Analysis of Ar-ion and X-ray-induced chromatin breakage and repair in V79 plateau-phase cells by the premature chromosome condensation technique

Purpose: The premature chromosome condensation technique has been used to c ompare chromatin breakage and repair in noncycling V79 cells following high and low LET radiation. Materials and methods: Plateau-phase V79 cells were exposed to graded doses of low energy Ar ions (LET 1233 keV/mum) and X-rays. Cells were fused to m itotic V79 cells immediately after exposure to examine initial chromatin br eakage or after various time intervals of post-irradiation incubation to in vestigate the kinetics of chromatin break rejoining as well as the fraction of unrejoined fragments. Results and conclusions: For both radiation qualities an average initial nu mber of about 2.4 excess PCC fragments per cell per Gy was found increasing linearly with dose. The distributions of PCC chromosomes plus excess fragm ents among cells followed Poisson statistics after X-ray irradiation, while an overdispersion of the frequencies was observed after Ar-irradiation ind icating that a single particle traversal through a cell nucleus can produce multiple chromatin lesions. Moreover, for both radiation types the rejoini ng of excess fragments has been examined. Both data sets could be fitted we ll to first-order kinetics with a single component. Despite similar rates o f rejoining cellular repair was noticeably less effective for Ar ions than for X-rays. While after 10 h of post-irradiation incubation 60% of Ar ion i nduced excess fragments remained unrejoined, only 14% of X-ray-induced lesi ons were not rejoined. Furthermore, comparison of the residual number of ex cess PCC fragments with recently published data on the yield of chromosome aberrations in first postirradiation metaphases shows that for both radiati on types more aberrations are detected in interphase than in metaphase cell s. Yet, for comparable doses this difference is more pronounced for Ar ions indicating that scoring of high LET induced aberrations in metaphase cells might result in a significant underestimation of the produced damage.