VOL. 4 (1950) 



PERMEABILITY AND NERVE FUNCTION, II 



109 



TABLE X 



EFFECT OF X-RAY IRRADIATION ON THE RATE OF PENETRATION OF Na 



Nerves irradiated with 50000 R and 125000 R respectively in natural sea water and then exposed 

 for 30 min to artificial sea water containing. 0.39 M Na^^Cl +0.13 M Na^^Cl. Sj and S2 = standards. 



DISCUSSION 



From the results obtained upon exposure of nerves to sea water, at rest, containing 

 radioactive K*^, it can be seen that part of the K of the nerve interior is in dynamic 

 equihbrium with that in the outer bathing medium. The lack of exchange of approxi- 

 mately 90% of the K^^ under these conditions is unexplained. It appears that most of 

 the K inside the nerve is not easily lost by the cell. Once the free, easily diffusible K 

 has been exchanged for K''^, the rate of K exchange falls to a very low level. This is in 

 good agreement with the observations of Hevesy and Hahn on rabbit muscle and red 

 blood cells^*, of Steinbach on Thyone briareus muscle^^, and of Heppel on rat muscle^^. 

 In all of these investigations no more than 10-30% of the total K content of the tissues 

 under investigation was exchangeable at rest. 



In an effort to explain the difficulty of incomplete K exchange essentially two 

 theories have been discussed. The one considers the possibility that the K is present 

 in bound form. The idea has been proposed that a K salt of an unknown organic acid 

 with a very low dissociation constant exists. As emphasized by Krogh^, there is no 

 evidence foi the existence of bound K and from a theoretical basis, it appears doubtful 

 that it can exist. Hill and Kupalov^' have shown that all the K inside the muscle cell 

 is required to be in ionic form in order to account for the osmotic pressure. Moreover, 

 its presence in ionic form is necessary to insure the neutral reaction. Another possibility 

 discussed is the presence of K impermeable barriers inside the cell. No such structures 

 are known. The reasons for exchange of only a small fraction of the total K cannot 

 be resolved at present. 



References p. 114. 



