Reduction of Vanadate by Ascorbic Acid and Noradrenaline in Synaptosomes

Abstract

The effect of ascorbic acid [AA] and noradrenaline [norepinephrine, NE] on the inhibition of rat synaptosomal membrane ATPase by vanadate [V] was studied. AA (2 .times. 10-3 M) and NE (10-4 M) partly reversed the inhibition by V (10-6 M); however, when both were administered together the inhibition was completely eliminated. Using ESR spectroscopy, AA (10-3 M) caused a 42% reduction of V (10-4 M). NE (10-4 M) alone also reduced V (10-4 M) partially. When AA and NE were present together all the V was reduced to vanadyl. The concentration of AA present in the brain under physiological conditions identical to that found effective in these experiments. AA may protect the ATPase, at least in part, from inhibition by vanadate as a consequence of reducing V to vanadyl. In those tissues where NE is also present a complete reduction of endogenous vanadium can be presumed.