Two-stage Cell Shrinkage and the OER for Radiation-induced Apoptosis of Rat Thymocytes

Abstract

Suspensions of rat thymocytes were given 0·09—100 Gy using ⁶⁰Co γ-rays. The radiation-induced changes in the thymocytes were examined from minutes to hours postirradiation using electron microscopy, agarose gel electrophoresis, staining and Coulter Counter sizing. Sizing by Coulter Counter showed, for the first time, that thymocytes which undergo apoptosis shrink in two distinct stages, first by a sudden decrease from an original volume of 99 µm³ to a volume of 76 µm³, followed by a gradual decrease to 57 µm³ over the space of a few hours. The oxygen enhancement ratio for apoptosis was measured to be about 3·5, similar to the value for reproductive death for many mammalian cells.