubling of both sodium transport and the density of sodium entry sites in the mucosal surface of the epithelium compared to control skins. 4. When the results for sodium deprived and control skins were pooled there was a highly significant correlation between the density of sodium entry sites and sodium transport. 5. Mechanisms by which sodium deprivation leads to an increase in the density of sodium entry sites are discussed.