Analysis of Ar-ion and X-ray-induced chromatin breakage and repair in V79 plateau-phase cells by the premature chromosome condensation technique.
OBJECTIVE
The premature chromosome condensation technique has been used to compare chromatin breakage and repair in noncycling V79 cells following high and low LET radiation.


METHODS
Plateau-phase V79 cells were exposed to graded doses of low energy Ar ions (LET 1233 keV/microm) and X-rays. Cells were fused to mitotic V79 cells immediately after exposure to examine initial chromatin breakage or after various time intervals of post-irradiation incubation to investigate the kinetics of chromatin break rejoining as well as the fraction of unrejoined fragments.


CONCLUSIONS
For both radiation qualities an average initial number of about 2.4 excess PCC fragments per cell per Gy was found increasing linearly with dose. The distributions of PCC chromosomes plus excess fragments among cells followed Poisson statistics after X-ray irradiation, while an overdispersion of the frequencies was observed after Ar-irradiation indicating that a single particle traversal through a cell nucleus can produce multiple chromatin lesions. Moreover, for both radiation types the rejoining of excess fragments has been examined. Both data sets could be fitted well to first-order kinetics with a single component. Despite similar rates of 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 induced excess fragments remained unrejoined, only 14% of X-ray-induced lesions were not rejoined. Furthermore, comparison of the residual number of excess PCC fragments with recently published data on the yield of chromosome aberrations in first post-irradiation metaphases shows that for both radiation types more aberrations are detected in interphase than in metaphase cells. 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.
Nasonova
E
E
Biophysik, Gesellschaft für Schwerionenforschung, Darmstadt, Germany.
Gudowska-Nowak
E
E
Ritter
S
S
Kraft
G
G
D000818:Animals; D001128:Argon / Q000009:adverse effects*; D002460:Cell Line; D002467:Cell Nucleus / Q000528:radiation effects; D002843:Chromatin / Q000528:radiation effects*; D002875:Chromosomes / Q000528:radiation effects*; D006224:Cricetinae; D004307:Dose-Response Relationship, Radiation; D007477:Ions; D007700:Kinetics; D008938:Mitosis / Q000528:radiation effects; D015233:Models, Statistical; D013997:Time Factors; D014965:X-Rays / Q000009:adverse effects*
D002843:Chromatin; D007477:Ions; D001128:Argon