Irradiation with He-Ne laser can influence the cytotoxic response of He-La cells to ionizing radiation

A monolayer of HeLa cells in plateau-phase of growth was exposed to He-Ne laser radiation (632.8 nm, 100 J/m(2)) either 5 min, 60 min or 180 min before gamma-irradiation (0.2 to 10 Gy, 6.75 Gy/min). It has been shown that in the case of a 5-min interval between the mio types of irradiations the survival curve was practically identical to the survival curve of the cells after gamma-irradiation only. In the case of He-Ne laser exposure 60 min before gamma-irradiation with doses of over 5 Gy, a fraction of more resistant cells was revealed: their Do was twice as high as the Do of the main population (3.6 and 1.7 Gy, respectively). A preexposure of cells to He-Ne laser (100 J/m(2)) 60 or 180;min before gamma-irradiation (5 Gy) also changed the shape of the growth curves as compared to gamma-irradiated cells (stimulation in exponential phase of growth). It is proposed that the preexposure of cells to He-Ne laser radiation activates, in a subpopulation of cells, processes which speed up the repair of gamma-radiation damage. The possibility that the described phenomenon is an adaptive response of cells is discussed.