On the Relative Importance of Repair and Progression in Elkind Recovery as Measured in Synchronous HeLa Cells

Abstract

A method is described for the estimation of a quantity which can be considered to be the potential ability to repair sub-lethal damage, or its equivalent, the amount of sub-lethal damage induced. This method was applied to populations of HeLa cells synchronized by mitotic harvest. The sensitivity (with respect to loss of reproductive integrity) of HeLa cells to single radiation doses and the ability to repair significant amounts of sub-lethal damage were found to be dependent on cell-cycle position. The more resistant phases were found to be associated with a greater potential for repair of sub-lethal damage. Significant repair was found to be possible only during early and mid G₁ and in late S. The proportion of sub-lethal damage actually repaired was dependent on the fractionation interval. 4–8 h (⅙–1/3 of cell cycle) allowed only partial repair; 18 h (¾ of cell cycle) sufficed for full repair. 20–25°C incubation was found to permit progression from M into early G₁, but to inhibit totally the repair of sub-lethal damage. Since the amount of sub-lethal damage induced is equivalent to the potential ability to repair sub-lethal damage, it was possible to show that the sub-lethal damage is induced only at certain specific parts of the cell cycle.