CA2-INDUCED MITOCHONDRIAL-MEMBRANE PERMEABILIZATION - ROLE OF COENZYME-Q REDOX STATE()

Rotenone-poisoned rat liver mitochondria energized by succinate additi on, after a 5-min period of preincubation in presence of 10 mu M Ca2+, produce H2O2 at much faster rates, undergo extensive swelling, and ar e not able to retain the membrane potential and accumulated Ca2+. Simi lar results were obtained when a suspension of rat liver mitochondria preincubated in anaerobic medium for 5 min was reoxygenated. The addit ion of either ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tet raacetic acid, ruthenium red, catalase, or dithiothreitol, just before succinate or O-2 addition, prevented mitochondrial swelling, indicati ng the involvement of Ca2+, reactive oxygen species, and oxidation of membrane protein thiols in this process of membrane permeabilization. Inhibition of mitochondrial swelling by cyclosporin A suggests that th e membrane alterations observed under these experimental conditions ar e related to opening of the permeability transition pore. The presence of carbonyl cyanide p-trifluoromethoxyphenylhydrazone, which prevents Ca2+ cycling across the membrane, did not inhibit mitochondrial swell ing when Ca2+ influx into the mitochondrial matrix was driven by a hig h Ca2+ gradient. When rotenone plus antimycin A-poisoned mitochondria were energized by N,N,N',N'-tetramethyl-p-phenylenediamine, which redu ces respiratory chain complex IV, mitochondrial swelling did not occur , unless succinate, which reduces coenzyme Q, was also added. It is co ncluded that reduced coenzyme Q is the electron source for oxygen radi cal production during Ca2+-stimulated oxidative damage of mitochondria .