Chinese hamster ovary cells in monolayer culture, synchronized by mechanically selecting mitotic cells in the absence of drugs, were x-irradiated with 150, 300, or 600 rads at frequent intervals during the cell cycle and examined visually until completion of the first wave of cell division. The synchronized populations consisted of greater than 90% mitotic cells and their subsequent distribution throughout the cycle was carefully documented. At each time-dose combination, growth curves were analyzed for division delay (first, mean, and last cells to divide), the fraction of cells completing the first division, and the duration of the division wave. Results showed that radiation-induced division delay increased exponentially with cell age between early-mid G1 (0.29 minute/rad) and late S-early G2, (0.80 minute/rad) and linearly with dose at any given position in the cell cycle. Mitotic cells were more sensitive than mid- G1 cells (0.43 vs 0.29 minute/rad) and the increase in sensitivity leveled off in G2 at 0.78 minute/rad. Asynchronous populations displayed the same sensitivity as G2 cells. The fraction of cells completing the first division was reduced from about 90% for 150 rads to about 65% for 600 rads, and as for lethality, mitotic cells were most sensitive. The duration of the division waves (4.1-5.4 hours in controls) increased slightly with the greatest increase (2.1 hours) observed in S cells receiving 600 rads.

This content is only available as a PDF.
You do not currently have access to this content.