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The induction of HPRT-mutations and survival of Chinese hamster cells (line B11ii-FAF28, clone 431) were studied after irradiation by 4He and 12C-ions of various LET (20-360 keV/micrometers), produced by the U-200 heavy ion accelerator. The RBE increases with LET up to the maximum at 100-200 keV/micrometers and then decreases. Cytogenetic analysis was performed on the HPRT-mutant subclones selected from unirradiated Chinese hamster V-79 cells and from HPRT-mutant subclones that arose after exposure to gamma-rays, 1 GeV protons and 14N-ions (LET-77 keV/micrometers), produced by the synchrophasotron and the U-400M heavy ion accelerator. Slow growing mutant subclones were observed. The cytogenetic properties of individual clones were highly heterogeneous and chromosome instability was observed in both spontaneous and radiation-induced mutants. Chromosome instability was highest among spontaneous mutants and decreased with increasing LET., (c2002 COSPAR. Published by Elsevier Science Ltd. All rights reserved.)

Inactivation and induction of mutations in the HGPRT locus in Chinese hamster cells after irradiation with accelerated heavy ions in the LET range of 20 to 367 keV/micron were studied. In both cases, inactivation and induction of mutations, the LET dependence of RBE is described by a curve with a local maximum in the range of 80 to 100 keV/micron. The maximum RBE value for the mutagenic action is almost twice as high as that for inactivation. However, the RBE coefficients of the mutation induction criterion for a certain level of cell-survival is lower significantly and tend to decrease with an increase in inactivation. The obtained data show that the mutagenic effects, induction of chromosome aberrations, and deaths have their origins in the same kind of primary damages, i.e., double-strand breaks of DNA.

The peculiarities of mutation induction and cytogenetic characteristics of spontaneous and radiation-induced HPRT mutant clones have been studied. The linear-quadratic dependence of the mutation induction on radiation dose has been found. High heterogeneity of cytogenetic parameters (aneuploidy and chromosome aberration frequency) has been shown in the mutants.