REJOINING AND MISREJOINING OF RADIATION-INDUCED CHROMATIN BREAKS - IV- CHARGED-PARTICLES

We have recently reported the kinetics of chromosome rejoining and exc hange formation in human lymphocytes exposed to gamma rays using the t echniques of fluorescence in situ hybridization (FISH) and premature c hromosome condensation (PCC), In this paper, we have extended previous measurements to cells exposed to charged particles. Our goal was to d etermine differences in chromatin break rejoining and misrejoining aft er exposure to low-and high-linear energy transfer (LET) radiation. Ce lls were irradiated with hydrogen, neon, carbon or iron ions in the LE T range 0.3-140 keV/pm and were incubated at 37 degrees C for various times after exposure. Little difference was observed in the yield of e arly prematurely condensed chromosome breaks for the different ions. T he kinetics of break rejoining was exponential for all ions and had si milar time constants, but the residual level of unrejoined breaks afte r prolonged incubation was higher for high-LET radiation. The kinetics of exchange formation was also similar for the different ions, but th e yield of chromosome interchanges measured soon after exposure was hi gher for high-LET particles, suggesting that a higher fraction of DNA breaks are misrejoined quickly. On the other hand, the rate of formati on of complete exchanges was slightly lower for densely ionizing radia tion. The ratios between the yields of different types of aberrations observed at 10 h postirradiation in prematurely condensed chromosome p reparations were dependent on LET. We found significant differences be tween the yields of aberrations measured in interphase (after repair) and metaphase for densely ionizing radiation. This difference might be caused by prolonged mitotic delay and/or interphase death. Overall, t he results point out significant differences between low-and high-LET radiation far the formation of chromosome aberrations. (C) 1998 by Rad iation Research society.