THE EFFECT OF POSTIRRADIATION HOLDING AT 22-DEGREES-C ON THE REPAIR OF SUBLETHAL, POTENTIALLY LETHAL AND POTENTIALLY NEOPLASTIC TRANSFORMING DAMAGE IN GAMMA-IRRADIATED HELA X SKIN FIBROBLAST HUMAN HYBRID-CELLS

The effect of postirradiation holding at 22 degrees C on cell growth, progression of cells through the cell cycle, and the repair of subleth al, potentially lethal and potentially neoplastic transforming damage in gamma-irradiated HeLa x skin fibroblast human hybrid cells has been examined. Cell growth and cell cycle progression were essentially sto pped at this reduced temperature. Cell survival was dramatically reduc ed by holding confluent cultures for 6 h at 22 degrees C, as opposed t o 37 degrees C, after 7.5 Gy gamma radiation delivered at a rate of 2 Gy/min. Return of the cells to 37 degrees C for 6 h after holding at 2 2 degrees C did not result in increased survival. A similar effect was obtained when the cells were held at 22 degrees C between split-dose irradiation of log-phase cultures where no increase in survival was ob served over a split-dose interval of 4 h. In this case a partial incre ase in survival was observed upon returning the cells to 37 degrees C for 3 h after holding at 22 degrees C for the first 3 h of the split-d ose interval. Neoplastic transformation frequency was not enhanced by holding confluent cultures for 6 h at 22 degrees C after 7.5 Gy gamma radiation. This is consistent with previous observations that misrepai r of potentially neoplastic transforming damage already occurs at 37 d egrees C. The overall results are interpreted in terms of the reduced temperature favoring misrepair, rather than inhibition of repair, of s ublethal, potentially lethal and potentially transforming radiation da mage.