Peroxovanadate inhibits Ca2+ release from mitochondria

Mitochondria contain a specific Ca2+ release pathway which operates when oxidized mitochondrial pyridine nucleotides are hydrolyzed. NAD+ hydrolysis and therefore Ca2+ release is possible when some vicinal thiols are cross-linked. Here we report that the thiol oxidant peroxovanadate inhibits the specific Ca2+ release pathway. In mitochondria, peroxovanadate causes a complete loss of reduced glutathione, which is not accompanied by formation of glutathione disulfide, and a partial loss of protein thiols. In model reactions, peroxovanadate oxidizes reduced glutathione predominantly to the sulfonate derivative, but does not react with glutathione disulfide. When the vicinal thiols relevant for Ca2+ release are cross-linked, Ca2+ release is no longer inhibited by peroxovanadate. Conversely, pretreatment of mitochondria with peroxovanadate makes them insensitive to compounds promoting the disulfide state. These results suggest that peroxovanadate inhibits the prooxidant-induced Ca2+ release from mitochondria by (i) depleting mitochondria of reduced glutathione and (ii) oxidizing the vicinal thiols relevant for Ca2+ release to a state higher than disulfide, presumably the sulfonate state. The findings provide further insight into the regulation of Ca2+ release from intact mitochondria, and may be relevant for a better understanding of the action of peroxovanadate in cells, where the compound can be insulin mimetic.