Radiosensitivity and repair of radiation damage in human HF19 fibroblasts

Survival curves of HF 19 fibroblasts exhibit a continuous curvature, whether the cells are irradiated in exponential growth phase or in plateau phase and whether plating occurs immediately after irradiation or is delayed. The quadratic model is well suited for the fitting and the comparison of the curves obtained under different conditions. At the survival level of 10(-4), the split-dose method leads to the demonstration of the repair of sublethal damage by growing cells. By combining the split-dose method with delayed plating, we could demonstrate that plateau phase cells repair both sub-lethal as well as potentially lethal damage to a great extent. The parameters of the survival curve of fibroblasts irradiated in plateau phase and plated 24 hours later are similar to those of a large number of mammalian cell lines. When the results are fitted with the quadratic model, it is seen that delayed plating of plateau phase cells results in a proportional reduction of the parameters alpha and beta, suggesting that repair involves the damage corresponding to the two mechanisms described by the quadratic model and affects them to the same extent.