Discussion 223 



for example, we observed that when we had labelled lipids in the form of 

 egg-yolk then it all appeared very nicely in the ascites tumour. 



Forssberg: May I ask if you are doing these experiments in an atmos- 

 phere of oxygen, because our experiments were carried out under rather 

 anaerobic conditions. 



Popjak: These were aerobic, not in pure oxygen but in air. 



Forssberg: According to Christensen and Riggs (1952, J. biol. Chem., 

 194, 57) there is a rapid uptake of amino acids in ascites cells against a 

 strong concentration gradient. We ourselves found that 5 minutes 

 after an intraperitoneal injection the uptake was already very high and 

 was quantitatively similar in X-rayed and control cells. The glycine 

 seems to enter the cells directly from the intraperitoneal injection. 



Popjak: I am not suggesting that this might be the case for all cell 

 constituents, but it might be that in certain cases the preformed sub- 

 stances from plasma are taken out through the ascitic fluid. 



Krebs: Your last slide rather suggests that the conversion of lactic and 

 pyruvic acid into acetic acid is increased, and the two products of 

 acetyl coenzyme A, acetoacetate and citrate, are present in higher con- 

 centration. I wonder whether any other experiments would be in agree- 

 ment with this conclusion, that you get a more rapid oxidation. 



Forssberg: Oxygen tension in the ascites fluid is rather low. On a 

 molar basis the concentration of acetoacetic acid seems to be higher 

 than that which corresponds to a condensation of pyruvic acid? It 

 appears, however, from the analysis of the fluid that these substances 

 begin to leak from the cells almost immediately after irradiation ; there- 

 fore, quantitative determinations are uncertain. Mouse liver and 

 intestines which are irradiated at the same time as the ascites cells do 

 not show these changes, or at least show them only to a minor degree. 

 Whether any other similar experiments have been done, I do not know. 



Krebs: The decrease is not in arithmetical proportion to the increase. 



Lajtha: I think that the ascites cell cannot synthesize many things de 

 novo. On the other hand, the transformation and the transport can be 

 extremely quick. We gave ^-^C-formate in vivo to mice, and within 45 

 minutes the ascites cells became so heavily labelled that they were use- 

 less for autoradiography. Not only DNA but also RNA and proteins 

 were labelled. However, the same ascites cells in the same ascites fluid 

 in vitro in 3- to 6-hour cultures did not show any uptake of i*C-formate, 

 except small amounts in DNA thymine. With regard to the very 

 curious discrepancy between the depression in DNA synthesis and the 

 labelling of the DNA, I wonder whether that could be explained by 

 cells dying only in mitosis, and therefore no increase of DNA would be 

 observed in total of mass, but nevertheless the same cells were not 

 being inhibited in the synthetic period which is fairly long in these cells. 



Forssberg: The cells are carrying out some vital functions, e.g. 

 production of total cell mass (i.e. proteins and RNA), at a fairly normal 

 rate during the first 48 hours after irradiation and are "living" as judged 

 from vital staining; so I do not think there can be much cell death in 

 mitosis during this period. 



Lajtha: Is the cycle time constant in these cells? 



