The influence of ionization density on the DNA synthetic phase and survival of irradiated mammalian cells.

Depression of the DNA synthetic rate of exponentially growing V79 cells was transient with a dose-dependent maximum at 1 hour after exposure to sparsely or densely ionizing radiation. The dose-effect curves were biphasic for 241Am alpha-particles as well as for 60Co gamma-rays, being partly congruent if inhibition of DNA synthesis was expressed per S-phase cell. The lesions responsible caused a prolongation of the DNA synthetic period (S-phase) after sparsely ionizing X- or 60Co gamma-rays. However, no such effect was observed during the first 4 hours after exposure to densely ionizing alpha particles, peak pions and high LET neon ions. The effect was dose-rate independent. The inhibition of the DNA synthetic rate seems to be only partly related to survival.