228 Discussion 



experiments where we do not add glucose in excess, the ATP in the store 

 near the hexokinase is not depleted. I understand that your glucose 

 concentrations are so high that you have no ATP left in this type of 

 store. 



Rocker: The glucose concentrations which we used were quite high, 

 of the order of the physiological blood concentration. But, as you can 

 see from our data, at no time was the ATP depleted ; in fact, the addition 

 of glucose increased ATP concentration rather than decreased it. The 

 initial dip in the graph, which is due to ADP formation, is only very 

 short-lived. 



Hess : We have also demonstrated this drop. The fact that there is a 

 constant minimum level of ATP per cell, together with other data, led 

 us to assume the occurrence of various cellular ATP pools; in fact, it 

 can be taken as evidence for it (see Hess, B., and Chance, B. (1959), in 

 preparation; Chance, B., and Hess, B. (1959). Science, in press). Thus, 

 this minimum ATP is in the mitochondria and not at the hexokinase. 



Backer: This is exactly the point I am trying to make. 



Hess : If one adds a very small amount of glucose, as we do, in the 

 range of 15 m-molar and titrates just a small amount of the ATP at 

 the site of the hexokinase, one does not see a large drop in the ATP 

 level. It should be emphasized that in simulation of the physiological 

 state we have to add a small amount of glucose, since the abdominal 

 cavity contains very low amounts of glucose. We must assume that 

 under physiological conditions the cells are idling between different 

 states. One of these states is defined by low-level glucose which pene- 

 trates into the cell and just controls the respiratory rate, keeping it at 

 its lowest level. 



Racker: I cannot quite agree on this point. I don't think we know 

 much about the in vivo rate of glucose utilization of ascites tumour 

 cells within the peritoneal cavity. I don't think we should be too im- 

 pressed by the fact that we don't find very much glucose when we analyse 

 the intraperitoneal fluid. As long as we have no information on the rate 

 of glucose delivery from the blood stream, we cannot estimate the rate 

 of its utilization. Similarly, if we find no oxygen in the ascites fluid, we 

 should not conclude that the ascites tumour cells do not respire. It is 

 quite possible that the rate of diffusion of glucose or oxygen is slower 

 than the rate of utilization. I would also like to point out that measure- 

 ments of glucose concentration in ascites fluid may be misleading 

 because of the time required for sampling. We are dealing with a heavy 

 suspension of actively metabolizing cells which can utilize a respectable 

 amount of glucose in a matter of a few seconds. 



Would you want to say that the intraperitoneal steady state concen- 

 tration of glucose is below the K^^ of hexosamine, which in ascites 

 tumour cells is below 10"* m? 



Chance: Dr. Hess pointed out that it was the rate of production of 

 ATP from the glucose hexokinase system, which was setting the pace of 

 respiration. 



Racker : I still do not see what that tells us about the rate of glucose 

 utilization. 



