Abstract
Phosphorylated ataxia telangiectasia mutated forms foci (p-ATM foci) shows the initial DNA damage, such as DNA double strand breaks, by radiation. In this study, we analyzed the dose-response relationship for the number of p-ATM foci in MRC-5 cells that irradiated of X-rays with doses ranging for ~200 mGy and indicated that the number of p-ATM foci showed a supralinear dose-response relationship. However, this dose-response relationship was not observed in cells treated with lindane that is an inhibitor of bystander effects. Moreover, the number of p-ATM foci obtained by subtracting the number of p-ATM foci in lindane-treated cells from the number of p-ATM foci in untreated cells was proportional to the dose at low doses ~10 mGy. Thus, the increase in the number of p-ATM foci in the range of ~10 mGy was largely due to bystander effects.
It is well known that the radioadaptive response is important biological effect of low dose radiation. We investigated whether the bystander effect related to the induction of the radioadaptive response. Conditioning irradiation of the MRC-5 cells with ~10 mGy resulted in a significant protective effect against the occurrence of p-ATM foci induced by a challenging dose of 200 mGy. However, this phenomenon was inhibited by lindane. This result indicated that the radioadaptive response was induced in dose region where bystander effect has occurred. The findings of our present study provide a direct evidence of relationship between the bystander effect and the radioadaptive response.
