The Effect of X-Irradiation on HeLa during Different Phases of the Growth Cycle

Abstract

Monolayers of the established HeLa strain were exposed to various doses of x radiation during different phases of the growth cycle. The effects as measured by changes in cell and clone number were dependent on the radiation dose. Four days after irradiation was the optimum day for assessing irradiation damage in this system. Significant variations in the radiation sensitivity of HeLa during different stages of the growth cycle were observed by both assessing procedures. Cells in the logarithmic growth phase were most sensitive to radiation, followed in order by cells in the negative growth acceleration, stationary, and latent phases of the population cycle. The ranges of these differences were greater by cell than by clone count methode. The closest correlation between the two techniques was observed when radiation was administered during the logarithmic phase of growth. It is hoped that these studies may eventually facilitate the development of a satisfactory assay system for measuring the in vitro radiation sensitivity of short-term monolayer cultures of tumors, as well as the long-term monolayer cultures of established cell strains. (auth)