| Abstract: | We have identified a group of proteins (Mr approximately 70000-80000; pI approximately 5.8-6.4) in giant-toad (Bufo marinus) urinary-bladder epithelial cells whose synthesis appears to be related to aldosterone-stimulated Na+ transport. To define this relationship further, we examined whether submaximal natriferic concentrations of aldosterone induced these proteins and whether spironolactone (a specific mineralocorticoid antagonist in renal epithelia) inhibited their synthesis. Short-circuit current was used to measure Na+ transport and epithelial-cell protein synthesis was detected with high-resolution two-dimensional polyacrylamide-gel electrophoresis and autoradiography. Submaximal natriferic concentrations of aldosterone (1.4 X 10(-8) M) induced the same proteins as maximal concentrations of the hormone (1.4 X 10(-7) M). In contrast, in previous experiments, similar proteins were not induced by subnatriferic concentrations (5.0 X 10(-8) M) of cortisol, a glucocorticoid. A spironolactone/aldosterone molar ratio of 2000:1 was required to inhibit aldosterone-stimulated Na+ transport completely; ratios of 200:1 and 500:1 produced partial inhibition. Concentrations of spironolactone that abolished aldosterone-stimulated Na+ transport also inhibited aldosterone-induced protein synthesis. We conclude that the synthesis of the proteins we have identified is specifically related to activation of the mineralocorticoid pathway. |
