A new method to study activated oxygen species induced damage in cardiomyocytes and protection by Ca2+-antagonists

It has been proposed that oxygen derived free radicals contribute to reperfusion injury in ischemic tissue: radical induced lipid peroxidation is believed to cause membrane destruction, eventually evolving to cell death. A method is introduced which investigates the effect of exogenously generated reactive O2 species on isolated Ca2+-tolerant rat cardiomyocytes. Singlet oxygen (O2(1)), generated by photo-excitation of the photosensitive dye rose bengal, induced the transformation of elongated rod-shaped cells into hypercontracted rounded cardiomyocytes. These shape changes were prevented by removal of extracellular Ca2+ or by addition of radical scavengers. Pre-treatment with various classes of Ca2+-antagonists dose-dependently reduced the number of hypercontracted cardiomyocytes after exposure to O2(1). Compounds not active on the slow Ca2+-channel (e.g. flunarizine-like) provided a better degree of protection than the genuine slow Ca2+-channel blockers (e.g. dihydropyridines). Ultrastructurally, cardiomyocytes exposed to O2(1) showed a loss of cytochemically demonstrable sarcolemma-associated Ca2+ and the presence of clustered Ca2+-deposits in the mitochondria. Drug pre-treated cells displayed a Ca2+-distribution pattern comparable to unchallenged control cells.