The fate of U.V.-induced lesions affecting SCEs,chromosome abberrations and survival of CHO cells arrested by deprivation of arginine

CHO cells undergo proliferative arrest when incubated in medium deficient in the amino acid arginine (ADM). Cells arrested in this way can be released and resume mitotic activity after a brief lag period. The incidence of U.V.-induced sister chromatid exchanges (SCEs) induced in cells arrested in ADM was reduced when the cells were incubated in ADM after irradiation and prior to release. Periods of incubation in ADM of 24 and 48 h prior to release reduced the resulting SCE levels (relative to the SCE levels present in cells irradiated immediately prior to release) by an average of 35 and 45% respectively. A similar time-dependent decrease in the incidence of chromosome aberrations induced in CHO cells arrested in ADM was not observed. Despite the decrease in SCEs over time in ADM, the survival of ADM-arrested cells was not enhanced by a period of incubation in ADM after irradiation of 48 h. These observations are consistent with the hypothesis that the U.V.-induced lesions responsible for the induction of SCE are repaired in time in ADM-arrested CHO cells. Repair of those lesions resulting in chromosome aberrations was not detected in ADM-arrested CHO cells. This absence of repair of certain lesions was apparently reflected in the absence of any enhancement of cell survival.