Repair of Sublethal and Potentially Lethal X-Ray Damage in Synchronous Chinese Hamster Cells

Abstract

Mitotic cells were selected from asynchronous cultures and X-irradiated either in mitosis, G1, or S phase. Repair of sublethal damage was measured by the increase in survival which occurred as two doses of radiation were separated by incubation at 37 or 20°C. Repair of potentially lethal damage was measured by the increase in survival which occurred as the cells were held at 20°C after a single dose. The maximum amount of repair of sublethal damage during S phase increased with dose (the dose modifying factor, DMF, increased from 1.05 or 1.14 for 500 rads to 1.11 or 1.20 for 1000 rads for treatment at 20 or 37°C, respectively), but did not result in the survival expected if all of the sublethal damage had been repaired. The rate of repair (T1/2 of 15-20 min) was the same at either 20 or 37°C and was independent of dose. The rate of repair of potentially lethal damage during S phase was the same as that for repair of sublethal damage, but the magnitude of repair of potentially lethal damage (DMF of 1.08 in...