Abstract:
:Chinese hamster ovary cells were exposed to various heat treatments followed by X-irradiation, and the induction and repair of DNA strand breaks was studied using the alkaline unwinding technique. Heat treatments alone were found to cause DNA strand breakage only for temperatures greater than or equal to 43 degrees C, whereas the number of radiation-induced strand breaks was unaffected by additional heating. Strand break repair was studied for irradiated cells preheated at temperatures ranging from 42 degrees C to 45 degrees C. The total repair curve could be separated into three phases, a fast (t = 0-15 min), an intermediate (t = 15-120 min) and a slow (t greater than or equal to 120 min) phase. All phases were altered when cells were heated either prior to or after irradiation. The fast and the intermediate phase could be well interpreted by the assumption that irradiation leads to both primary and secondary single-strand breaks, the latter being generated by enzymatic incision at sites of damaged bases. For irradiation alone, the ratio of all secondary strand breaks to all primary breaks was fsec = 1.5 +/- 0.5. This ratio was not altered by preceding heat treatments (mean fsec = 1.7 +/- 0.2). The main effect of heating on the repair kinetics of single-strand breaks was an increase in the repair half-time of primary and secondary breaks (maximum increase by a factor of 3.4), whereas the generation of secondary breaks was only slightly retarded (factor 1.3). The slow repair phase, which is assumed to represent the repair of DNA double-strand breaks, was best described by a single exponential component. The half-time of this component was found to increase from tau slow = 170 +/- 70 min for non-heated cells to tau slow = 345 +/- 80 min for cells heated at 45 degrees C for 20 min, indicating that heat inhibited the repair of double-strand breaks. For irradiation alone, the initial fraction of the slow component was fslow = 0.065 +/- 0.004. This fraction was enhanced by additional heating, with a maximum increase by a factor of 2.7 for cells heated at 45 degrees C for 20 min. This elevation cannot be the result of an enhanced induction of double-strand breaks, but must be associated with an additional formation of slowly repaired strand breaks during repair incubation. These additional strand breaks must arise from strand breaks which in non-heated cells are repaired during the fast or intermediate phase.(ABSTRACT TRUNCATED AT 400 WORDS)
journal_name
Int J Radiat Bioljournal_title
International journal of radiation biologyauthors
Dikomey E,Franzke Jdoi
10.1080/09553009214550851subject
Has Abstractpub_date
1992-02-01 00:00:00pages
221-33issue
2eissn
0955-3002issn
1362-3095pii
8NL5EK41HEHP0316journal_volume
61pub_type
杂志文章abstract:PURPOSE:MRL-lpr/lpr mice, a model for various autoimmune diseases, were repeatedly irradiated with 0.5 Gy of gamma-rays, and changes in their autoimmune manifestations were investigated. MATERIALS AND METHODS:MRL-lpr/lpr mice at 13 weeks of age were maintained in plastic cages and exposed whole-body to 0.5 Gy gamma-ra...
journal_title:International journal of radiation biology
pub_type: 杂志文章
doi:10.1080/09553000500519790
更新日期:2005-10-01 00:00:00
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journal_title:International journal of radiation biology
pub_type: 杂志文章
doi:10.1080/09553009514550791
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更新日期:2010-02-01 00:00:00
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更新日期:2011-07-01 00:00:00
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journal_title:International journal of radiation biology
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更新日期:1994-11-01 00:00:00
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更新日期:1990-08-01 00:00:00
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journal_title:International journal of radiation biology
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doi:
更新日期:1994-12-01 00:00:00
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更新日期:1995-04-01 00:00:00
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更新日期:1996-05-01 00:00:00
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更新日期:2011-02-01 00:00:00
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更新日期:1991-01-01 00:00:00
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更新日期:1996-11-01 00:00:00
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journal_title:International journal of radiation biology
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更新日期:1991-02-01 00:00:00
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pub_type: 杂志文章,评审
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更新日期:2011-02-01 00:00:00