General Discussion 225 



have not shown a potassium deficiency as in muscle, but they have 

 shown a fall in intracellular bicarbonate, and therefore presumably 

 a fall in intracellular pH. These experiments have not, as far as I 

 know, been done with the heart muscle, but by analogy one would 

 predict that the same situation may occur: the fall in intracellular 

 potassium may be small, but the fall in intracellular bicarbonate 

 and intracellular pH may be comparable to that in the kidney, and 

 possibly greater. 



Fourman: Yes, unless you think as I did, that the fall in intra- 

 cellular pH is a result of the fall in intracellular potassium. 



Milne: Direct analysis of tissue does not appear to support that. 



Shock: The histological structure in Prof. Wallace's potassium- 

 deficient animal, which I presume was a young one, is quite similar to 

 the sections of muscle tissue from the old animals that Dr. Andrew 

 has prepared from our material, which show a reduction in potas- 

 sium content of the total muscle mass. There were fewer nice- 

 looking muscle fibres in Prof. Wallace's animal than we see in the 

 sections from the older animals, but there is a striking similarity 

 in that there are good-looking areas, as described by the pathologist, 

 with a lot of other material around them. I recall that a few years 

 ago there was quite a flurry about the electron microscopic studies 

 of mitochondria. In such pictures the mitochondria from cells of 

 old animals were presumed to look frayed and woebegone. Sub- 

 sequent experiments showed that dietary deficiencies and alterations 

 could produce similar changes in the mitochondria taken from cells 

 of young animals. If the few cellular changes we can observe in 

 older animals can be produced by nutritional and dietary alterations 

 in the young ones, it is possible that these 'age changes' are the 

 result of chronic malnutrition of the cells. This brings us to the 

 basic questions of what is adequate nutrition of a cell, and how can 

 it be maintained. 



Wallace: What is old and what is young? To me a 30-day-old rat is 

 quite young, while to Dr. Widdowson it is as old as Methuselah. 



Shock: To me a 10-12-month-old rat is a husky young adult, and 

 when I talk of an old animal I mean one that is 24 months old or at 

 least is at an age when 50 per cent of his contemporaries are dead. 



Wallace: Young rats made potassium-deficient do show morpho- 

 logical changes in skeletal muscle. These changes can be almost 

 completely reversed in as little as 36-48 hours after potassium 

 administration. The lesions in cardiac muscle do not show this 

 rapid type of healing. It would be interesting to see if your old rats 

 have a slower repair time. Dr. Hingerty has already mentioned 

 that older rats chemically repair potassium deficiency more slowly 

 than do the young ones. 



AGEING — IV — 8 



