Rapid recovery in human diploid fibroblasts.

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.