title: Number of Fe ion traversals through a cell nucleus for mammalian cell inactivation near the bragg peak.
abstract: HeLa and CHO-K1 cells were irradiated with Fe ions (1.14 MeV/nucleon) near the Bragg peak to determine how many ion traversals through a cell nucleus are necessary to induce cell inactivation. The ion traversals through a cell nucleus were visualized by immunostaining the phosphorylated histone H2AX (gamma-H2AX), as an indicator of DNA double strand breaks (DSBs), to confirm that DSBs are actually induced along every Fe ion traversal through the nucleus. The survival curves after irradiation with Fe ions decreased exponentially with the ion fluence without a shoulder. The inactivation cross sections calculated from the slope of the survival curves and the standard errors were 96.9 +/- 1.8 and 57.9 +/- 5.4 microm2 for HeLa and CHO-K1 cells, respectively, corresponding to 0.442 and 0.456 of the mean value of each cell nucleus area. Taking the distribution of the cell nucleus area into consideration with an equation proposed by Goodhead et al. (1980), which calculates the average number of lesions per single ion track through the average area of a sensitive organelle (mainly nucleus), these two ratios were converted to 0.705 and 0.659 for HeLa and CHO-K1 cells, respectively. These ratios were less than one, suggesting that the average numbers of lethal hits per cell produced by a single ion traversal were less than one. We thus considered two possible explanations for ion traversals of more than one, necessary for cell inactivation.
authors.affiliation: Department of Life Science, Rikkyo University, Japan. tkonishi@lir.rikkyo.ne.jp
authors.forename: Teruaki
authors.initials: T
authors.lastname: Konishi
authors.forename: Akihiro
authors.initials: A
authors.lastname: Takeyasu
authors.forename: Nakahiro
authors.initials: N
authors.lastname: Yasuda
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Natsume
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Nakajima
authors.forename: Kenichi
authors.initials: K
authors.lastname: Matsumoto
authors.forename: Taku
authors.initials: T
authors.lastname: Asuka
authors.forename: Yukio
authors.initials: Y
authors.lastname: Sato
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Furusawa
authors.forename: Kotaro
authors.initials: K
authors.lastname: Hieda
mesh_terms: D000818:Animals; D016466:CHO Cells; D002467:Cell Nucleus / Q000502:physiology* / Q000528:radiation effects*; D002470:Cell Survival / Q000528:radiation effects*; D006224:Cricetinae; D003412:Cricetulus; D004307:Dose-Response Relationship, Radiation; D006367:HeLa Cells; D006801:Humans; D007504:Iron Radioisotopes; D018499:Linear Energy Transfer / Q000502:physiology*; D011829:Radiation Dosage; D011874:Radiometry / Q000379:methods*
chemical_list: D007504:Iron Radioisotopes