Cultured mouse SR-1 cells exposed to low dose of {gamma}-rays become less susceptible to the induction of mutagenesis by radiation as well as bleomycin

The effect of pre-exposure of cultured mouse SR-1 cells to alow dose of -rays on the induction of mutations at the hprtlocus by subsequent high dose radiation or bleomycin was studied.When cells were pre-exposed to 0.01 Gy -rays, the inductionof mutations by a 3 Gy -ray dose given 18 or 24 h later wassignificantly reduced as compared with those which did not receivethe low dose pre-exposure. When cells were challenged with 5or 10 µg/ml bleomycin for 12 h, which can produce double-strandbreaks in DNA, instead of 3 Gy -rays, a similar mutageneticadaptive response was observed. We conclude that this resistanceto radiation- or bleomycininduced mutation is attributed tothe induction of a DNA double-strand break repair mechanism.