Two forms of potentially lethal damage have similar repair kinetics in plateau- and in log-phase cells

The effect on the survival of X-irradiated Chinese hamster cells (line V79) of two different post-treatments is examined in plateau- and in log-phases of growth. Qualitatively similar results are obtained with cells in both growth phases; that is, similar reductions in survival are effected by post-treatments with hypertonic phosphate buffered saline, and similar increases in survival are effected by post-treatments with conditioned medium. In addition, in both kinds of cells the kinetics of the repair processes are similar even though the kinetics of the two processes differ from each other considerably. While the results indicate that there can be essential differences in the type and/or the pathways of repair of potentially lethal damage, they also illustrate a broader meaning of this term than has been customary. Considered relative to the amount of DNA damage that can be expected to be potentially lethal, it is concluded that the two types of damage that are the subjects of this study represent only small sectors of the total amount of potentially lethal damage.