Effect of Dose Rate on Cell Killing and DNA Strand Break Repair in CHO Cells Exposed to Internal β-rays from Incorporated [3H]thymidine

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Abstract
Survival as well as repair of DNA strand breaks were studied in CHO cells after exposure to internal β-rays from incorporated [3H]thymidine at 4°C (equivalent to an exposure at ‘infinitely high’ dose rate) and at 37°C (low dose rate). DNA strand breaks were determined by the alkaline unwinding technique. In cells exposed at 4°C cell killing was five times higher (D0 = 250 decays per cell) than in cells exposed at 37°C (D0 = 1280 decays per cell). Strand breaks induced by 3H decay at 37°C were repaired with the same kinetics as those generated at 4°C. Therefore the different degrees of cell killing at 4°C and 37°C cannot be attributed to a difference in the repair kinetics for DNA strand breaks.