RELATIONSHIP BETWEEN RADIATION-INDUCED ADAPTIVE RESPONSE IN HUMAN FIBROBLASTS AND CHANGES IN CHROMATIN CONFORMATION

Chromatin conformation changes in the normal human fibroblasts VH-10 w ere studied by the method of anomalous viscosity time dependence (AVTD ). Gamma-irradiation of cells in a dose range of 0.1-3 Gy caused an in crease in maximal viscosity of cell lysates. Conversely, irradiation o f cells with low doses of 0.5 or 2 cGy resulted in a decrease in the A VTD peaks with a maximum effect approximately 40 min after irradiation . The same exposure conditions were used to study a possible adaptive effect of low doses, measured by changes in cell survival. A primary d ose of 2 cGy caused significant modification of cell response to a cha llenge dose. Approximately 20% protection to challenge doses of 0.5 Gy (p < 0.003), 2 Gy (p < 0.02) and 2.5 Gy (p < 0.002) was observed. How ever, the direction of this effect (adaptation or synergism) was found to be dependent on a challenge dose. The combined effect of 2 cGy and 1 Gy was significantly synergistic, while no modification was observe d for 1.5 Gy and 3 Gy. A partial correlation was found between the AVT D changes and cell survival when the combined effect of a primary dose of 2 cGy and challenge dose was examined. The dose of 2 cGy alone inc reased survival by 16% (p < 0.0003). These results suggest that the lo w-dose induced effects on survival may be related to chromatin reorgan ization.