A DISCUSSION OF SOME IMMEDIATE EFFECTS OF 

 X-IRRADIATION ON LIVING CELLS 



BARBARA E. HOLMES 

 DejKirtment nf Badiotherapeutics, University of Cambridge, Emjlnnd 



SUMMARY 



Attention is drawn to a few of the immediate bioeliemical effects of X-rays 

 mentioned in the hterature. 



Some of these may be due to radical or direct attack on enzyme systems or 

 cell strvictm*es. 



One difRciilty in discussing the initial effect of irradiation on cells is 

 to decide what we mean by this. Our target is liable to be that event 

 in which we are most interested at the time and, in any case, our ideas 

 are usually conditioned and limited by the ease of detection of the 

 effect ; in fact, by its manifest importance to the cell. 



Normally, also, we are considering effects which are irreversible or 

 only slowly reversible. By using special techniques of killing cells during 

 the course of irradiation, rapidly reversible changes can sometimes be 

 seen, for instance in the proportions of oxidized to reduced co-enzyme. 

 One is inclined to think that such changes and many reparable cyto- 

 plasmic injuries are unimportant. It seems possible that, though no 

 immediate dramatic effect is usually to be seen, part of the phenomenon 

 of ageing by irradiation may be the result of such causes. 



An immediate dramatic effect can be shown in the result of the 

 irradiation of the sporangiophore of Phycomyces. Forssberg (1960) 

 found that the elongation of the sporangiophore could be inhibited 

 temporarily by doses as low as 0-0005 r, a maximal effect being pro- 

 duced by 1 -0 r. The inhibition is quickly reversible when irradiation is 

 stopped. The mechanism of elongation is not fully known and it is 

 difficult to picture in what way it could be affected by such tiny doses. 

 If an enzyme or specific chemical substance is concerned, then it must 

 surely be directly connected with the elongating cell wall or the water- 

 imbibing membrane and some energy-transporting mechanism must be 

 imagined. Forssberg has found an accumulation of lactic acid during 

 this period of inhibition of elongation and also an abnormal distribution 



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