Effects of X Irradiation on Cell Kinetics in Cultured Rat Tooth Germ Cells.

体外培养大鼠切牙牙胚，建立上皮样细胞。体外培养的大鼠牙胚细胞（RTG-2）和小鼠成纤维细胞系（L-5）分别接受2、5和10戈伊的X射线照射。用流式细胞仪检测细胞DNA含量，并与DNA直方图比较。各剂量组异步L细胞照射后均出现<G_2>+M期细胞聚集（<G_2>阻滞）。2戈伊照射后20 h内细胞直方图恢复到未照射时的直方图。当细胞暴露于10戈伊时，即使在<G_2>照射后30小时，细胞积累到+M期也持续存在。同步化M期细胞照射后，细胞进入S期受阻，期内<G_1>聚集（<G_1>阻滞）现象消失. RTG-2细胞生长缓慢，倍增时间约为70小时。RTG-2的DNA直方图显示，S<G_1>期和<G_2>+M期所占比例分别为66%、28%和6%。RTG-2细胞经2戈伊X射线照射后，出现S期细胞聚集现象，表明S期<G_1>细胞进入S期受阻或受阻<G_2>。上述结果提示L细胞和慢增殖的RTG-2细胞对X射线的敏感性可能存在不同的机制。

Tooth germ of rat incisor was cultured in vitro and the epithel like cells were established. Cultured rat tooth germ cells ( RTG-2 ) and mouse fibroblastic cell lin ( L-5 cells ) were exposed to 2, 5 and 10 Gy of X-rays. The cellular DNA contents were measured by a flow cytometry and the effect of X irradiation was compared with the DNA histograms.The results were as follows,1. In every dose group of asynchronous L cells, cell accumulation of <G_2> +M phases ( <G_2> block ) occured after irradiation. The histogram pattern of cells exposed to 2 Gy returned to the unirradiated one within 20 hours after irradiation. When the cells were exposed 10 Gy, cell accumulation into <G_2> +M phases persisted even at 30 hours after irradiation. After irradiation to synchronized cells in M phase, the cells were prevented from entering in S phase and the accumulation in <G_1> phase ( <G_1> block ) was observed.2. RTG-2 cells showed slow growth and the doubling time was about 70 hours. DNA histogram of RTG-2 showed that the proportion of <G_1> , S and <G_2> +M phases were 66, 28 and 6%, respectively. When the RTG-2 cells were irradiated with 2 Gy of X-rays, cell accumulation in S phase was occured, indicating the <G_1> block and/or prevention of S phase from entering <G_2> phase. These results suggested the possibility of different mechanism between L-cells and slow proliferating RTG-2 cells as to the sensitivity to X irradiation.