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。培养的大鼠牙胚细胞(RTG-2)和小鼠成纤维细胞系(L-5细胞)分别接受2、5和10GyX射线照射。结果如下：1.照射后各剂量组的L细胞均出现细胞积聚现象，出现细胞周期阻滞现象。照射后20h内，2Gy射线照射的细胞直方图恢复到未照射的水平。当细胞受到10Gy射线照射时，即使在照射后30h，细胞仍聚集在~lt；G_2&Gt；+M期。结论：1.照射M期同步化细胞后，阻止细胞进入S期，并观察到细胞在G_1、G_1、Gt；期的积聚。RTG-2细胞生长缓慢，倍增时间约为70h。RtG-2DNA直方图显示&lt；G_1&gt；、S和&lt；G_2&gt；+M期的比例分别为66%、28%和6%。2GyX射线照射后，细胞聚集于S期，说明S期被阻断和/或阻止进入G_2期。这些结果提示，L细胞和缓慢增殖的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.