[Calcium homeostasis during thymocyte apoptosis. I. Increase in cytosolic Ca2+ concentration at the early stage of apoptosis induced by hydrogen peroxide].

The concentration of free cytosolic Ca2+ ([Ca2+]i), 45Ca2+ entry and the level of reduced glutathione (GSH) after x-irradiation in a dose of 4.5 Gy or 0.1 mM H2O2-treatment were investigated in isolated rat thymocytes during the period preceding electrophoretically detected DNA intranucleosomal fragmentation. Using fura-2 it was shown that the level of [Ca2+]i in X-irradiated thymocytes was not changed as compared with the control, while the GSH content was increased. The gradual increase in [Ca2+]i along with GSH level falling was detected in the H2O2-treated cells. 45Ca2+ entry in the cells exposed to apoptogenic stimuli was not enhanced. After addition of H2O2 to the cells previously treated with thapsigargin further [Ca2+]i increase in both normal and nominally calcium-free medium was detected. Cyclosporine A inhibited Ca2+-mobilizing effect of H2O2, but did not prevent it completely. The role of intracellular calcium depots in calcium homeostasis disturbance during oxidative stress and apoptosis is discussed.