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 and 10 mg/kg 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 10-5M. 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. Line-weaver-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 K/sub m/ and a decrease in V/sub max/; (2) Na+ activation was inhibited noncompetitively by V, as evidenced by a decrease in V/sub max/ and no change in K/sub m/; (3) K+ activation was inhibited by V with a decrease in both V/sub max/ and K/sub m/; (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