Chromosomal analysis of Chinese hamster V79 cells exposed to multiple gamma-ray fractions: induction of adaptive response to mitomycin C.

Chinese hamster V79 cells were irradiated daily with 0.3 Gy of gamma-rays 5 times per week for 12 weeks (total 18 Gy). These cells were challenged with an additional dose of 15. Gy gamma-rays or treated with 5 micrograms/ml of mitomycin C (MMC) for 2 h. In spite of the high total accumulated dose of gamma-rays, the number of chromosomal aberrations and sister-chromatid exchanges (SCEs) did not significantly increase in the preirradiated cells, as compared to control cells. If preirradiated cells were challenged with an additional 1.5 Gy of gamma-rays, an insignificant decrease in the yield of chromatid aberrations was observed. In contrast, preirradiated cells became significantly more resistant to the induction of chromosomal damage when challenged with mitomycin C. Our results suggest that multiple fractions of gamma-rays can induce the adaptive response to mitomycin C in preirradiated cells.