SURVIVAL AND MUTATION OF CHINESE-HAMSTER CELLS AFTER ULTRAVIOLET-IRRADIATION AND CAFFEINE TREATMENT

UV-irradiated Chinese hamster cells [V79] on post-irradiation treatment with caffeine in growth medium for 24 h gave rise to biphasic UV-survival curves. At caffeine concentrations between 0.001 and 0.1 mM, control and caffeine-grown cells had similar survival curves initially from 0 to 30 J/m2. At fluences > 30 J/m2, there was effectively only little further killing of caffeine-grown cells beyond that observed at 30 J/m2. At concentrations of caffeine > 0.5 mM, there was a gradual sensitization in the early part of the survival curve with increasing caffeine concentrations, but at fluences > 30 J/m2, the slopes in the survival curves decreased considerably. The initial sensitization observed at low UV fluences is possibly due to the suppression of post-replication repair by caffeine. After high fluences of UV exposures in these excision-deficient cells, in the presence of caffeine, the possibility of an induced SOS-like repair process was suggested. Caffeine increased the yield of UV-induced 8-azaguanine-resistant mutants only for the cell population exposed to UV fluences > 30 J/M2, supporting this suggestion.