Abstract
Radioadaptive response is a biological defense mechanism that is induced by low-dose ionizing irradiation for cellular resistance to the genotoxic effects of subsequent irradiation. We have reported the effect of pre-irradiation with X-rays of below 10 cGy prior to the challenging irradiation with 3 Gy on the induction of chromosome aberrations in quiescent mouse m5S fibroblasts. Similar effects have been reported by many other groups using various biological end-points, such as cell killing, mutation induction, the induction of micronuclei, and single-cell gel electrophoresis. These results suggest that low dose X-rays is effective for the induction of the radioadaptive response. However, the effect of dose-rate on the induction of the radioadaptive response has been still elusive. We examined the radioadaptive response induced by preirradiation with low dose-rate gamma-rays. When cells were irradiated with 0.8 mGy/min, we observed the adaptive effect with preirradiation of up to 16 cGy. These results suggest that dose-rate is an important factor for the induction of adaptive response. Moreover, we found that the radioadaptive response was suppressed by the down-regulation of protein kinase C alpha. Thus, it was suggested that continuous activation of PKC alpha is important for the induction of the radioadaptive response.
