H2O2 production and response to stress conditions by mitochondrial fractions from rat liver

Rat liver mitochondria, in different steps of the maturation process, were resolved by differential centrifugation at 1000g (M-1), 3000g (M-3), and 10,000g (M-10), and their characteristics determining susceptibility to stress conditions were investigated. Some parameters did not show gradual changes in the transition from M-10 to M-1 fraction because of the contamination of the M-10 fraction by microsomes and damaged mitochondria with relatively high lipid content. The highest and lowest rates Of 02 consumption and H2O2 production were exhibited by M-1 and M-10 fractions, respectively. Vitamin E and coenzyme Q levels were significantly higher in M-10 than in M, fraction, whereas whole antioxidant capacity was not significantly different. The degree of oxidative damage to lipids and proteins was higher in M-1 and not significantly different in M-3 and M-10 fractions. The order of susceptibility to both oxidative challenge and Ca2+-induced swelling was M-1 > M-3 > M-10. It seems that the Ca2+-induced swelling is due to permeabilization of oxidatively altered inner membrane and leads to discard mitochondria with high ROS production. If, as previous reports suggest, mitochondrial damage is initiating stimulus to mitochonchial biogenesis, the susceptibility of the M, mitochondria to stressful conditions could be important to regulate cellular ROS production. In fact, it should favor the substitution of the oldest ROS-overproducing mitochondria with neoformed mitochondria endowed with a smaller capacity to produce free radicals.