Plateau-phase human dermal fibroblasts and whole blood G0 lymphocytes obtained from the same three healthy donors were irradiated with different doses of 200 kV X rays. The genomic yields of dicentrics were evaluated in the first postirradiation mitosis. Fluorescence in situ hybridization was used to "paint" the chosen whole chromosomes. The yields of reciprocal translocations were scored for all donors for chromosome 4, and also for the third donor for chromosomes 7 and 9. The amounts of reciprocal translocations were scored in the first as well as in later (4th or 5th) postirradiation cell divisions. The yields of dicentrics involving the painted chromosomes were scored for one donor as well. The yields of dicentrics observed in the lymphocytes and in the skin fibroblasts from the same individual were significantly different. Yields of dicentrics were much lower in fibroblasts than in lymphocytes. This was observed for all doses up to 4 Gy for all three donors studied. Fibroblasts from two individuals were also irradiated with 6 Gy. The interindividual variability was similar in both cell types. The yields of reciprocal translocations in lymphocytes and in fibroblasts were similar. The yields of reciprocal translocations were practically constant when comparing the first mitotic divisions and later divisions. The observed ratio of translocations:dicentrics was higher in fibroblasts than in lymphocytes, where it was about 1 for one donor and about 2 for the other two donors. Significant differences between the yields of dicentrics and translocations as well as between the shapes of their dose responses were observed in lymphocytes and fibroblasts from the same individual. Our experimental data suggest that repair processes with different efficiencies or different repair processes might be active in cells of different types of tissue.

Chromosomes in primary tumour cells derived from a squamous cell carcinoma of the gingival mucosa were analysed. The ploidy of individual chromosomes and the frequencies of reciprocal translocations in unirradiated and irradiated cells were assessed by the method of fluorescence in situ hybridization. Hybridization probes for whole chromosomes 1, 2, 3, 4, 9 and 12 were used. The analysis was carried out in early (1st-3rd) passage cells and for comparison, in late (25th-30th) passage cells. A radiation-induced polyploidy of all analysed chromosomes was observed in irradiated (D = 4 Gy) early as well as late passage cells, with the exception of chromosome 4 in late passage cells. Ploidy of chromosomes 1 and 4 was studied at lower doses (1-3 Gy), too. Polyploidy was observed for doses >2 Gy. Some of the analysed chromosomes showed a high 'spontaneous' translocation frequency in both types of cells. The frequencies of radiation-induced translocations were similar in early and late cells and these frequencies were not always proportional to the length of the chromosomes studied. The radiosensitivity of individual chromosomes was not correlated with the level of spontaneous translocation frequency.

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