NATURE OF THE CARDIOMYOCYTE INJURY-INDUCED BY LIPID HYDROPEROXIDES

Objective: As a result of oxidative stress to membrane lipid matrix, t he peroxidation of polyunsaturated fatty acids induced the transient f ormation of lipid hydroperoxides (ROOH). The aim of this study was to evaluate the damaging effects of ROOH on the cardiac cell and the link between the alterations observed and intracellular calcium overload. Methods: Necrosis of cultured rat cardiac cells was determined by meas uring the release of lactate dehydrogenase (LDH). In guinea-pig papill ary muscles, action potential (A9) and isometric tension were recorded with standard microelectrodes and a transducer, respectively. The rea ctive oxygen species (ROS) scavenging properties of tested compounds w ere determined using a cell-free model of lipid photoperoxidation. Res ults: 15(S)-HpETE (15(S)-hydroperoxyeicosatetraenoic acid), an arachid onic acid hydroperoxide, induced a concentration-dependent loss of car diomyocytes membrane integrity. The release of LDH induced by 15(S)-Hp ETE(30 mu M) was prevented by a ROS scavenger, BW755C (10 mu M), but n ot by a sarcolemmal calcium channel blocker, Amlodipine (10 mu M), or a calcium overload protective agent, R56865 (10 mu M). Cardiomyocytes necrosis induced by calcium paradox was prevented by Amlodipine(10 mu M) and R56865 (10 mu M), but not by BW755C (10 mu M). Superfusion of p apillary muscles with 15(S)-HpETE (20 mu M) induced a membrane depolar ization and a marked reduction in the AP amplitude and duration. Conco mitantly, a transient positive inotropic effect and a progressive rise in diastolic tension were observed. These alterations were maximal af ter 15 min and associated with delayed after-depolarizations (DADs) an d after-contractions. Every alteration was inhibited by BW755C (10 mu M) and R56865 (30 mu M), but not by Amlodipine (1 mu M). Ryanodine (1 mu M), a blocker of sarcoplasmic reticulum calcium channel, only preve nted the appearance of DADs and after-contractions. Only BW755C exibit ed ROS scavenging properties. Conclusions: ROOH induced enzyme leakage and electromechanical alterations in cardiac cells. These effects of ROOH implicated oxidative mechanisms and resulted in an intracellular calcium overload.