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Observations of the First Postirradiation Division of HeLa Cells Following Continuous or Fractionated Exposure to γ Rays

J. B. Mitchell, J. S. Bedford and S. M. Bailey
Radiation Research
Vol. 80, No. 1 (Oct., 1979), pp. 186-197
DOI: 10.2307/3575124
Stable URL: http://www.jstor.org/stable/3575124
Page Count: 12
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Observations of the First Postirradiation Division of HeLa Cells Following Continuous or Fractionated Exposure to γ Rays
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Abstract

The first postirradiation division of synchronized S3 HeLa cells was studied using both continuous and fractionated irradiation treatments. Synchronized HeLa cells continuously irradiated at a dose rate of 37 rad/hr eventually accumulate in mitosis. If the continous irradiation is stopped before the cells enter G2 or even after they have progressed for a limited time into the G2 arrest that develops, very little subsequent accumulation of cells in mitosis occurs. If they progress for a longer time into the G2 arrest, then some mitotic accumulation does occur after the irradiation is stopped. When synchronized cells were allowed to progress through G1 and S before the irradiation was started, very little cell division occurred during subsequent continuous irradiation and extensive mitotic accumulation was observed. Thus, for continous irradiation of HeLa cells, the dose received by a cell during G2 or a G2 delay apparently determines whether it will be able to divide if it reaches mitosis. Arguing against the notion that continuous irradiation during G2 is required to produce a mitotic accumulation was the result of an experiment which showed that a similar effect was obtained using two acute doses: the first to produce a G2 delay and the second to give the necessary dose during the delay. The first dose alone resulted in little mitotic accumulation. The time of delivery of the second dose during the G2 delay affected the extent of mitotic accumulation observed. There was less mitotic accumulation when second acute doses were given early or at intermediate times during the delay than when they were given late during the G2 delay. An accumulation of cells in mitosis was also observed by using a combination of low-dose-rate irradiation to induce a G2 delay, followed immediately by an acute dose of either 500 or 1000 rad. The low-dose-rate treatment alone resulted in no mitotic accumulation.

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