Rapid Recovery in Plateau-Phase Mammalian Cells

Rapid split-dose and rapid single-dose recovery was examined in two rodent cell lines in culture: hamster lung fibroblasts (V-79) and contact-inhibited mouse embryo fibroblasts (10T1/2). Cell turnover in density-inhibited plateau-phase 10T1/2 cell cultures is very low as compared with V-79 cells. Plateau cultures were exposed to cobalt-60 ..gamma.. rays at 85 to 90 rad/sec; 0 to 90 min of incubation at 37/sup 0/C was allowed either between two exposures or following a single exposure before subculture at low density. A rapid phase of recovery occurred in plateau-phase 10T1/2 cell cultures occurring within 4 to 10 min after irradiation, whereas little recovery occurred during this time in the V-79 cell line. Rapid recovery was not observed in either cell line following irradiation during exponential growth. When plateau-phase 10T1/2 cells were irradiated with a total dose of 1100 rad given as two 550-rad doses with exposures separated by 10 min, survival was enhanced by a factor of 5 over that seen following a single 1100-rad dose. When 10 min was allowed to elapse after a single dose before subculture, a twofold enhancement in survival occurred. This rapid recovery appeared to result from an additive effect of split-dose and potentially lethal damage repair.more » When rapid split-dose recovery had occurred, however, little further enhancement in survival took place when cells were placed under conditions which favored recovery of additional potentially lethal damage.« less