Dexamethasone enhances active cation transport in cultured aortic smooth muscle cells

Previous studies have indicated that ouabain-sensitive cation transport is increased in arteries obtained from rats with glucocorticoid-induced hypertension. However, it remained unclear whether this effect reflected direct glucocorticoid activation or rather depended on the elevated arterial pressure per se. In the present study, we examined the effect of dexamethasone on cultured rat aortic smooth muscle cells. Dexamethasone (10(-9) mol/L) increased ouabain-sensitive 86Rb uptake by about 50% (control: 16.5 +/- 1.6 pmol/mg protein/10 min; dexamethasone 10(-9) mol/L: 24.4 +/- 1.3 pmol/mg protein/10 min). The effect was not apparent until 18 h of incubation and was partly inhibited by the mineralocorticoid antagonist spironolactone. Dexamethasone also increased membrane potential in these cells by an average of 9.5 mV (control: -43.3 +/- 4 mV; dexamethasone: -52.8 +/- 4 mV), presumably reflecting increased intracellular K+ activity as a result of dexamethasone's effect on the Na,K pump. These results suggest a direct effect of glucocorticoids on arterial Na,K pump. The physiopathological significance of this effect remains to be determined.