Rapid Recovery in Human Diploid Fibroblasts

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Abstract
Rapid split dose and single dose recovery were examined in exponentially growing and in density inhibited, stationary phase cultures of human diploid fibroblasts. The cultures were exposed to 60Co .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 vs. split dose irradiations. When the post-irradiation temperature was maintained at 37.degree. C, 2 phases of recovery were observed: rapid recovery occurred at an early time (2-10 min) and a slower process occurred later (30-90 min). No recovery was observed with incubation at 4.degree. C. Incubation at room temperature (25.degree. C) allowed rapid recovery (2-10 min) to take place, but not the slower process (30-90 min). Rapid recovery phenomenon apparently is related to cell-to-cell contact and repair of potentially lethal damage.