抄録
Human diploid cells were treated with ethyl methanesulfonate (EMS) and cultured in selection medium containing 8-azaguanine (8AG) to induce mutation to 8AG-resistance. The effects of factors such as the inoculum size and the mutation expression time on the induced mutation frequency of cells were examined. When cells were treated with 10-2M EMS for 2 hours and selected with 10μg/ml of 8AG, the induced mutation frequency was highest on inoculation of 2.5×105 cells, although this frequency was not significant statistically. When EMS-treated cells were selected with 30μg/ml of 8AG, the highest induced mutation frequency was obtained on inoculation of 105 cells. The mutation frequency was higher when 105 cells treated with EMS were cultured in normal medium for 48 hours (mutation expression time) before selection with 8AG, than in cultures with longer or shorter mutation expression times. This mutation expression time of 48 hours corresponds to the time during which about half the cell population treated with EMS divides once. Microscopic examination on the numbers of cells in colonies indicated that human diploid cells treated with or without EMS do not all grow exponentially but that in some cases after each cell division only one daughter cell continued to divide.
