Factors Governing Ion Transfer in Nerve 



ABRAHAM M. SHANES 



National Institute of Arthritis and Metabolic Diseases, 

 National Institutes of Health, Bethesda, Maryland 



THE PROBLEMS of ncrvc physiology are in large measure identical with 

 those of most other cells. In common with other biological systems, 

 nerv^e fibers contain a high intracellular potassium concentration and small 

 quantities of sodium and chloride, while the medium is low in potassium and 

 high in sodium and chloride. Associated with this is a potential difference — the 

 ^resting' potential — between the protoplasm and the external environment, the 

 interior usually being negative relative to the exterior. There is reason to 

 believe that the peculiarities of ion distribution are intimately related to this 

 bioelectrical potential; indeed, a number of exponents of this view have pro- 

 posed specific relationships between the ionic concentrations and the resting 

 potential which currently are being subjected to rigorous experimental tests. 



I shall concern myself largely with this aspect of ion distribution. Many 

 re\aews have appeared recently on ion movement accompanying nerve activity, 

 as deduced particularly for cephalopod giant axons (e.g., 20, 21, 25). Only a 

 few remarks regarding the recovery processes associated with impulse produc- 

 tion will be attempted. Where possible, references have been selected to keep 

 the bibliography short. Additional detailed papers will be found in the literature 

 quoted. 



Before embarking on details, I should like to point out that neurophysiology 

 clearly reflects the advantages accruing from the comparative approach. Frog 

 nerve has, of course, always been a favorite because of its general availability; 

 frogs are easily obtained and stored and the sciatic nerves are dissected out 

 readily for study and survive well under i/z vitro conditions. Invertebrate nerves, 

 such as from the crab, have been used because of their faster penetrability by 

 experimental agents, but survival is not as good. With the rediscovery of the 

 giant axon of the squid, the possibility of inserting microelectrodes and of 

 analyzing axoplasm directly ushered in a new era of quantitative precision in 

 electrical measurement and chemical analysis which is filling many pages of the 

 current literature. A serious drawback continues to be the limited survival in 

 vitro of cephalopod and crab preparations, deterioration in better fibers be- 

 coming evident at best after a few hours (28, 29, 46) ; however, the effectiveness 

 with which Cole, Hodgkin and many others have exploited the advantages of 



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