Persistent increase in the rates of apoptosis and dicentric chromosomes in surviving V79 cells after X-irradiation

In parallel to delayed reproductive death and delayed micronuclei in surviving V79 cells that have been reported, the frequency of apoptosis and dicentrics was investigated in the same cell line, 1-2 weeks after X-ray doses between 1 and 12 Gy. Apoptosis was assessed by morphological criteria after staining with Giemsa and using the Apoptag(TM) method in parallel. The frequency of apoptosis peaked 48 h after irradiation at about 35% as a function of dose and then decreased to about 10% on day 3. It remained 10 times higher than in unirradiated cells until day 14. The frequency of dicentric chromosomes 24 h after irradiation increased according; to a linear-quadratic function, up to about 110% after 12 Gy, decreased 3 days later to about 10% and remained about 5-fold higher than in control cells. The dose-response relationship was similar for all the various end-points of expression of radiation induced genomic instability, showing a steep increase of the frequency with dose up to 3-4 Gy and with no further increase at higher radiation doses.