Abstract
§Introduction§ Biological effects by low dose rate irradiation is known to be different from those by high dose rate irradiation. Specific cellular (NIH/PG13Luc cells) responses and gene expression pattern for low dose rate irradiations have been detected by us. In present study, we observed focus formation of γH2AX and p53BP1 in murine NIH/PG13Luc cells.
§Materials and Methods§High dose rate irradiations (0.5 Gy/min) were performed by soft-X ray for 2, 4, 8, 16 min. Low dose rate irradiations (0.1 mGy/h ∼ 90 mGy/h) for 1 or 2 days were used by γ-simulator (137Cs γ-source: 1.1Tbq, 110Gbq) in IES. The irradiated murine NIH/PG13 cells were fixed by 4% parahormaldehyde immediately after irradiation, and reacted with 1st antibody (anti-γH2AX or anti-p53BP1). Alexa 488 or Alexa 647 conjugated Anti IgG were used for immunocytochemical analysis. The number and size of foci were used In Cell Analyzer (GE Healthcare).
§Results and Disucussions§ Numbers of γH2AX and p53BP1 foci were increased depending on total dose and dose rate in middle dose rate irradiations (more than 9 mGy/h). On the other hand, in low dose rate irradiations (less than 1.5 mGy/h), their focus formation were independent on total dose and dose rate, which was shown like reverse dose rate effect. These results indicate that DNA repair in low dose rate irradiations less than 1.5 mGy/h have a totally different molecular mechanism from that in middle and high dose rate irradiations. (This work was supported by Aomori Prefecture, Japan.)
