Effect of Na+ on Na+,K+-ATPase alpha-subunit expression and Na+-pump activity in aortic smooth muscle cells.
In earlier studies we demonstrated that cyclical mechanical strain on vascular smooth muscle cells increases intracellular Na+ and upregulates the alpha-1 and alpha-2 isoform expression of Na+,K+-ATPase, and that the increase of intracellular Na+ and upregulation of the alpha-2 isoform expression are blocked by Gd3+, which blocks entry of ions (including Na+) through stretch-activated channels. The present study was designed to investigate the role of intracellular Na+ in Na+,K+-ATPase regulation by increasing intracellular Na+ with chronic ouabain treatment. In parallel experiments, we measured Na+,K+-ATPase alpha isoform expression, Na+-pump activity and intracellular Na+ in cultured aortic smooth muscle cells after treatment with two concentrations of ouabain for various time periods. Treatment with 100 nM ouabain resulted in a significant elevation in intracellular Na+ after 1 (21%) and 2 h (12%), but the value returned to baseline after 12 h. Both alpha-1 and alpha-2 subunits of Na+,K+-ATPase were significantly upregulated after 1 through 4 days. Na+-pump activity was also stimulated, and the time course of this effect closely followed protein expression. At 200 microM of ouabain, the effects on intracellular Na+, isoform expression and Na+-pump activity at earlier time points (1 h through 1 day) were similar to those with 100 nM treatment, but prolonged treatment (2 and 4 days) resulted in an accumulation of intracellular Na+ and inhibition of the isoform expression and Na+-pump activity, possibly due to general dysfunction of the cells as a result of chronic exposure to high concentrations of ouabain. We conclude that elevated intracellular Na+ can serve as a signal to mediate the alpha isoform upregulation and the regulatory process requires less than one day.
Department of Pharmacology and Experimental Therapeutics, Louisiana State University Medical Center, New Orleans 70112, USA.
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Songu-Mize
D000818:Animals; D001011:Aorta / Q000187:drug effects*; D002478:Cells, Cultured; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005682:Gadolinium / Q000494:pharmacology; D006706:Homeostasis / Q000187:drug effects; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D008297:Male; D009131:Muscle, Smooth, Vascular / Q000187:drug effects*; D010042:Ouabain / Q000494:pharmacology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D012964:Sodium / Q000032:analysis / Q000378:metabolism*; D000254:Sodium-Potassium-Exchanging ATPase / Q000037:antagonists & inhibitors / Q000096:biosynthesis*; D013997:Time Factors; D015854:Up-Regulation
D004791:Enzyme Inhibitors; D007527:Isoenzymes; D010042:Ouabain; D012964:Sodium; D005682:Gadolinium; D000254:Sodium-Potassium-Exchanging ATPase