IRRADIATION WITH HE-NE-LASER CAN INFLUENCE THE CYTOTOXIC RESPONSE OF HELA-CELLS TO IONIZING-RADIATION

A monolayer of HeLa cells in plateau-phase of growth was exposed to He-Ne laser radiation (632.8nm, 100J/m(2)) either 5, 60 or 180min before gamma-irradiation (0.2-10Gy, 6.75Gy/min). In the case of a 5min interval between the two 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 >5Gy, a fraction of more resistant cells was revealed: their D-o was twice as high as the D-o of the main population (3.6 and 1.7 Gy, respectively). A preexposure of cells to He-Ne laser (100J/m(2)) 60 or 180min before gamma-irradiation (5Gy) also changed the shape of the growth curves as compared with 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.