Unique mode of cell death in freshly isolated adult rat ventricular cardiomyocytes exposed to hydrogen peroxide

To address whether adult rat ventricular cardiomyocytes (ARVCs) exposed to oxidant stress die via apoptosis (secondarily by necrosis) or primarily by necrosis, we exposed ARVCs to hydrogen peroxide (H 2 O 2 ; 0.1–100 μM) for up to 24 h and then compared them with isoproterenol-induced apoptotic and Triton X-induced necrotic controls. Cellular shrinkage preceded plasma membrane disruption, reflected by trypan blue uptake in ARVCs exposed to lower concentrations of H 2 O 2 (1 μM; a necrotic pattern). DNA fragmentation, caspase-3 activation, mitochondrial membrane potential preservation, and ATP preservation were all apparent in ARVCs treated with low H 2 O 2 (0.5 μM), but not in those treated with high H 2 O 2 (10 μM). In addition, electron microscopy revealed unique morphology in H 2 O 2 -treated ARVCs; i.e., the nuclei had a homogeneous ground glass-like appearance that was never accompanied by chromatin condensation. Apparently, high concentrations of H 2 O 2 caused primary necrosis in ARVCs, whereas low concentrations induced biochemically comparable apoptosis, although the latter did not satisfy the morphological criteria of apoptosis. These findings caution against the use of oxidant stress, H 2 O 2 in particular, as an inducer of apoptosis in ARVCs.