Factors affecting the quantitation of dose-response curves for mutation induction in V 79 Chinese hamster cells after exposure to chemical and physical mutagens

Abstract

Using four common mutagens, ethyl methanesulphonate (EMS), methyl methanesulphonate (MMS), UV, and X-irradiation, the relationship between dose of mutagen, cellular lethality and frequency of 8-azaguanine resistant colonies in V 79 Chinese hamster cells has been examined. Several factors affecting the recovery of mutants including inter and intra-clone metabolic co-operation have been quantitated and their influence on survival response curves examined. Induced mutant frequencies were assayed by two methods in situ, and after replating. After exposure to X-rays, MMS and UV a significantly higher frequency of mutants was observed in replated experiments as compared with the in situ situation, at all survival levels assayed. With EMS, an increment on replating was observed only at high survival levels. The replating data suggest that two types of azg r colonies are produced, i.e. those which contain only azg r cells and those which, due to damage segregation, contain a mixture of azg r and azg s cells. These mixed colonies appear to be lost by metabolic co-operation when mutation frequencies are assayed in situ. The proportion of mixed to homogeneous colonies differs with different mutagens. Taking into account such factors, EMS and UV irradiation were similarly mutagenic at a given survival level, but at equitoxic doses, fewer mutants were recovered after exposure of V 79 cells to MMS and X-rays.