VOL. 4 (1950) 



PERMEABILITY AND NERVE FUNCTION, II 



105 



TABLE VI 



EFFECT OF ELECTRICAL ACTIVITY OF THE NERVE ON THE RATE OF PENETRATION OF Na 



Nerves were stimulated at a rate of 100 times per second for a period of 30 min in sea water containing 

 0.39 M Na23Cl + 0.13 M Na^^Cl at 22° C. S^ and Sj = Standards. 



activity, a quantity of K has been lost by the nerve to the sea water equivalent to the 

 Na which penetrated during the same period. In the case under consideration, this would 

 be equivalent to a loss of 6.4 millimoles K/ioo g of axoplasm. This loss appears to be 

 very high since, as discussed earlier, at rest a maximum of 2.5 milHmoles K/ioo g are 

 easily exchangeable. 



A few calculations concerning the exchange of ions during activity of the nerve 

 may be of interest. The average diameter of the stellar nerve may be assumed to be of 

 the order of 500 fx. An axoplasm cylinder of r = 0.025 cm and weighing i g would 

 have a surface area of 80 cm^. Since an increased exchange of 6.4 millimoles Na/ioo g 

 (or 6.4-10"^ mole/g) has been demonstrated for a nerve which had been stimulated 

 1.8 -lo^ times (100 per second for 30 min), it follows that 6.4-10"^ mole/g divided 

 by 1.8-10^ or 3.6- io~i° mole/g/impulse of Na penetrated into the axoplasm of the nerve 

 from the sea water. This value corresponds to 4.5 • iq-^^ x^q\q of Na penetrating/cm^/im- 

 pulse. It has been reported by Pumphrey and Young^ that the diameters of these 

 giant nerve fibres of Squid usually vary from 280 to 720 // in diameter and may in some 

 cases by as large as 1000 /t (i mm). If one calculates the values of Na which would 

 penetrate per cm^ per impulse for the usual extremes in the size of the fibres under the 

 above conditions, one obtains the values 2.6-10-^- and 6.5 •lO"!^ mole/cm-/impulse for 

 the smaller and larger diameters respectively. If one assumes that the increased Na 

 penetration during activity is equivalent to the K loss during the same period, as the 

 work of several investigators indicates, then it follows that the transfer of 4.5 -10"^^ 

 mole/cm^/impulse of K has occurred during the period of nerve activity. This value 

 is in excellent agreement with that indirectly calculated by Hodgkin and Huxley^ 

 on the basis of the changes in membrane conductivity which occur in single fibre 

 preparations of Carcinus maenus nerves during normal conduction. They obtained a 

 value of i.7-io~i2 mole/cm^/impulse. The value is also in good agreement with that 

 obtained by Keynes^". This investigator soaked multifibre preparations of Carcinus 

 nerves in K^2_ Upon stimulation he found the leakage of 2.1-10-12 mole/cm^/impulse. 

 The data with Na^*, Hke those of Keynes, are direct. The method of Hodgkin and 

 Huxley, although most ingenious, necessitates numerous assumptions and is therefore 

 References p. 114. 



