Abstract
The impact of vanadate on the Na,K-ATPase system in the vascular smooth muscle cell is poorly understood. The present study describes the kinetics of the effect of vanadate on Na,K-ATPase and the Na-K pump in in vitro grown rat VSMCʼs. Vanadate interaction with the Na,K-ATPase system in vascular smooth muscle cells was examined by observing its influence on ouabain-sensitive adenosine triphosphate hydrolysis in disrupted cells rendered permeable by osmotic shock, and the uptake of rubidium by intact cells. The I50 for vanadate inhibition of ouabain-sensitive hydrolysis of adenosine triphosphate occurred at vanadate concentrations of 10−* to 10″ M. This inhibition was potassium dependent. The maximal inhibitory effect of vanadate occurred at potassium concentrations of 10–20 mEq/liter. Sodium exerted a moderate antagonistic influence on vanadate inhibition of ouabain-sensitive adenosine triphosphate hydrolysis. Rubidium uptake by vascular smooth muscle cells was not altered within 120 minutes when 10− M vanadate was added to the medium containing intact vascular smooth muscle cells. Yet, vanadium concentrations in the vascular smooth muscle cells within this incubation period reached levels 1.48-fold higher than the extracellular vanadate concentrations of 10″ M. These observations indicate that vanadate is a potent inhibitor of the VSMC Na,K-ATPase in disrupted vascular smooth muscle cells. However, in intact vascular smooth muscle cells vanadium gaining access into the vascular smooth muscle cellʼs interior does not inhibit the Na-K pump, probably because of its binding to intracellular proteins and/or conversion from the vanadate to the vanadyl ion.