Linear dose —response relationships after prolonged expression times in V-79 Chinese hamster cells

Abstract

The expression time for induced mutants resistant to 6-thioguanine, in V-79 Chinese hamster cells, was determined by respreading the cells in the selective medium, at various times after treatment. The length of the expression time for mutants induced by X-rays, ethyl methane sulphonate nad ultraviolet irradiation was done dependent. For the highest dose used this was 7 to 8 days, beyond which there was no further change in mutant frequency. The dose-response relationship of these agents does not appear to deviate from linearity; this permits the calculation of mutation rate per unit dose. For X-rays this value was 1.35 · 10 −7 per rad per locus, for ethyl methane sulphonate, 2.2 · 10 −2 per mole per locus and for ultraviolet irradiation, 6.3 · 10 −6 per erg per mm 2 per locus. The effectiveness of the 3 different mutagens for the induction of mutations was compared by calculating the increase in mutant frequency per unit of decrease in survival (C 0). These increments in frequency were 5.6 · 10 −5 for X- rays, 69.5 · 10 −5 ethyl methane sulphonate and 16.1 · 10 −5 for ultraviolet irradiation.