Discussion 33 



representative sample of what is going on in the organism. Is tliis a fair 

 assumption? A second point is that most of the work has been done on 

 kidney shoes. Are kidney shoes representative of the whole organism, or 

 only of the kidney tissue? 



Davson: I was thinking in terms of the tissues that I have worked with 

 — not the kidney, but musoles and red oells. As far as I oan see, the 

 results of the work on the kidney cortex are essentially similar to those 

 obtained on the muscle. However there might be a confusing situation if 

 you got a lump of kidney tissue with fairly intact tubules as well as not so 

 intact tubules ; they could be accumulating sodium and indulging in their 

 special secretory processes which are quite different from those in nmscle. 

 I have never looked with any approval on work done with slices of these 

 specialized tissues. 



Fejfar : Quite a lot of work has been done with kidney in Prague by Cort 

 and Kleinzeller (1956. J. Physiol., 133, 287) and that is why I asked you. 

 They support an active mechanism for sodium and passive mechanisms 

 for potassium and chloride. 



Davson: The active accumulation of potassium by most of the cells 

 that have been studied has not had to be specifically invoked. It is almost 

 an unnecessary hypothesis for muscle, but on the other hand one finds 

 that the active transport of sodium is linked with that of potassium. If 

 one is an active process, the other must be too. From the responses to 

 changes of environment, one must say that potassium is following its 

 gradients of electrochemical potential. On the other hand, when the 

 matter is studied with isotopes and it is found out just how much sodium 

 is going in, it is seen that there is a linkage between the amount of sod- 

 ium crossing the membrane and the amount of potassium. It is not a 

 rigid linkage, however. 



Fejfar: Cort and Kleinzeller find that the amount of potassium crossing 

 the membrane is usually smaller than the amount of sodium. 



Davson : Yes, there is a 2 : 1 ratio. In the inuscle it is a certain propor- 

 tion, and in the red cell it is a different proportion. Certainly in the red 

 cell an active accumulation of potassium as well as of sodium has to be 

 invoked. 



Fejfar: Roguski in Poland claims that one can judge general cellular 

 metabolism from the red cells themselves. We do not agree because the 

 red cell is not a respiring cell. Neubauer (personal communication) has 

 made a comparison of the water and electrolyte changes between muscle 

 biopsy specimens and red cells, and he could not find any similarity be- 

 tween them. He came to the conclusion that you could not judge 

 electrolyte changes from the red cell. 



Davson: That is quite true. The mammalian red cell metabolism is 

 different; it is largely anaerobic, whereas the muscle and all the other 

 cells are mainly aerobic. 



Fejfar: I was surprised to hear you say that when cells are poisoned 

 there is not only an influx of sodium, but also of chloride. We were 

 taught that chloride does not usually enter cells in significant amounts 

 and that only sodium does this, so we judge the extracellular fluid by the 

 cliloride present. 



AGEING — IV— 2 33 



