VOL. 4 (1950) 



PERMEABILITY AND NERVE FUNCTION, II 



10'; 



Na/ioo g as compared to 9.5 millimoles/ioo g when exposed to sea water in the absence 

 of DFP. This would correspond to a rate of penetration of Na of 4.o-io~^/cm2/min in 

 the absence of DFP and a penetration of 6.9-10"^ mole/cm^/min in the presence of 

 DFP, assuming the average fibre diameter to be 500 /<. The rate of Na penetration has 

 increased markedly. This could be expected on the basis of the concentration gradient 

 in the event of increased permeability. It may be noted that the Na penetration has 

 increased to a greater extent than the K penetration has decreased. Considering the 

 difference in the rates of entrance of Na and K, it has to be kept in mind that in the 

 experiments described, only the penetration of ions into the interior has been determined. 

 No measurements have been carried out in respect to the leakage of K. If the amount 

 of K actually passing from the inside to the outside were considerably increased, this 

 would not be indicated by the method used. 



The effect of eserine, another inhibitor of acetylcholine-esterase, on the rate of Na 

 penetration into the nerve was also studied. The results are given in Table VIII. It will 

 be noted that 13.2 millimoles Na/ioo g enter these nerves in the presence of 0.019 ^ 

 eserine in the sea water containing 0.13 M Na^'^Cl + 0.37 M Na^^Cl. This would corre- 

 spond to a rate of exchange of Na of 5.5-10"^ mole/cm^/min in the presence of eserine 

 as compared to 4.0-10"^ mole/cm^/min in its absence, again assuming the average 

 fibre diameter to be 500 /n. The above value is the average of ten nerves and, as in the 

 other experiments, nerves were exposed for 30 min to the eserine-containing sea water. 

 Eserine, in the concentration used, abolishes nerve conduction reversibly within 5-15 

 min. The time required to abolish the action potential of these nerves shows considerable 

 variation in the case of eserine and is closely dependent upon the p^ and other factors^^. 

 Air o-xidation of the eserine proceeds rapidly at the p^ employed (7.7-8.0) and therefore 



TABLE VIII 



EFFECT OF ESERINE ON THE RATE OF PENETR.\TION ON Na 



Xerves exposed to 0.019 M eserine in sea water (pn 7.7-8.0) containing 0.37 M Na^'^Cl -\- 0.13 M 



Na^*Cl. S, and S, 



Standards. 



References p. 114. 



