Comparison of F ratios generated from interphase and metaphase chromosome damage induced by high doses of low- and high-LET radiation.
Although biophysical models predict a difference in the ratio of interchromosomal to intrachromosomal interarm exchanges (F ratio) for low- and high-LET radiations, few experimental data support this prediction. However, the F ratios in experiments to date have been generated using data on chromosome aberrations in samples collected at the first postirradiation mitosis, which may not be indicative of the aberrations formed in interphase after exposure to high-LET radiations. In the present study, we exposed human lymphocytes in vitro to 2 and 5 Gy of gamma rays and 3 Gy of 1 GeV/nucleon iron ions (LET = 140 keV/micrometer), stimulated the cells to grow with phytohemagglutinin (PHA), and collected the condensed chromosomes after 48 h of incubation using both chemically induced premature chromosome condensation (PCC) and the conventional metaphase techniques. The PCC technique used here condenses chromosomes mostly in the G(2) phase of the cell cycle. The F ratio was calculated using data on asymmetrical chromosome aberrations in both the PCC and metaphase samples. It was found that the F ratios were similar for the samples irradiated with low- and high-LET radiation and collected at metaphase. However, for irradiated samples assayed by PCC, the F ratio was found to be 8.2 +/- 2.0 for 5 Gy gamma rays and 5.2 +/- 0.9 for 3 Gy iron ions. The distribution of the aberrations indicated that, in the PCC samples irradiated with iron ions, most of the centric rings occurred in spreads containing five or more asymmetrical aberrations. These heavily damaged cells, which were either less likely to reach mitosis or may reach mitosis at a later time, were responsible for the difference in the F ratios generated from interphase and metaphase analysis after exposure to iron ions.
Wu
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Radiation Biophysics Laboratory, NASA Johnson Space Center, Houston, Texas 77058 and Kelsey-Seybold Clinic, NASA Johnson Space Center, Houston, Texas 77058, USA.
George
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K
Willingham
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V
Kawata
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T
Cucinotta
F A
FA
D002869:Chromosome Aberrations; D002877:Chromosomes, Human / Q000187:drug effects / Q000528:radiation effects*; D004307:Dose-Response Relationship, Radiation; D016195:G2 Phase / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D018499:Linear Energy Transfer; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000528:radiation effects / Q000648:ultrastructure; D008297:Male; D008387:Marine Toxins; D008677:Metaphase / Q000187:drug effects / Q000235:genetics* / Q000528:radiation effects; D010080:Oxazoles / Q000494:pharmacology
D008387:Marine Toxins; D010080:Oxazoles; C059041:calyculin A