Radiation Response of Mammalian Cells Grown in Culture: I. Repair of X-Ray Damage in Surviving Chinese Hamster Cells

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Abstract
The generally observed threshold type of response of the lethal effect of X-rays on cultured mammalian cells means that damage must be accumulated before a lethal response is produced. Surviving cells are, therefore, damaged cells. A study was undertaken, using two cell lines of the Chinese hamster propagated in vitro, to determine whether or not sublethal damage is heritable as might be expected if lethal damage is primarily genie. Using 55-kv X-rays, glass-attached cells, and colony formation as a criterion of survival, we found that: (1) the cell lines studied displayed mean lethal doses close to those found with other mammalian cell lines (100 to 150 rads); (2) in contrast to other mammalian cell lines, the extrapolation or "hitness" numbers observed were somewhat larger (5 to 10); (3) surviving cells rapidly repaired their sublethal damage which appeared to be completed before their first postirradiation division; and (4) the system(s) responsible for recovery in surviving cells was not attenuated by repeated exposures. The results are discussed in connection with the question of the primary sites of action of X-rays in mammalian cells and the relevance of cellular recovery to radiation therapy.