Abstract
We have been studying the biological effects of low-dose radiation using a synchrotron X-ray microbeam irradiation apparatus developed in KEK-PF. This system is able to provide an X-ray microbeam of arbitrary size larger than 5 microns square. In this research, by using this advantage, we have compared the survival fractions of V79 cells irradiated with X-ray microbeams of different sizes. We have already reported that low-dose hypersensitivity was observed in nucleus-irradiation with a 10 microns square X-ray beam more clearly than in broad-field irradiation. In order to elucidate the contribution from irradiated cytoplasm, we irradiated the whole cell with a 50 microns square X-ray beam and compared the survival fractions with those obtained in irradiation only to nucleus. The survival curve obtained in 50 microns square X-ray beam irradiation is almost the same as that obtained in broad-field irradiation. At the low-dose region, the low-dose hypersensitivity, which was clearly observed when only cell nucleus was irradiated with X-ray beam, became less observable. Considering the situation that in 50 microns square X-ray beam irradiation, the entire cytoplasm, as well as the nucleus, was irradiated uniformly with X-rays, while the cytoplasm was not irradiated in 10 microns square X-ray beam irradiation, these results suggest that the energy deposition in cytoplasm might induce some kind of intracellular signaling and enhance the repair activity of the cell, and hence the low-dose hypersensitivity might be suppressed in whole cell irradiation.
