Role of Na+ and Ca2+ in stretch-induced Na+-K+-ATPase α-subunit regulation in aortic smooth muscle cells

Abstract

This study was designed to test the role of Na+ and Ca2+ entry in the stretch-induced Na+-K+-ATPase α1- and α2-isoform upregulation observed in our previous studies. We measured intracellular Na+ in cyclically stretched rat aortic smooth muscle cells, with or without gadolinium treatment, for various durations and performed Western blotting to analyze the effects of stretch and the calcium channel blocker isradipine on the expression of α-isoforms. Intracellular Na+was elevated significantly after 1- and 2-h stretch, but returned to baseline after 1-, 2-, and 4-day stretch. This increase in intracellular Na+ was blocked by gadolinium. Both α1- and α2-isoforms were upregulated after either 2 or 4 days of cyclical stretch. Isradipine had no apparent effect on stretch-induced upregulation on either α-isoform, thus suggesting that Ca2+ entry through L-type channels is not involved in the stretch-induced upregulation. We therefore conclude that a transient intracellular Na+ elevation during stretch may serve as a signal to mediate the α1- and α2-isoform upregulation.