Effects of vanadium on different adenosinetriphosphatases and binding of3H‐labeled ouabain and calcium‐45 to rat brain synaptosomes

Abstract

The effect of vanadium chloride on rat brain synaptosomal ATPase activities was determined in vitro and in rats treated at 1 mg/kg per day i.p. and 10 mg/kg per day orally for 10 days. 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 not dose-dependent or significant except at 10-5 M. Na+ + K+-ATPase inhibition by V was more pronounced than that of other ATPases. V 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 did not become myotonic or show 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 the following characteristics: Na+ + K+-ATPase activation by ATP was inhibited by V with an increase in Km and a decrease in Vmax; Na+ activation was inhibited noncompetitively by V, as evidenced by a decrease in Vmax and no change in Km; K+ activation was inhibited by V with a decrease in Vmax and Km; noncompetitive inhibition of Mg2+-ATPase by V was observed; and the kinetic behavior of [3H]ouabain binding inhibition by V with respect to ATP and Na+ activation was mixed and noncompetitive, respectively. V was a potent inhibitor of Na+ + K+-ATPase activity in rat brain synaptosomes.