The ionic permeability of nerve membranes 



Nastuk, W. L. and Hodgkin, A. L. (1950). The electrical activity of single muscle 



fibres. J. cell. comp. Physiol. 35, 39-73. 

 Shanes, A. M. (1951). Factors in nerve functioning. Fed. Proc. 10, 61 1-62 1. 

 Ussing, H. H. and Zerahn, K. (1951). Active transport of sodium as the source of 



electric current in the short-circuited isolated frog skin. Acta physiol. scand. 23, 



1 10-127. 



Discussion 

 Chairman: J. Bracket 



jV. Myant. What ionic movements occur across the membrane between the nodes 

 in a myelinated mammalian nerve? 



R. D. Keynes. The experiments of Huxley and Staempfli (1949: J. Physiol. 108, 

 315-339) showed that there was only a small outward current, probably carried by 

 the K + ions, through the myelin sheath. In contrast to the larger currents flowing in 

 and out at the nodes, this could be explained as a purely passive current due to the 

 potential change acting on a resistance and capacity in parallel. 



R. J. Goldacre. Has any attempt been made to follow visually the course of active 

 transport of ions in nerve by the use of cationic dyes ? Although the emphasis is on 

 the specificity of these pumps, it is difficult to think that a dye like neutral red would 

 not be taken up by nerve to an extent which would perhaps be sufficient, in the 

 case of a giant axon, for its course to be followed under the microscope. 



R. D. Keynes. We have never seriously investigated the penetration of dyes into giant 

 axons. Dyes injected into giant axons seem to diffuse as far as the membrane and 

 no further. 



J. E. Harris. Is there any connexion between the phenomena you have just described 

 and the very active uptake by nerves of methylene blue ? 



R. D. Keynes. I do not know of any physico-chemical connexion between the activity 

 in a nerve and the uptake of methylene blue; but I suppose that it is conceivable 

 that the dye might enter at the nerve terminals during the non-specific increase 

 in permeability which is thought to occur as a result of liberation of acetylcholine. 



49 



