Calcium ionophore-induced egg activation and apoptosis are associated with the generation of intracellular hydrogen peroxide

The present study was designed to investigate whether calcium ionophore-induced activation and apoptosis are associated with the generation of hydrogen peroxide (H2O2) in rat eggs cultured in vitro. Culture of metaphase-II (M-II) arrested eggs in Ca2+/Mg2+-deficient medium did not induce egg activation, while a second polar body was observed in 20% of eggs when cultured in Ca2+/Mg2+-supplemented medium. In Ca2+/Mg2+-deficient medium, lower concentrations of calcium ionophore (0.2,0.4 and 0.8 mu m) not only induced egg activation in a dose-dependent manner but also generation of intracellular H2O2 (84.40 +/- 0.50 ng/egg) when compared to control eggs (80.46 +/- 1.34 ng/egg). The higher concentration of calcium ionophore (1.6 mu m) induced apoptosis and pronounced generation of intracellular H2O2 (92.43 +/- 0.93 ng/egg) in treated eggs. Conversely, cell-permeant antioxidant such as 2(3)-tert-butyl-4-hydroxyanisole (BHA) reduced intracellular H2O2 level (81.20 +/- 1.42 ng/egg) and protected against calcium ionophore-induced morphological changes characteristics of egg activation and apoptosis. These results clearly suggest that calcium ionophore-induced activation and apoptosis are associated with the generation of intracellular H2O2 in rat eggs.