Reoxygenation-Induced Mitochondrial Damage is Caused by the Ca 2-Dependent Mitochondrial Inner Membrane Permeability Transition

Abstract

Anoxia/reoxygenation injury of isolated rat liver mitochondria was investigated. During anoxia of up to 60 min, the membrane potential was largely preserved and mitochondrial swelling was not observed. Reoxygenation of anoxic mitochondria rapidly caused swelling, cyclosporin A-sensitive Ca 2+ efflux, [ 14C]sucrose trapping, and loss of the membrane potential along with increased generation of reactive oxygen intermediates (ROI). Although pretreatment with catalase and superoxide dismutase completely abolished reoxygenation-induced generation of ROI, mitochondrial damage was not prevented, as indicated by swelling, loss of the membrane potential, a decrease of the ATP content, and cyclosporin A-sensitive Ca 2+ efflux. However, addition of the immunosuppressant cyclosporin A or addition of ADP completely prevented the mitochondrial damage induced by reoxygenation. The same protective effect was noted when Ca 2+ cycling was prevented, either by chelating Ca 2+ with EGTA or by inhibiting Ca 2+ reuptake with ruthenium red. These findings indicate that mitochondrial anoxia/reoxygenation injury is caused by the cyclosporin A-sensitive and Ca 2+-dependent membrane permeability transition. In contrast, reoxygenation injury does not appear to be triggered by the enhanced production of ROI.