| dc.description | Ca2+-loaded rat liver mitochondria treated with 3,5,3'-triiodothyronine (T-3) undergo nonspecific inner membrane permeabilization, as evidenced by mitochondrial swelling, a decrease in membrane potential (Delta Psi), and an increase in the rate of oxygen uptake, T-3 analogues thyroxine (T-4), 3',5'-diiodothyronine (T-2), and 3,5',3'-triiodothyronine (reverse T-3), in decreasing order of potency, resulted in a similar but less extensive effect. Permeabilization induced by T-3 is dependent on Ca2+ (1 mu M) and T-3 (0.5-25 mu M) concentrations and is inhibited by cyclosporin A, a known inhibitor of mitochondrial permeability transition. Catalase or dithiothreitol also prevents membrane permeabilization, suggesting the participation of membrane protein thiol group oxidation induced by reactive oxygen species, The determination of the mitochondrial membrane protein thiol group content after treatment with Ca2+ and T-3 shows a significant decrease, due to thiol oxidation, When mitochondria are incubated in the presence of inorganic phosphate and the protonophore carbonyl cyanide p-trifluoromethoxyphenylhydrazone, mitochondrial swelling still occurs after treatment with T-3 and high Ca2+ concentrations, suggesting that mitochondrial permeabilization is not dependent on T-3-induced Delta Psi or matrix pH alterations, Under these experimental conditions, when no oxygen is present in the incubation medium, no permeabilization occurs, suggesting that the permeabilization is dependent on mitochondrial-generated reactive oxygen species, Confirming this hypothesis, superoxide generation in a suspension of submitochondrial particles is increased when T-3 is present, Our results lead to the conclusion that T-3 induces a situation of oxidative stress in isolated liver mitochondria, with Ca2+-mediated membrane protein thiol oxidation and nonspecific inner membrane permeabilization. (C) 1998 Academic Press. | |
