In order to study how reproductive death is related to interphase death and to characterize biochemical changes associated with interphase death, mouse leukemic L5178Y cells in suspension culture were irradiated with large doses (6-200 kR) of x-rays. Eosin staining-the criterion used for detection of dead or dying cells-increased around the time of increased leakage of <tex-math>${}^{3}{\rm H}\text{-}{\rm RNA},{}^{3}{\rm H}\text{-proteins}$</tex-math> and <tex-math>${}^{3}{\rm H}\text{-}{\rm DNA}$</tex-math> from the cells, indicating that the eosin staining represents damage of cell membranes. Interphase death of cultured L5178Y cells was characterized by dose-dependent S-shaped curve of eosin staining, while reproductive death showed a somewhat dose-independent two-step curve (6). Judging from 50% eosin-staining time, the transition from reproductive death to interphase death is abrupt, suggesting a possible difference between the two types of killing mechanisms. From studies of the effects of various metabolic inhibitors on development of interphase death, we speculate that radiation-induced disorganization of the cells may be the cause of interphase death of rapidly dividing L5178Y cells in culture.

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