Vanadate effect on the Na,K-ATPase and the Na-K pump in in vitro-grown rat vascular smooth muscle cells.

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 VSMC's. 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(-6) to 10(-7) 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(-5) 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(-5) 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 cell's 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.

Effects of soldium vanadate on the smooth muscle of the guinea-pig vas deferens.

“…Sodium vanadate also caused tension development in the presence of high concentration of ouabain, as has been reported in vascular smooth muscles (Ozaki & Urakawa, 1979 ;Hudgins & Bond, 1981;Rapp, 1981). Moreover, it has been reported that even though vanadate is taken into vascular smooth muscle cells, there is no inhibition of Na, K-ATPase (Searle et al, 1983). This also supports the contractile action of vanadate without inhibition of N a, K-ATPase.…”

Inhibitory effects of genistein on ATP‐sensitive K+ channels in rabbit portal vein smooth muscle

“…The IC 50 value observed in the present experiments with genistein on the ATP-sensitive K + channel corresponds well to those previously obtained. To judge from the present and other experiments on sodium orthovanadate, a tyrosine phosphatase inhibitor as well as a blocker of Na + -K + ATPase and Ca 2+ ATPase (Searle et al, 1983;Raeymaekers et al, 1983), current augmentation by vanadate is not speci®c to the voltage-dependent Ca 2+ channel, but also a ects various K + currents, including the pinacidil-induced K + current in vascular smooth muscle cells (Wijetunge et al, 1992;Xiong & Cheung, 1995;Hatakeyama et al, 1996). Augmentation of such ionic currents by orthovanadate and their inhibition by genistein, but not by daidzein, is fully consistent with the e ects being produced via tyrosine phosphorylation.…”

Clearance of store-released Ca2+by the Na+-Ca2+exchanger is diminished in aortic smooth muscle from Na+-K+-ATPase α2-isoform gene-ablated mice

“…Vanadate can also inhibit SERCA and H ϩ pumps; however, with our protocol, SERCA was already inhibited by CPA and no effect of vanadate on cell pH was observed over the experimental time course (data not shown). Another consideration in using vanadate is its ability to permeate the cell (25); however, treatment with vanadate clearly altered Ca 2ϩ clearance, indicating at least partial effects on PMCA. Thus, with the caveat that no inhibitor is perfectly specific, our evidence suggests that the effects of vanadate reported here reflect the inhibition of PMCA.…”