Studies on in vitro carcinogenesis. I. Autoradiographic and biochemical study on the incorporation of labelled methylcholantrene into mouse embryonic cells.

The incorporation of radioactive labelled Methylcholanthrene into CBA/T6T6 mouse embryonic fibroblast cultures was studied by using light and electronmicroscopic autoradiographic and also liquid scintillation counting techniques. During 24 hrs treatment time at the applied Methylcholanthrene concentrations (0.01-2.5 mug/ml) the proportion of cells labelled with 3H-Methylcholanthrene and the number of grains above the cells showed a relationship with the duration of treatment and also with the doses. Up to 24 hrs all cells were labelled after treatment with 2.5 mug/ml whereas at 0.01 and at 0.1 mug/ml concentrations Methylcholanthrene could have been detected only 2 and 10% of the cell population resp. The presented results suggested that labelling index reached saturation level earlier than the average number of grains. Electronmicroscopic autoradiography revealed a rather even distribution of grains and there were no signs for preferential binding site of Methylcholanthrene. Biochemical separation showed that 59 and 44% of the radioactivity was bound to macromolecules at 1 and 24 hrs after commencing treatment resp.