Radiation-induced transformation of 10T 1/2 mouse cells in the plateau phase: post-irradiation changes and serum dependence.

The frequency of transformation induced in plateau phase 10T 1/2 cells by a single dose of X-rays decreased as a function of time during the early post-irradiation period (0 approximately 6 hr), and then tended to increase during the late post-irradiation period (7 approximately 48 hr). The extent of reduction, as measured in terms of the ratio (6 hr/0 hr value) of transformation, ranged from 0.2 to 1.1, depending upon the batch of serum which was used for pre-irradiation culture. The above findings, together with the results of a serum-free experiment, suggested that a factor affecting such reduction is present in sera. Transformation frequency depended not only on the serum used for pre-irradiation culture but also on the serum for assay culture. To maintain internal consistence of results from a series of experiments, the use of a single batch of serum is essential.