2-STAGE CELL SHRINKAGE AND THE OER FOR RADIATION-INDUCED APOPTOSIS OFRAT THYMOCYTES

Suspensions of rat thymocytes were given 0.09-100 Gy using Co-60 gamma -rays. The radiation-induced changes in the thymocytes were examined f rom minutes to hours post-irradiation using electron microscopy, agaro se gel electrophoresis, staining and Coulter Counter sizing. Sizing by Coulter Counter showed, for the first time, that thymocytes which und ergo apoptosis shrink in two distinct stages, first by a sudden decrea se from an original volume of 99 mum3 to a volume of 76 mum3, followed by a gradual decrease to 57 mum3 over the space of a few hours. The o xygen enhancement ratio for apoptosis was measured to be about 3.5, si milar to the value for reproductive death for many mammalian cells.