Functional and biochemical characteristics of mitochondrial fractions from rat liver in cold-induced oxidative stress

We determined characteristics of rat liver mitochondrial fractions, resolved at 1000 (M1), 3000 (M3), and 10,000 g (M10) after 2 and 10 days cold exposure. In all groups, the M1 fraction exhibited the highest oxidative capacity, oxidative damage, H2O2 production rate, and susceptibility to stress conditions, and the lowest antioxidant levels. Cold exposure increased cytochrome oxidase activity in all fractions and succinate-supported O2 consumption in the M1 and M10 fractions during state 3 and state 4 respiration, respectively. With succinate, the H2O2 release rate increased in all fractions during state 4 and state 3 respiration, whereas with pyruvate/malate, it increased only during state 4 respiration. Increases in tissue mitochondrial proteins caused a faster H2O2 flow from the mitochondrial to cytosolic compartment, which was limited by the reduction in the M1 fraction. Despite increased liposoluble antioxidant levels, cold also caused enhanced oxidative damage and susceptibility to oxidative challenge and Ca2+-induced swelling in all fractions. These changes leading to elimination of H2O2-overproducing mitochondria avoided excessive tissue damage. We propose that triiodothyronine, whose levels increase in the cold environment, brings about the biochemical changes producing oxidative damage and those limiting its extent.