The effect of temperature and substrate concentration on the kinetics of (6- 3 H)uridine incorporation into RNA of toad bladder epithelial cells: the role of aldosterone

Role of RNA in the action of aldosterone on Na+ transport

Recent data describing the effects of aldosterone on the induction of messenger RNA (= mRNA) and ribosomal RNA (= rRNA) are reviewed. In the urinary bladder of the toad, aldosterone induces a few specific polyadenylated mRNAs (= poly(A)(+)mRNA) during the latent period, i.e., 30 to 60 min after hormone addition. Later i.e., 90 to 240 min after aldosterone addition, 18S and 28S cytoplasmic rRNA subunits are also induced. The effect of poly(A)(+)mRNA is mineralocorticoid-specific and correlates well with the aldosterone-dependent Na+ transport. Actinomycin D which inhibits both poly(A)(+)mRNA and nonpolyadenylated mRNA (= POLY(A)(-)mRNA) totally abolishes the response to aldosterone on Na+ transport. 3'deoxyadenosine (cordycepin), which inhibits poly(A)(+)mRNA but not poly(A)(-)mRNA, only inhibits 50 to 60% of the physiological response. These differential effects suggest that an intact poly(A)(-)mRNA pathway is also an important factor in mediating the action of aldosterone. In contrast, 3'deoxycytidine, which inhibits rRNA but not mRNA, does not impair the mineralocorticoid response, at least during the first 3 hr of aldosterone action.

Kinetics of RNA labeling in toad bladder epithelium: effects of aldosterone and related steroids

Sucrose gradient analysis revealed an aldosterone-dependent increase in the incorporation of [(3)H]uridine into a nonmethylated, rapidly labeled RNA that sedimented at 9-12 S. This effect was antagonized by an anti-mineralocorticoid, spironolactone (SC 9420), and was not elicited either by a glucocorticoid, cortisol, or by the inactive isomer, 17-alpha-isoaldosterone. These findings are in accord with the inference that mRNA is induced by aldosterone during the latent period and that the induced mRNA mediates the action on sodium transport.