We investigated high- or low-dose irradiation-responsive proteins using 
proteomics on two-dimensional (2D) PAGE, and the effects of ageing on cell 
responses to radiation in variously aged rat astrocytes. After 5 Gy irradiation, 
the relative abundance of peroxiredoxin 2, an antioxidant enzyme, and latexin, 
an inhibitor of carboxypeptidase, increased. The induction of these proteins was 
suppressed by ageing, suggesting that the response to high-dose radiation 
decreased with ageing. The relative abundance of elongation factor 2 (EF-2) 
fragment increased 3 h and reduced 24 h after 0.1 Gy irradiation. Temporal 
enhancement of the EF-2 fragment due to low-dose irradiation was suppressed by 
ageing. Since radiation adaptive response in cultured astrocytes was observed 3 
h but not 24 h after 0.1 Gy irradiation and suppressed by ageing as previously 
reported, alteration of the EF-2 fragment corresponded to the radiation adaptive 
response. We also examined phospho-protein profiles, resulting in the relative 
abundance of phospho-EF-1beta and phospho-beta-actin being altered by 0.1 Gy 
irradiation; however, ageing did not affect the alteration of phospho-EF-1beta 
and phospho-beta-actin, unlike the EF-2 fragment. The results suggested that the 
EF-2 fragment was a possible candidate for the protein responsible for the 
radiation adaptive response in cultured astrocytes.