Radiation Response of Mammalian Cells Grown in Culture. II. Survival and Recovery Characteristics of Several Subcultures of HeLa S3 Cells After X Irradiation

Abstract

Three subcultures of HeLa S3 cells, which are of human origin, were studied to determine their response to X rays. The ability of the cells to retain unlimited proliferation was determined by standard tissue-culture techniques for handling single cells. Cells were irradiated with 55 kv X rays delivered at 722 rad per minute. The three subcultures showed characteristic differences in their survival parameters. Two of the subcultures had average mean lethal doses (MLD) near 100 rad, while the third had an average MLD of 131 rad. A range of average extrapolation numbers from 1.4 to 4.9 was observed, and each subculture had a different but characteristic average value. The three subcultures also contained different chromosome complements. It was not possible to correlate either the MLD or the extrapolation number with chromosome complements. In spite of this, surviving cells of all three subcultures were capable of repairing sublethal damage starting immediately after X irradiation. Repeated recovery cycles were also demonstrable when sufficient lengths of time were allowed between doses. In addition to recovery, increases in the MLD of recovered cells in some instances caused the net survival obtained after a given total dose of X rays to be considerably greater when the same total dose was fractionated.