Aldosterone Regulates the Na-K-2Cl Cotransporter in Vascular Smooth Muscle

Abstract

Aldosterone increases cation transport and contractility of vascular smooth muscle, but the specific transporter involved and how it is linked to smooth muscle tone is unknown. Because the Na-K-2Cl cotransporter (NKCC1) contributes to vascular smooth muscle contraction and is regulated by vasoactive compounds, we sought to determine whether this transporter is a target of aldosterone in rat aorta. Treatment of adrenalectomized rats with aldosterone for 7 days resulted in a 63% increase in NKCC1 activity as measured by bumetanide-sensitive efflux of ⁸⁶ Rb ⁺ . Treatment of normal aortas in culture with aldosterone for 3 and 7 days resulted in 29% and 47% increases in NKCC1 activity, respectively. Aldosterone had no acute effect on ⁸⁶ Rb ⁺ efflux. Stimulation of NKCC1 was blocked by spironolactone, a mineralocorticoid receptor antagonist, but not by RU38486, a glucocorticoid receptor antagonist. Aldosterone did not augment the stimulation of NKCC1 by phenylephrine and did not increase NKCC1 mRNA as determined by real-time polymerase chain reaction. We conclude that aldosterone regulates the Na-K-2Cl cotransporter in vascular smooth muscle through classic mineralocorticoid receptors but not through changes in the abundance of NKCC1 mRNA. This could account for the increase in Na ⁺ , K ⁺ , and Cl ⁻ fluxes previously observed in vascular smooth muscle from mineralocorticoid-treated animals and may contribute to increased vascular tone.