ACTION OF IONIZING RADIATIONS ON 

 CELL CONSTITUENTS 



Maurice Errera 

 Laboratoire de Morphologic animale, Universite libre de Bruxelles 



In order to understand the mechanisms of the physical effects of radia- 

 tions, it is important to distinguish between primary and secondary effects. 

 From a l:)iochemical or biological standpoint, these must not be confused 

 with initial (or immediate) and late effects which occur through a chain of yet 

 unknown events. Effects observable in a biological system after very short 

 delays may be tentatively classified as initial. Amongst them, retardation 

 and inhibition of mitosis, chromosome breakages, mutations, have been 

 observed very shortly after irradiation, but often these effects become more 

 conspicuous if some time or several cell generations elapse before observa- 

 tion ; on the other hand unless very high dosages are used killing effects 

 are usually observable only after several cell divisions. Whether these 

 fundamental effects are related to one another is still an open question and 

 the answer will depend on whether it is possible to ascribe them to some com- 

 mon initial biochemical step. The search for cytological damage will help to 

 identify the cellular components liable to be altered initially : both damage 

 to the nucleus (chromosome breakage or stickiness, altered morphology of 

 the nucleolus) or to the cytoplasm (swelling, vacuolization, change in staining 

 of mitochondria) have been observed. 



Attacking the problem from the other end, physical chemists and bio- 

 chemists have usually looked for radiation effects on purified cellular com- 

 ponents treated in vitro (effects on lipids, proteins, polysaccharides or even 

 more simple molecules) . Unfortunately nothing proves that cell components 

 behave in a similar way outside and inside the cell, where they often belong 

 to complex structmes and where they are in close contact with numerous 

 protecting agents. 



In our opinion, it is of fundamental importance to look for effects on cel- 

 lular components which can be demonstrated immediately after irradiation : 

 the longer one waits, even if smaller dosages are used, the more numerous 

 will be the compounds liable to be altered by secondary biochemical re- 

 actions — small initial biochemical alterations (which as we have seen may be 

 direct or indirect for the physicist) may lead to important secondary effects 

 and it will become more and more difficult to trace the chain of reactions 

 induced by the radiations. We do not want to minimize the importance 

 of these secondary effects, which may have considerable biological conse- 

 quences, but for the biophysicist or the biochemist they will hardly help to 

 solve the fundamental mechanisms one is looking for. 



It is a priori difficult to predict which cellular compounds will be altered 

 when irradiated in vivo, and which will be the biological consequence of such 

 alterations : our knowledge of ' key ' constituents is still very limited. So 



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