Analyses of Differential Sensitivities of Synchronized HeLa S 3 Cells to Radiations and Chemical Carcinogen during the Cell Cycle: 1. Establishment of optimum conditions for obtaining a large highly purified synchronized population

In the present study, we have established the optimum conditions for a combination of colcemid (0.025 μg/ml for 6 hours) and harvesting techniques in order to obtain a large highly purified population of mitotic HeLa S 3 cells. This method does not cause any visible biological or cytological damage to cells. The mitotic phase and the late G1 to the early S phase of HeLa S 3 cells synchronized by this method were found to be more sensitive to X-irradiation of 400 R than were the other phases in the cell cycle. Sensitivity to UV-irradiation of 100 ergs/mm2 increased late in the G1 phase, reached a maximum in the middle of the S phase, and decreased through the remainder of the S and G2 phases. In addition, the mitotic phase was as sensitive to UV-irradiation as the middle of the S phase. On the other hand, sensitivity to 4-NQO-treatment with 5 × 10-9M for 20 minutes decreased from the late S to the early G2 phase. All other phases were relatively sensitive to 4-NQO. These findings may indicate that the effects of X-, UV-irradiation and 4-NQO on HeLa S 3 cells differ qualitatively from each other.