Effects of vanadium on different adenosinetriphosphatases and binding of 3H-labeled ouabain and calcium-45 to rat brain synaptosomes.
The effect of vanadium chloride on rat brain synaptosomal adenosinetriphosphatase (ATPase) activities was determined in vitro and in rats treated at 1 mg/kg.d ip and 10 mg/kg.d po for 10 d. Additional experiments were conducted to determine the effect of vanadium chloride on binding of [3H] ouabain and 45Ca to rat brain synaptosomes. Na+ + K+ - and Ca2+-ATPase activities were inhibited significantly in a concentration-dependent manner by V in vitro. Mg2+ -ATPase inhibition was neither dose-dependent nor significant except at 10(-5) M. Na+ + K+ -ATPase inhibition by V was more pronounced than that of other ATPases studied. Vanadium inhibited [3H] ouabain binding to synaptosomes by 90% at 10(-3) M; the inhibition was concentration-dependent. Binding of 45Ca was inhibited 50% at 10(-4) M; but concentration-dependent inhibition was not evident. Rats treated with vanadium chloride neither became myotonic nor showed any changes in ATPase activities or binding of [3H] ouabain and 45Ca to brain synaptosomes. Lineweaver-Burke plots of the in vitro inhibition of Na+ + K+ -ATPase and [3H] ouabain binding revealed that (1) Na+ + K+ -ATPase activation by ATP was inhibited by V with an increase in Km and a decrease in Vmax; (2) Na+ activation was inhibited noncompetitively by V, as evidenced by a decrease in Vmax and no change in Km; (3)K+ activation was inhibited by V with a decrease in both Vmax and Km; (4) noncompetitive inhibition of Mg2+ -ATPase by V was observed; and (5) the kinetic behavior of [3H] ouabain binding inhibition by V with respect to ATP and Na+ activation was mixed and noncompetitive, respectively. These results suggest that V is a potent inhibitor of Na+ + K+ -ATPase activity in rat brain synaptosomes.
D000251:Adenosine Triphosphatases / Q000037:antagonists & inhibitors*; D000818:Animals; D001921:Brain / Q000187:drug effects / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism*; D066298:In Vitro Techniques; D007700:Kinetics; D008297:Male; D009222:Myotonia / Q000139:chemically induced; D010042:Ouabain / Q000378:metabolism*; D051381:Rats; D011919:Rats, Inbred Strains; D013574:Synaptosomes / Q000378:metabolism*; D014639:Vanadium / Q000633:toxicity*
D014639:Vanadium; D010042:Ouabain; D000251:Adenosine Triphosphatases; D002118:Calcium