Observations of the First Postirradiation Division of HeLa Cells Following Continuous or Fractionated Exposure to γ Rays

Abstract

The first postirradiation division of synchronized S3 HeLa cells was studied using both continuous and fractionated irradiation treatments. Synchronized HeLa cells continuously irradiated at a dose rate of 37 rad/hr eventually accumulate in mitosis. If the continous irradiation is stopped before the cells enter G2 or even after they have progressed for a limited time into the G2 arrest that develops, very little subsequent accumulation of cells in mitosis occurs. If they progress for a longer time into the G2 arrest, then some mitotic accumulation does occur after the irradiation is stopped. When synchronized cells were allowed to progress through G1 and S before the irradiation was started, very little cell division occurred during subsequent continuous irradiation and extensive mitotic accumulation was observed. Thus, for continous irradiation of HeLa cells, the dose received by a cell during G2 or a G2 delay apparently determines whether it will be able to divide if it reaches mitosis. Arguing against ...