An increase in the Ca2+ permeability of the plasma membrane caused by the radiation-induced thymocyte apopthosis

Parameters of the Ca2+-permeability (the 45Ca influx rate in the presence of orthovanadate blocking the Ca2+-APThase, and the initial rate of the 45Ca uptake) and the DNA fragmentation were determined in rat thymocytes after γ-irradiation-induced (with a dose of 5 Gy) apopthosis. It is shown that modification of the membrane Ca2+ permeability in the irradiated thymocytes precedes a stage of initiation of the DNA degradation. A decrease of disturbance of the membrane passive permeability increases as the thymocyte apopthosis progresses. The obtained data suggest that disturbance of the passive Ca2+ permeability and the intracellular Ca2+ homeostasis are responsible for the apopthosis of lethally irradiated thymocytes. 28 refs., 3 figs