Discrimination of slow growth from non-survival among small colonies of diploid Syrian hamster cells after chromosome damage induced by a range of x-ray doses.

Synchronous samples of cultured diploid Syrian hamster cells (BHK 21 C13/A3) were obtained by mitotic selection, transferred to an observation chamber and given a single X-ray dose in the range 0.2 to 3.8 Gy. Each cell's radiation response was followed by visual observations of its progress alive through post-radiation mitosis (M1), and subsequently of its clonogenicity, by methods already published (Grote et al. 1981 a, b; Joshi et al. 1982a). Our recent paper about the same cell samples (Joshi et al. 1982b) showed that the probability of reaching M1 is nearly unity in controls and over the whole dose range (mean greater than 0.99). The present paper describes the clonogenicity of each sample, based on five daily cell counts at the site of each initial cell. The frequency of viable colonies falls from 98 per cent for unirradiated cells to 8 per cent in the 3.8 Gy sample, but the proportion of these which grow slowly rises from 3 to more than 70 per cent. There was substantial overlap in cell numbers reached by larger abortive colonies and smaller slow-growth colonies, and many of the later had not reached 50 cells at the last count at 5 1/2 days. Impaired colony growth (slow growth or stop growth) was strongly correlated with chromosome fragment loss detected as micronuclei in the daughter cells of M1.