Changes in repair of potentially lethal damage with culture age in EMT6 cells

We have investigated the changes in the amplitude of repair of potentially lethal damage (PLD) in EMT6 cells with increasing culture age and determined the delay necessary to achieve this repair. This experimental system presents all intermediaries between the exponential growth type and a plateau with a cell turnover nearly nil. The radiosensitivity was studied by the colony method. When the percentage of surviving cells was tested immediately after irradiation it was observed that their radiosensitivity increased with culture age. This percentage fell only slightly when the cells were tested for viability 6 hours after irradiation. Therefore, the amplitude of repair increases with culture age. Repair was found to terminate 1, 1.75, 3 and 6 hours after irradiation of cultures aged respectively 2, 4, 6 and 9 days. The delay and the amplitude of repair did not vary significantly for cultures of 9, 11 and 13 days.