Accelerated RNA turnover in toad urinary bladder epithelial cells during early aldosterone action

Demonstration of increased nuclear RNA specific radioactivity in epithelial cells scraped from isolated toad urinary bladder after brief treatment with aldosterone is shown to depend on the quantity of exogenous uridine supplied. By comparing the rate of incorporation of the nucleoside [6-3H] uridine into nuclear RNA at two different exogenous uridine concentrations, an estimate of the relative contribution of exogenous and endogenous nucleoside to the intracellular precursor pool was obtained. Based upon such an experimental model, we found that aldosterone significantly increased the contribution from endogenous precursor and conclude that one effect of the steroid in this isolated tissue is to accelerate RNA turnover. Accelerated RNA turnover, resulting from hormone treatment, was further substantiated by demonstarting a significant decrease in [6-3H] uridine concentration of the precursor pool of prelabeled cells following unlabeled uridine chase. Although evaluated, no evidence for aldosterone increasing the uptake of [6-3H] uridine into the acid-soluble precursor pool was found. In addition, the uridine concentration was shown not to be a rate-limiting step for the bioelectric demonstration of aldosterone-stimulated active Na+ transport.