| Abstract: | Aldosterone-stimulated Na+ transport is mediated by new protein synthesis, but the identification of specific aldosterone-induced proteins (AIPs) has proven difficult and the cellular function of such proteins is unknown. Using high resolution two-dimensional polyacrylamide gel electrophoresis and autoradiography we have identified AIPs of similar isoelectric points (5.8 to 6.4) and molecular weights (70,000 to 80,000) in membrane-rich and cytosolic subcellular fractions of epithelial cells derived from single toad urinary bladders. The ability of actinomycin D to inhibit both AIP synthesis and aldosterone-induced Na+ transport is consistent with a role for these proteins in the natriferic action of aldosterone. In addition, since non-natriferic concentrations of cortisol did not induce similar proteins, AIP synthesis appears to be mineralocorticoid-specific. The relationship of AIP synthesis to Na+ transport was also studied. Since amiloride, which blocks Na+ transport in high resistance epithelia, did not affect the synthesis of these proteins, Na+ transport is not required for their synthesis. In addition, similar proteins were not induced when Na+ transport was stimulated by antidiuretic hormone and theophylline. Consequently, AIP synthesis is not merely a nonspecific consequence of the cellular metabolic changes associated with Na+ transport. |
