PERMEABILIZATION OF THE INNER MITOCHONDRIAL-MEMBRANE BY CA2-BUTYL HYDROPEROXIDE AND MEDIATED BY REACTIVE OXYGEN SPECIES GENERATED BY MITOCHONDRIA( IONS IS STIMULATED BY T)

The extent of swelling undergone by deenergized mitochondria incubated in KCl/sucrose medium in the presence of Ca2+ alone or Ca2+ and t-but yl hydroperoxide decreases by decreasing molecular oxygen concentratio n in the reaction medium; under anaerobiosis no swelling occurs. This swelling is also inhibited by the presence of exogenous catalase or by the Fe2+ chelator o-phenanthroline in a time-dependent manner. The pr oduction of protein thiol cross-linking that leads to the formation of protein aggregates induced by Ca2+ and t-butyl hydroperoxide does not occur when mitochondria are incubated in anaerobic medium or in the p resence of o-phenanthroline. In addition, it is also shown that the yi eld of stable methyl radical adducts, obtained from rat liver mitochon dria treated with t-butyl hydroperoxide and the spin trap DMPO, is red uced by addition of EGTA and increases by addition of Ca2+ ions. These data support the hypothesis that Ca2+ ions stimulate electron leakage from the respiratory chain, increasing the mitochondrial production o f reactive oxygen species.