A Transient Change in the Radiosensitivity of Mammalian Cells Resulting from a Change in the Pre-irradiation Culture Conditions

Summary

Mouse Ehrlich ascites cells have been grown in vitro as a monolayer culture (BC cells) and in vivo as ascites tumours developed from I.P. inoculation of cells from an in vitro culture (MC cells). Both BC and MC cells were irradiated and assayed in vitro. The D₀ values for MC cells were always lower than those for BC cells, irrespective of the phase of growth of the tumour. The extrapolation number for MC cells was sometimes higher but never lower than that for BC cells. The fraction of MC cells surviving a fixed dose of irradiation depended on the interval between plating the cells in vitro and irradiation. Survival reached a minimum, usually when this interval was between 4 and 6 hours, and increased again to the constant value measured for BC cells within one or two division cycles. The effect could not be attributed to partial synchronization of the population in the mitotic cycle.