Effects of X-irradiation on ALP activity and staining of MC3T3-E1 cells. MC3T3-E1 cells were exposed to 0, 0.1, 0.5 and 1.0 Gy of X-irradiation respectively and cells were cultured for 7 days after irradiation. (A) ALP activity was measured and the data were expressed as mean ± SD (n = 3). The ALP activity of 0.5 Gy and 1.0 Gy groups was significantly increased than that of the control group (0 Gy) (*p < 0.05, **p < 0.01). However, 0.1 Gy groups had no significant difference compared with the control. (B) represented plate view of ALP staining. There were more positive cells in 0.5 and 1.0 Gy groups compared with the control.