Cell survival and recovery processes in Chinese hamster AA8 cells and in two radiosensitive clones

Cell survival and recovery after gamma irradiation were investigated in a Chinese hamster ovary cell line (AA8) and in two radiosensitive clones (EM9 and NM2) derived from it. When analyzed by the multitarget and linear-quadratic equations, the dose-response curves for survival of both EM9 and NM2 cells, compared with AA8 cells, were characterized by a decreased magnitude of the shoulder or single-hit region (as reflected by Dq or alpha, respectively) but no difference in the terminal slope or double-hit region (as reflected by DO or beta, respectively). Recovery from sublethal damage (SLD) and potentially lethal damage (PLD) was measured in the three cell lines to examine the relationship between the shoulder width of the survival curve and the magnitude of cellular recovery. NM2 cells exhibited a reduced shoulder on their survival curve and a reduced capacity for SLD recovery, compared with AA8 cells, after equitoxic doses of radiation. EM9 cells, which also had a reduced shoulder on their survival curve, displayed the same rate and extent of recovery as AA8 cells for both SLD and PLD. PLD recovery, as assayed in fed plateau-phase NM2 cells by delayed plating, occurred with slower initial kinetics but to the same final extent as that in AA8 cells, resulting in modification of both the shoulder and the slope of the survival curve. However, PLD recovery, as assayed in log-phase NM2 cells by postirradiation treatment with hypertonic salt, was normal and affected predominantly the slope of the survival curve. These data demonstrate that although both SLD and PLD recovery play a role in determining cell survival, cell-survival curve parameters may not always be useful in predicting cellular recovery capacity.