ON THE ROLE OF INTRACELLULAR CONCENTRATION OF CA2+ AND H+ IN THYMOCYTE DEATH AFTER IRRADIATION

The role of intracellular Ca2+ and H+ concentrations in radiation-indu ced interphase death of rat thymocytes has been studied. In response t o concanavalin A treatment in the Ca2+-containing medium, or to the Ca Cl2 treatment in the Ca2+-free medium, the [Ca2+]i rise in irradiated cells was as in the non-treated cells. No changes in the level of [Ca2 +]i and pH(i) were found within 1 h after irradiation of thymocytes wi th a dose of 6 Gy. 15 muM 5-(N-ethyl-N-isopropyl)-amiloride, an inhibi tor of Na+/H+ exchange, did not affect the DNA fragmentation. The frag mentation was prevented by 2-4 muM ,4-dichlorophenyl)-methoxy]-ethyl)- 1-H-imidazolium chloride, an inhibitor of calmodulin. The above data i ndicate that triggering of interphase death in irradiated thymocytes i s not mediated by changes in either [Ca2+]i or pH(i). Such changes see m to be involved in intermediate steps of the interphase death process .