title: Hyperfast, early cell response to ionizing radiation.
abstract: OBJECTIVE
  To determine whether the oscillatory changes of radio-sensitivity which occur within fractions of a second to a few minutes following flash irradiation correlate with an altered incidence of apoptosis, DNA strand breaks or lipid-coupled signalling.
  
  
  METHODS
  Human tumor cells (SQ-20B, LoVo) or Chinese hamster V79 fibroblasts were exposed to split-dose, pulse irradiation with 3.5 MeV electrons at high dose-rate (12 or 120 Gy x s(-1)) and the effects assessed by clonogenic assays, analysis of DNA cleavage and microscopic observation.
  
  
  RESULTS
  The processes underlying oscillatory radiation response were saturable, but did not correlate with an increased incidence of DNA single- or double-strand breaks or apoptosis. N-acetylcysteine and inhibitors of lipid-derived signalling also failed to alter oscillatory response. However, this response did correlate with phenotypic alterations evoking mitotic or delayed cell death. Furthermore, high dose-rate irradiation provided a lower level of instability than protracted gamma-ray irradiation.
  
  
  CONCLUSIONS
  It is proposed that the early steps of DNA damage recognition and repair following priming radiation exposure bring about rapid, synchronous remodeling of chromatin, evoking enhanced chromosome damage upon re-irradiation.
authors.affiliation: Unité 350 INSERM, Institut Curie-Biologie, Orsay, France.
authors.forename: V
authors.initials: V
authors.lastname: Ponette
authors.forename: C
authors.initials: C
authors.lastname: Le Péchoux
authors.forename: E
authors.initials: E
authors.lastname: Deniaud-Alexandre
authors.forename: M
authors.initials: M
authors.lastname: Fernet
authors.forename: N
authors.initials: N
authors.lastname: Giocanti
authors.forename: H
authors.initials: H
authors.lastname: Tourbez
authors.forename: V
authors.initials: V
authors.lastname: Favaudon
mesh_terms: D000818:Animals; D017209:Apoptosis / Q000528:radiation effects*; D002460:Cell Line; D002469:Cell Separation; D006224:Cricetinae; D004247:DNA / Q000528:radiation effects*; D004249:DNA Damage / Q000528:radiation effects; D053938:DNA Fragmentation / Q000528:radiation effects; D004307:Dose-Response Relationship, Radiation; D005347:Fibroblasts / Q000528:radiation effects; D005434:Flow Cytometry; D005720:Gamma Rays; D006801:Humans; D020287:In Situ Nick-End Labeling; D050356:Lipid Metabolism; D008938:Mitosis / Q000528:radiation effects; D018384:Oxidative Stress / Q000528:radiation effects; D015398:Signal Transduction / Q000528:radiation effects; D013997:Time Factors; D014407:Tumor Cells, Cultured
chemical_list: D004247:DNA