A Study on Recovery from Potentially Lethal Damage induced by gamma-Irradiation in Plateau-phase Vero Cells in vitro

Kim, Il Han; Choi, Eun Kyung; Ha, Sung Whan; Park, Charn Il; Cha, Chang Yong

Abstract

Recovery from potentially lethal damage (PLDR) after irradiation was studied in plateau-phase culture of Vero cells in vitro. Unfed plateau-phase cells were irradiated with dose of 1 to 9 gy using Cs-137 irradiator. Cells then were incubated again and left in situ for 0, 1, 2, 3, 4, 5, 6 and 24 hours and then were trypsinized, explanted, and subcultured in fresh RPMI-1640 media containing 0.33% agar. Cell survival was measured by colony forming ability. An adequate number of heavily irradiated Vero cells were added as feeder cells to make the total cell number constant in every culture dish. As the postirradiation in situ incubation time increased, surviving fraction increased saturation level at 2 to 4 hours after in situ incubation. As the radiation dose increased, the rate of PLDR also increased. In analysis of cell survival curve fitted to the linear-quadratic model, the linear inactivation coefficient (alpha) decreased largely and reached nearly to zero but the quadratic inactivation coefficient (beta) increased minimally by increment of postirradiation in situ incubation time. So PLDR mainly affected the damage expressed as alpha. In the multitarget model, significant change was not obtained in D0 but in Dq. Therefore, shoulder region in cell survival curve was mainly affected by PLDR and terminal slope was not influenced at all. And dose-modifying factor by PLDR was relatively higher in shoulder region, that is, in low dose area below 3 gy.