Free radical mechanisms of cytotoxic cardiac damage and possibilities of their pharmacological correction

97 MECHANISMS OF SUPEROXIDE FORI;IATION IN THE bcl COMPLEX OF THE MITOCHONDRIAL RESPIRATORY CHAIN.G.Lenaz,M.Degli Espasti and M.Fiugolo.Istituto Botanico,University of Bologna, 40126 Bologna,Italy. The mechanism of superoxide formation in the mitochondrial respiratory chain has been investigated in bovine heart submitochondrial particles and in the isolated bcI complex under different experimental conditions.The use of selective inhibitors of ublquinol-cytochrome c reductase and of succinate-ubiquinone reductase have allowed to discriminate the redox steps where oxygen radicals can be produced.Ubisemiquinone destabllization by such reagents as TTFA,antimycln and DCCD may be responsible for enhanced superoxide formation.The finding is particularly interesting for DCCD,which blocks Hi translocation in the bcl complex without affecting steady state electron transfer actlvlty.The ubiquinone analog DBMIB,which appears to inhibit electron flow in its semiqulnone form at the level of the iron-sulfur proteln,greatly stimulates oxygen consumption in a KCN-insensitive,superoxide dismutase and catalase-sensitive fashion.Thesr studies appear not only to be relevant to the mechanisms by which oxygen radicals are produced in heart mitochondria,but to provide evidence on the redox pathways of the bcl complex.Supported by grants from Minister0 della Pubbllca Istruzione,Roma,Italy.

98 FREE RADICAL DAMAGE OF CARDIAC SARCOPLASMIC RETICULI31 INDUCED BY ARACHIDONIC ACID, Department of Pharmacology, Kanagawa Dental KG2 and H+. E. Okabe, H. Ito, M. Hess. College, Yokosuka, Japan and the Medical College of Virginia, Richmond, VA, USA. Myocardial ischemia is associated with a decrease intracellular pH, sarcoplasmic reticulum (SR) dysfunction and increased production of h-keto PGFl,, but the relationship of PG generation, increasing H+ and SR dysfunction has not been established. In vitro, arachidonic acid (AA, 200 pg/ml) pH 7.0 depressed cardiac SR Ca+2 uptake and ATPase activity (C=O.97 + 0.04, AA=O.48 2 0.07 umoles Caf2/mg-min; C=1.14 + 0.08 AA= 0.59 f 0.12 pmoles Pi/mg-min; p < 0.01). Indomethacin (I; 10 us/ml) inhibited the effects of AA. PGG2 but not PGH2 duplicated the effects of AA; the effect of PGG2 was inhibited by superoxide dismutase (SOD, 10 ug/ml). At pH 6.4, SR calcium uptake was uncoupled from ATP hydrolysis (0.49 + .02 umoles Ca+'/mg-min; 1.12 f .O4 limoles Pi/mgmin) and AA resulted in a further uncoupling (0.24 _+_ .02 umoles Ca '*/rng-min) with no vffect on ATPase activity (p < 0.05). I inhibited the effects of AA. PGC2 but not I'GH? duplicated the effects of AA. SOD did not inhibit the effects of PGG2 but SOD + ZU ti mannitol completely inhibited the effect of PGG?. It is concluded that AA and ~'G(;J at pti 7.0 depress Ca+2 uptake and ATPase activitt by the generation of .Os. IIt pl! Is.4 uncoupling of Ca+* transport from ATP hydrolysis by PGG2 is a result of the gentrntion of the .OH radical. This study incriminates the PG system in the pathogenesis CI~ excitation-contraction uncoupling during the course of myocardial ischemia.

99 FREE RADICAL MECHANISMS OF CYTOTOXIC CARDIAC DAMAGE AND POSSIBILITIES OF THEIR PHARMACOLOGICAL CORRECTION. A.A. Kubatiev, Ja. Mamedov. Central Institute of Doctors' Training, Moscow, USSR. The model of cytotoxic necrosis of rabbit heart was used to show the destructive action of immunoserums on cardiomyocytes. The damage of the cells is a result of inhibition of antioxidative enzyme system with subsequent increase in free radical oxidation of membrane phospholipids. Administration of antioxidants (ubiquinone, Na selenite, OP-6, dibunol and ,&C-tokopherol) blocks the oxidative degradation of phospholipids and prevents tissue necrosis. EPR studies have shown that the drugs used are incorporated into hydrophobic membrane phase and act as traps of free radicals.