OXYGEN‐DEPENDENCE OF NEAR UV (365 NM) LETHALITY AND THE INTERACTION OF NEAR UV AND X‐RAYS IN TWO MAMMALIAN CELL LINES

Abstract

Abstract— The colony‐forming ability of Chinese hamster cells (V‐79) and HeLa cells has been measured after near‐ultraviolet (UV) irradiation, predominantly at 365 nm. To avoid the production of toxic photoproducts, cells were irradiated in an inorganic buffer rather than in tissue culture medium. Under these circumstances near‐UV lethality was strongly oxygen‐dependent. Both cell lines were approximately 10 4 times more sensitive to 254 nm irradiation than to 365 nm radiation when irradiated aerobically. Pretreatment with 6 times 10 5 Jm ‐2 365 nm radiation sensitised the HeLa, but not the V‐79 cell line to subsequent X‐irradiation. Pretreatment of cells with 17 Jm ‐2 254 nm radiation, a dose calculated to produce twenty times more pyrimidine dimers than the 365 nm dose, produced only slight sensitisa‐tion to X‐rays. It is suggested that the sensitisation to X‐rays seen in the HeLa cells after 365 nm treatment is not the result of lesions induced in DNA by the near‐UV radiation, but may reflect the disruption of DNA‐repair systems.