抄録
Combined effects of methyl methanesulfonate (MMS) and ethyl methanesulfonate (EMS), which were administered successively for each 3 h at different times, or with an interval time of incubation in normal medium for 3 h between treatments with two chemicals were examined on survival and induction of 6TG-resistant and OUA-resistant mutations in Chinese hamster V79 cells.
Pre-treatment with EMS decreased markedly the survival of cells treated with MMS compared with that of cells treated simultaneously with both chemicals. The insertion of interval time between treatments with both chemicals restored the cell survival to that treated with EMS alone. The pre-treatment with MMS also decreased the survival of cells treated with EMS more markedly than that of cells treated with two chemicals simultaneously.
When cells were pre-treated with EMS, the frequency of 6TG-resistant mutations induced by MMS enhanced to be higher than that of cells treated with both chemicals simultaneously. In this case, the restoration effect of incubation time between treatments with two chemicals was found. On the other hand, pre-treatment with MMS, no detectable change in the frequency of 6TG-resistant mutations induced by EMS was found, compared with that in cells treated with both chemicals simultaneously.
In the induction of OUA-resistant mutations induced by EMS, pre-treatment with MMS increased the mutation frequency compared with that in cells treated with both chemicals simultaneously. Also in the simultaneous treatment with both chemicals, the frequency of QUA-resistant mutations was higher than that of mutations induced by EMS alone. The insertion of interval between two treatments with both chemicals reduced the mutation frequency.
