Ca2+ induces a cyclosporin A-insensitive permeability transition pore in isolated potato tuber mitochondria mediated by reactive oxygen species

Oxidative damage of mammalian mitochondria induced by Ca2+ and prooxidants is mediated by the attack of mirochondria-generated reactive oxygen species on membrane protein thiols promoting oxidation and cross-linkage that lead s to the opening of the mitochondrial permeability transition pore (Castilh o et al., 1995). In this study, we present evidence that deenergized potato tuber (Solanum tuberosum) mitochondria, which do not possess a Ca2+ unipor t, undergo inner membrane permeabilization when treated with Ca2+ (>0.2 mM) , as indicated by mitochondrial swelling. Similar to rat liver mitochondria , this permeabilization is enhanced by diamide, a thiol oxidant that create s a condition of oxidative stress by oxidizing pyridine nucleotides. This i s inhibited by the antioxidants catalase and dithiothreitol. Potato mitocho ndrial membrane permeabilization is not inhibited by ADP, cyclosporin A, an d ruthenium red, acid is partially inhibited by Mg2+ and acidic pH, well kn own inhibitors of the mammalian mitochondrial permeability transition. The lack of inhibition of potato mitochondrial permeabilization by cyclosporin A is in contrast to the inhibition of the peptidylprolyl cis-trans isomeras e activity, that is related to the cyclosporin A-binding protein cyclophili n. Interestingly, the monofunctional thiol reagent mersalyl induces an exte nsive cyclosporin A-insensitive potato mitochondrial swelling, even in the presence of lower Ca2+ concentrations (>0.01 mM). In conclusion, we have id entified a cyclosporin A-insensitive permeability transition pore in isolat ed potato mitochondria that is induced by reactive oxygen species.