Inhibition of the UV induction of sister-chromatid exchanges in ICR-2A frog cells by pretreatment with gamma-rays.

Exposure of ICR-2A cells to UV induced the formation of sister-chromatid exchanges (SCEs). However, pretreatment of UV-irradiated cells with gamma-rays resulted in a reduction in the level of SCEs. This effect was observed over a range of UV fluences (1-5 J/m2) and gamma-ray doses (50-500 rad). In addition, the depression of UV-induced SCEs was greatest when the UV treatment was preformed within 3 h after gamma-irradiation. At later times the level of SCEs approached that of cells exposed only to UV.