LIFE01200604005 Shri Somnath Ghosh - Homi Bhabha National ...

CHAPTER 1
INTRODUCTION
becomes potentially cytotoxic. Therefore the onus lies on non gap junction mediated cell
communication.
Evidence for some forms of bystander effect has been suggested also by conventional
irradiation with low doses. One of the first studies in this field has showed a significant,
unexpected increase in the frequency of sister chromatid exchanges (SCEs) after
exposure of Chinese hamster ovary (CHO) cells to very low doses of alpha particles,
from 0.03 to 0.25 cGy [220]. While about 1% or less of the cells were actually traversed
by a particle track, 30–45% of the individual cells showed increased levels of SCE. This
suggests that genetic damage following exposure to very low doses of light ions may
occur also in non directly-irradiated bystander cells.
The studies discussed above strongly suggest a role of extranuclear- and possibly
extracellular-targets in the propagation of certain damage types after irradiation with very
low doses of light ions or treatment with ICM. Experiments allowing the identification of
specific targets for such phenomena can be of great help to better understand the
underlying mechanisms and to quantify the relative contributions of different targets.
This kind of studies is now possible due to the increasing number of microbeam facilities.
Such facilities in which cells are individually irradiated by a predefined exact number of
particles allow the effects of individual particle traversals to be assessed, and these
methods have become a useful tool in the study of bystander responses [221, 222]. Such
studies suggest a major role of cell-to-cell communication via gap-junctions [223].
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