INITIAL RADIATION DAMAGE AT SUB-CELLULAR LEVEL 



5 



DOKS DAMACK OF A XISIliLI-: STlirCTlTHK 1{K( ilTLAI{L^■ I'K IICIIDH 



CKIJ. I)1-:ATH? 



The i)r()l)lein ot tiiuliiiu the nature of the initial eheiiiical lesion in 

 cell death would be siin])lilied if this effect could be associated with 

 damage of a particular organelle, such as the chromosome. No generali- 

 zation is, however, possible and not even the relative iniiK)rtance of the 

 cytoplasm and the nucleus has been resolved. In certain cells (insect 

 e(f(rs for instance) the lesion of the nucleus seems to be all important 

 but in other cells (amoebae, amphibian ovarian eggs) the contribution 

 of the cyto])lasm is certainly very great (for ref. see Bac(( and Alex- 

 ander, 1901). 



\Vhile some cells such as lymphocytes, spermatogonia and oocytes 

 are killed outright (i.e. interphase death) by a few hundred rads, most 

 manmialian cells need rather large doses for this to occur and, in general, 

 they are more sensitive to mitotic death : that is, they will divide once 

 or twice before division stops though the cells continue to grow in size. 



Fig. 1. Effec-t of X-rays (220kV at 300+ inin) on growth of mouse leukaomia colls in 



tissue culture (Alexander and Mikulski. 1!»»)0) (The cells were in suspension and fully 



oxygenated when irradiated). 



Figure 1 illustrates this effect for mouse leukaemia cells in tissue culture. 

 Until the cell number has doubled, no effect of radiation with doses of 

 300r or less was seen, then cell division ceases (with 30()r in case of 

 90 per cent of the cells) and the damaged cells increass in size. (Alex- 

 ander and Mikulski, l!»t)()). The majority grow to about double the 

 normal volume but about a quarter of them continue to gro\\' and form 



