VOL. 4 (1950) 



PERMEABILITY AND NERVE FUNCTION, II 



103 



Fig. 8 is a curve obtained by plotting the rates of penetration of Ca*^ into the nerves 

 against time of exposure. It will be noted that the initial rate of exchange, extrapolated 

 to zero time, is quite high and com- 

 parable to the initial extrapolated «s 50 

 value for K (50 micromoles/ioo gm/ 

 min and 82 micromoles/ioo gm/min 

 respectively). _^ jo 



6^0 



Fig. 8. Rate of Ca penetration across the 

 membrane of the giant axon of Squid when 

 exposed to artificial sea water containing 

 0.012 M Ca^^Cl. The rate of penetration of 

 Ca** in micromoles (^M)/ioo g/min is 

 plotted against time of exposure in 

 minutes. 



5: 



20 



10 



xr: — 



<i >. 



10 20 



50 



100 

 Min. of exposure 



B. FACTORS INFLUENCING EXCHANGE OF Na AND K 



In view of the considerable individual variations of the ion content of these nerves, 

 it appeared advisable to modify the method of accumulation of data in studying the 

 effects of a number of factors on the ion exchanges across the nerve membrane. Instead 

 of collecting single values at varying periods of exposure, a large number of nerves 

 were exposed simultaneously under identical conditions and for the same period of 

 time. At least five values were obtained for a given condition and only the average values 

 utilized in carrying out comparisons. All exposures were limited to 30 min. They were 

 carried out at room temperature (22° C), except for the cases in which the Qjq of Na 

 and K exchange were studied. 



I- Qio^f -^^ ^^^ ^ exchange. Table IV contains the data obtained when nerves were 

 exposed to 0.39 M Na^^ CI + 0.13 M Na^* CI in artificial sea water for 30 min at 22° and 

 13° C respectively. At 22° C, the average of eight nerves gave a value of 9.5 millimoles/ 

 100 g while at 13° C the average of eight nerves was 8.6 millimoles/ioo g. This would 

 correspond to a Q^ of 1.22. 



TABLE IV 



EFFECT OF TEMPERATURE ON THE RATE OF PENETRATION OF Na 



Nerves exposed for 30 min to sea water at 22° and 13° C containing 0.39 M Na^^Cl + 0.13 M Na^^Cl. 

 Sj and Sj = standards. 



References p. 114. 



