The influence of multiple mutagenic treatments on the occurrence of 6-thioguanine-resistant mutants in dividing V79 cells.

Repeated treatments of dividing Chinese hamster V79 cells with ultraviolet radiation or a simple monofunctional alkylating agent (methyl methanesulphonate, N-methyl-N'-nitro-N-nitrosoguanidine or N-methyl-N-nitrosourea) were studied with regard to the pattern of cumulative increase of 6-thioguanine-resistant mutants in the surviving population. There were 5-10 divisions of surviving cells between two successive treatments. Repeated treatments with different agents produced different effects. The observed results indicating either a higher or lower than additive effect of single doses may be explained by induced repair processes.