Fixation of Potentially Lethal Radiation Damage by Post-irradiation Exposure of Chinese Hamster Cells to 0·5 M or 1·5 M NaCl Solutions

Summary

The effect of 0·05 M and 1·5 M NaCl treatments on CHO cells during and after irradiation has been examined. Treatment with either hypotonic or hypertonic salt solutions during and after irradiation resulted in the fixation of radiation damage which would otherwise not be expressed. The half time for fixation was 4 to 5 min, and the increased expression of the potentially lethal damage by anisotonic solutions was mainly characterized by large decreases in the shoulder of the survival curve, as well as by decreases in D₀. Fixation of radiation damage at 37°C occurred to a much greater extent for the hypertonic treatment than for the hypotonic treatment and was greater at 37°C than at 20°C. Although both the hypotonic and hypertonic treatments during and after irradiation reduced or eliminated the repair of sublethal and potentially lethal damage, treatment during irradiation only, radiosensitized the cells when the treatment was hypotonic, and radioprotected the cells when the treatment was hypertonic. These observations are discussed in relation to salt treatments and different temperatures altering competition between repair and fixation of potentially lethal lesions, the number of which depends on the particular salt treatment at the time of irradiation.