Na+, K(+)-adenosine triphosphatase regulation in hypertrophied vascular smooth muscle cells

Vascular smooth muscle cell hypertrophy is a normal compensatory state that may play a pathogenic role in hypertension. Angiotensin II stimulates a hypertrophic response in cultured vascular smooth muscle cells. As part of the growth response, angiotensin II rapidly activates the Na(+)-H+ exchanger, increasing Na+ influx. Because Na+, K(+)-ATPase is the major cellular mechanism for regulating intracellular Na+, we studied the effects of angiotensin II-induced hypertrophy on Na+, K(+)-ATPase expression and activity. Angiotensin II caused rapid increases in both steady-state Na+, K(+)-ATPase activity (ouabain-sensitive 86Rb uptake) and intracellular [Na+]. Angiotensin II also caused a sustained increase in Na+, K(+)-ATPase at 24 hours with a 73% increase in maximal 86Rb uptake per milligram protein and a fourfold increase in Na+, K(+)-ATPase alpha-1 messenger RNA levels. Thus, angiotensin II hypertrophy was associated with rapid increases in Na+, K(+)-ATPase activity due to increased Na+ entry and sustained increases due to a specific increase in Na+, K(+)-ATPase expression. These data demonstrate dynamic regulation of Na+, K(+)-ATPase at the functional and molecular level and suggest that similar compensatory mechanisms should be present in vivo. Alterations in such compensatory pathways may be fundamental to the pathogenesis of hypertension.