Synchronous suspensions of the radiosensitive S/S variant of the L5178Y murine leukaemic lymphoblast at different positions in the cell cycle were exposed aerobically to segments of heavy-ion beams (20Ne, 28Si, 40Ar, 56Fe and 93Nb) in the Bragg plateau regions of energy deposition. The incident energies of the ion beams were in the range of 460 ± 95 MeV u-1, and the calculated values of linear energy transfer (LET∞) for the primary nuclei in the irradiated samples were 33 ± 3, 60 ± 3, 95 ± 5, 213 ± 21 and 478 ± 36 keV μm-1, respectively; 280 kVp X-rays were used as the baseline radiation. Generally, the maxima or inflections in relations between relative biological effectiveness (RBE) and LET∞ were dependent upon the cycle position at which the cells were irradiated. Certain of those relations were influenced by post-irradiation hypothermia. Irradiation in the cell cycle at mid-G1 to mid-G1 + 3 h, henceforth called G1 to G1 + 3 h, resulted in survival curves that were close approximations to simple exponential functions. As the LET∞ was increased, the RBE did not exceed 1.0, and by 478 keV μm-1 it had fallen to 0.39. Although similar behaviour has been reported for inactivation of proteins and certain viruses by ionizing radiations, so far the response of the S/S variant is unique for mammalian cells. The slope of the survival curve for X-photons (D0: 0.27 Gy) is reduced in G1 to G1 + 3 h by post-irradiation incubation at hypothermic temperatures and reaches a minimum (D0: 0.51 Gy) at 25°C. As the LET∞ was increased, however, the extent of hypothermic recovery was reduced progressively and essentially was eliminated at 478 keV μm-1. At the cycle position where the peak of radioresistance to X-photons occurs for S/S cells, G1 + 8 h, increases in LET∞ elicited only small increases in RBE (at 10% survival), until a maximum was reached around 200 keV μm-1. At 478 keV μm-1, what little remained of the variation in response through the cell cycle could be attributed to secondary radiations (δ rays) and smaller nuclei produced by fragmentation of the primary ions.
|Original language||English (US)|
|Number of pages||16|
|Journal||Proceedings of the Royal Society B: Biological Sciences|
|Publication status||Published - 1989|
ASJC Scopus subject areas
- Agricultural and Biological Sciences(all)
- Agricultural and Biological Sciences (miscellaneous)
Responses of synchronous L5178Y S/S cells to heavy ions and their significance for radiobiological theory. / Lett, J. T.; Cox, A. B.; Story, M. D.; Ehmann, U. K.; Blakely, E. A.In: Proceedings of the Royal Society B: Biological Sciences, Vol. 237, No. 1286, 1989, p. 27-42.
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