Aldosterone-mediated regulation of Na+, K(+)-ATPase gene expression in adult and neonatal rat cardiocytes.
By altering the Na+/K+ electrochemical gradient, Na+,K(+)-ATPase activity profoundly influences cardiac cell excitability and contractility. The recent finding of mineralocorticoid hormone receptors in the heart implies that Na+,K(+)-ATPase gene expression, and hence cardiac function, is regulated by aldosterone, a corticosteroid hormone associated with certain forms of hypertension and classically involved in regulating Na+,K(+)-ATPase gene expression and transepithelial Na+ transport in tissues such as the kidney. The regulation by aldosterone of the major cardiac Na+,K(+)-ATPase isoform genes, alpha-1 and beta-1, were studied in adult and neonatal rat ventricular cardiocytes grown in defined serum-free media. In both cell types, aldosterone-induced a rapid and sustained 3-fold induction in alpha-1 mRNA accumulation within 6 h. beta-1 mRNA was similarly induced. alpha-1 mRNA induction occurred over the physiological range with an EC50 of 1-2 nM, consistent with binding of aldosterone to the high affinity mineralocorticoid hormone receptor. In adult cardiocytes, this was associated with a 36% increase in alpha subunit protein accumulation and an increase in Na(+)-K(+)-ATPase transport activity. Aldosterone did not alter the 3-h half-life of alpha-1 mRNA, indicating an induction of alpha-1 mRNA synthesis. Aldosterone-dependent alpha-1 mRNA accumulation was not blocked by the protein synthesis inhibitor cycloheximide, whereas amiloride inhibited both an aldosterone-dependent increase in intracellular Na+ [Na+]i) and alpha-1 mRNA accumulation. This demonstrates that aldosterone directly stimulates Na+,K(+)-ATPase alpha-1 subunit mRNA synthesis and protein accumulation in cardiac cells throughout development and suggests that the heart is a mineralocorticoid-responsive organ. An early increase in [Na+]i may be a proximal event in the mediation of the hormone effect.
Ikeda
U
U
Department of Medicine, Emory University School of Medicine, Atlanta, Georgia 30322.
Hyman
R
R
Smith
T W
TW
Medford
R M
RM
D000375:Aging / Q000378:metabolism*; D000450:Aldosterone / Q000502:physiology*; D000584:Amiloride / Q000494:pharmacology; D000818:Animals; D015152:Blotting, Northern; D002478:Cells, Cultured; D003513:Cycloheximide / Q000494:pharmacology; D003609:Dactinomycin / Q000494:pharmacology; D004790:Enzyme Induction; D005434:Flow Cytometry; D015971:Gene Expression Regulation, Enzymologic / Q000187:drug effects*; D007700:Kinetics; D009206:Myocardium / Q000166:cytology / Q000201:enzymology*; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains; D000254:Sodium-Potassium-Exchanging ATPase / Q000096:biosynthesis / Q000235:genetics*
D011500:Protein Synthesis Inhibitors; D012333:RNA, Messenger; D003609:Dactinomycin; D000450:Aldosterone; D000584:Amiloride; D003513:Cycloheximide; D000254:Sodium-Potassium-Exchanging ATPase