Salt-induced Na⁺/K⁺-ATPase-α/β expression involves soluble adenylyl cyclase in endothelial cells

High dietary salt intake may lead to vascular stiffness, which predicts cardiovascular diseases such as heart failure, and myocardial and cerebral infarctions as well as renal impairment. The vascular endothelium is a primary target for deleterious salt effects leading to dysfunction and endothelial stiffness. We hypothesize that the Ca²⁺- and bicarbonate-activated soluble adenylyl cyclase (sAC) contributes to Na⁺/K⁺-ATPase expression regulation in vascular endothelial cells and is an important regulator of endothelial stiffness. In vitro stimulation of vascular endothelial cells with high sodium (150 mM Na⁺)-induced Na⁺/K⁺-ATPase-α and Na⁺/K⁺-ATPase-β protein expression determined by western blot. Promoter analyses revealed increased cAMP response element (CRE)-mediated Na⁺/K⁺-ATPase-α transcriptional activity under high sodium concentrations. Inhibition of sAC by the specific inhibitor KH7 or siRNA reduced the sodium effects. Flame photometry revealed increased intracellular sodium concentrations in response to high sodium stimulations, which were paralleled by elevated ATP levels. Using atomic force microscopy, a nano-technique that measures cellular stiffness and deformability, we detected significant endothelial stiffening under increased sodium concentrations, which was prevented by inhibition of sAC using KH7 and Na⁺/K⁺-ATPase using ouabain. Furthermore, analysis of primary aortic endothelial cells in an in vitro aging model revealed an impaired Na⁺/K⁺-ATPase-α sodium response and elevated intracellular sodium levels with cellular aging. We conclude that sAC mediates sodium-induced Na⁺/K⁺-ATPase expression in vascular endothelium and is an important regulator of endothelial stiffness. The reactivity of Na⁺/K⁺-ATPase-α expression regulation in response to high sodium seems to be impaired in aging endothelial cells and might be a component of endothelial dysfunction.