Cell Killing and Division Delay in Asynchronous and Synchronized HeLa Cells Irradiated with Alpha Particles or X Rays

Abstract

HeLa cells irradiated with a single or 2 split doses of .alpha. particles or X-rays were observed with time-lapse photography or examined for their colony-forming ability. The cell cycle-dependent variation of cell killing and division delay were compared in synchronous and asynchronous cell populations. Cellular damage by .alpha. particles was manifested in the form of cessation of division, or death, rather than partial division which was predominant for X irradiation. Furthermore, an increased number of interrupted divisions leading to death following split doses correlated with the lack of production of reparable damage from .alpha. particles. As to the cell cycle-dependent variation of radiosensitivity, a somewhat different pattern was noted with .alpha. particles, especially for division delay. The pattern of cell killing with .alpha. particles was similar to that found with X-rays, in that high sensitivity was noted at or close to mitosis, while a resistant peak remained at late S, but not in early G1. The pattern of division delay was similar for X-rays and .alpha. particles during G2-M, with a maximum delay at mid G2 and no delay past the transition point, but differed during G1-S. During this period, division delay increased with cell age, whereas it showed a broad peak at G1-S boundary and a trough at late S for X-rays. There was a reverse correlation between division delay and cell killing except for G2-M in the case of X-rays. However, such was not the case for .alpha. particles.