Rapid split dose and single dose recovery were examined in exponentially growing and in density inhibited, stationary phase culture of human diploid fibroblasts. The cultures were exposed to cobalt-60 gamma rays at a dose-rate of 50 rad/s:0-90 min were allowed between exposures or following a single exposure prior to subculture at low density. A rapid phase of recovery occurred which was of greater magnitude in the plateau phase cultures. Dose-dependent rapid recovery occurred within 2-10 min of the initial exposure, and was greater following single dose versus split dose irradiations. When the post-irradiation temperature was maintained at 37 degrees C, two phases of recovery were observed, one at early times (2-10 min) and one later (30-90 min). No recovery was observed with incubation at 4 degrees C, whereas incubation at room temperature (25 degrees C) allowed rapid recovery (2-10 min) to take place, but not the slower process (30-90 min). The hypothesis that this rapid recovery phenomenon is related to cell-to-cell contact and to repair of potentially lethal damage is discussed.
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Malcolm et al. (1980) studied this question.