Mitochondrial Respiration Is Associated with Alloxan-Induced Mitochondrial Permeability Transition

We previously showed that increased mitochondrial inner membrane permeability which is known as mitochondrial permeability transition (MPT) is triggered by adding succinate in the presence of the diabetogenic agent alloxan. Here, our aim was to investigate whether mitochondrial respiration is associated with alloxan-induced MPT. After mitochondria isolated from rat liver were incubated with alloxan at 37°C for 5 min, the addition of succinate immediately triggered the MPT in the presence of rotenone. However, little or no induction occurred at incubation temperatures below 25°C. Malate/glutamate also triggered MPT by alloxan in the absence of rotenone. In mitochondrial suspensions containing alloxan, succinate accelerated oxygen consumption that was completely inhibited by cyanide. These results suggest that mitochondrial respiration is associated with the alloxan-induced MPT. Alloxan radical production was investigated using ESR spectroscopy. Mitochondria incubated with succinate and alloxan elicited low signal intensity (radical formation) that increased significantly in the presence of cyanide. When the incubation of alloxan with mitochondria after the addition of succinate, a little intensity of the signal was observed, but it was remarkably increased after the addition of cyanide. Ubiquinone analogues inhibited the MPT induction. These results suggest that the initiation of MPT is associated with alloxan redox cycling via an electron transfer process at a quinone-binding site in respiratory mitochondria.