CLASTOGENIC EFFECTS OF DEFINED NUMBERS OF 3.2 MEV ALPHA-PARTICLES ON INDIVIDUAL CHO-K1 CELLS

Research to determine the effects of defined numbers of or particles o n individual mammalian cells is helpful in understanding risks associa ted with exposure to radon. This paper reports the first biological da ta generated using the single-particle/single-cell irradiation system developed at Pacific Northwest Laboratory. Using this apparatus, CHO-K 1 cells were exposed to controlled numbers of 3.2 MeV alpha particles, and biological responses of individual cells to these irradiations we re quantified. Chromosomal damage, measured by the induction of micron uclei, was evaluated after no, one, two, three or five particle traver sals. Exposures of up to five alpha particles had no influence on the total numbers of cells recovered for scoring. With increased numbers o f alpha particles there was a decrease in the ratio of binucleated to mononucleated cells of 3.5%/hit, suggesting that alpha particles induc ed dose-dependent mitotic delay. A linear hit-response relationship wa s observed for micronucleus induction: Micronuclei/binucleated cell = 0.013 +/- 0.036 + (0.08 +/- 0.013) x D, where D is the number of parti cles. When the estimated dose per alpha-particle traversal was related to the frequency of induced micronuclei, the amount of chromosomal da mage per unit dose was found to be similar to that resulting from expo sures to alpha particles from other types of sources. Approximately 72 % of the cells exposed to five a particles yield no micronuclei, sugge sting the potential for differential sensitivity in the cell populatio n. Additional studies are needed to control biological variables such as stage of the cell cycle and physical parameters to ensure that each cell scored received the same number of nuclear traversals. (C) 1996 by Radiation Research Society