Superoxide Disrnutase Does Protect the Cdtured Rat Cardiac Myocytes Against Hypoxia/Reoxygenation Injury

The effect of superoxide dismutase (SOD) on membrane integrity and fluidity of the cultured neonatal rat cardiac myocytes in vitro was investigated under the condition of hypoxia and hypoxia/reoxygenation. Lactate dehydrogenase (LDH) concentration was used as the biochemical indicator for the loss of cell membrane integrity. Fluorescence polarization (FP), average microviscosity (N) and anisotropy (Ast), which are inversely proportional to the fluidity of cell membrane, were assayed. Cells were respectively exposed to hypoxia or hypoxia/reoxygenation for different periods of time in the absence or presence of SOD at various concentrations. Hypoxia alone or hypoxia/ reoxygenation brought injury to the cultured myocytes. This was demonstrated by changes in LDH and membrane fluidity. In the former LDH concentration gradually increased in a time-dependent manner and the values of FP, N and Asf were significantly increased. The changes in membrane integrity and fluidity induced by hypoxia or hypoxia/reoxygenation could be prevented by adding SOD to the culture medium. The results provide a direct evidence that SOD (740 u.ml^-1, the effective dose) was effective in protecting cultured myocytes against the injury as well as an indirect evidence of free radical generation. Based on the results obtained from this study and the establishment of concept of optimally effective dose by Bernier and Omar et al, it was suggested that some previous reports, in which no evidence was found both in protective effect of SOD and in free radical generation by using only one dose in hypoxia/reoxygenation model, should be interpreted with caution.