REGULATION OF NA-K-ATPASE GENE-EXPRESSION BY ALDOSTERONE IN VASCULAR SMOOTH-MUSCLE CELLS

Na-K-adenosinetriphosphatase (ATPase) activity profoundly influences v ascular cell excitability, contractility, and volume regulation. The r ecent finding of mineralocorticoid hormone receptors in vascular tissu e suggests the possibility that Na-K-ATPase gene expression in vascula r tissue is regulated by the mineralocorticoid aldosterone. In this st udy, we investigated Na-K-ATPase gene expression by aldosterone in cul tured rat vascular smooth muscle cells (VSMC). Na-K-ATPase alpha1- and beta1-isoform mRNAs, but not alpha2- and alpha3-isoform mRNAs, were e xpressed in cultured rat VSMC. Aldosterone caused a 2.3-fold increase in the alpha1 mRNA and a 4.7-fold increase in the beta1 mRNA accumulat ion with peak elevations at 24 and 6 h, respectively. Aldosterone indu ced the alpha1 mRNA expression at physiological concentrations (half-m aximum effective concentration = 2-3 nM), consistent with the binding of aldosterone to mineralocorticoid hormone receptors. The augmented a lpha1 mRNA expression by aldosterone was associated with a twofold inc rease in the alpha1-subunit protein accumulation. Pretreatment of VSMC with cycloheximide caused a 10-fold increase in the alpha1 mRNA expre ssion, and the aldosterone-mediated alpha1 mRNA accumulation was not o bserved in the presence of cycloheximide. Transfection experiments wit h the luciferase reporter gene revealed that aldosterone response sequ ences are located within the 5'-flanking regions of the alpha1-isoform gene. These data demonstrate that the mineralocorticoid aldosterone d irectly stimulates Na-K-ATPase gene expression and protein accumulatio n in VSMC.