Figure 1.

Cellular radioadaptive response is very sensitive to environmental oxygen concentration. (a) Human fibroblasts were cultured under conventional condition (20–21% O₂). For assessing the effect of 0.1Gy on 4.0 Gy-induced DNA damage, cells were pretreated with a dose of 0.1 Gy or sham treated, after 12 h, followed by a 0 or 4.0 Gy treatment. The cells were harvested 1 h after the 4 Gy treatment and subjected to immunostaining with γH2AX (red) and DAPI (blue). (b) Quantification of γH2AX-positive cells shown in a. Bars represent mean±S.D. of (∼100 cells per sample) three independent experiments. *<0.05, **<0.01. (c). Human fibroblasts were maintained at 5% O₂ for at least 12 h before being irradiated and analyzed as described in a. (d) Quantitative analysis of γH2AX-positive cells shown in c was carried out as in b. (e) Human fibroblasts were pretreated with or without 10 mM NAC for 1 h. The cells were either sham or 0.1 Gy irradiated and harvested 1 h after for immunostaining with carboxy-H2DCFDA (#C400, Invitrogen/Molecular probes, green) and DAPI (blue). (f) Fibroblasts were treated with 10 mM NAC (+NAC) for 1 h and then subjected to the treatment and analysis as in a. (g) Quantitative analysis of γH2AX-positive cells shown in f was carried out as in b