io6 



M. A. ROTHENBERG 



VOL. 4 {1950) 



inherently indirect. In spite of the fact that the methods and materials employed are 

 different, the agreement is surprisingly close in the three cases. 



3. Effect of inhibitors of acetylcholine-esterase on the ion exchange. The effects of two 

 inhibitors of acetylcholine-esterase were studied on the rate of exchange of Na and K 

 in these fibres. In Table VII are given the results obtained when giant axons were 

 exposed for 30 min to 0.022 M diisopropyl fiuorophosphate (DFP) in sea water containing 

 0.013 M K*2C1. DFP at this concentration is capable of abolishing nerve conduction 

 within approximately 2 min^^ and the action of this compound can probably be attri- 

 buted exclusively to the inactivation of the enzyme^^. The average of five nerves exposed 

 to sea water containing DFP and K^^ gave a value of 1.08 milHmoles K/ioo g while 

 exposure to sea water for the same period of time in the absence of DFP gave a value 

 of 1. 31 millimoles/ioo g. Assuming, as above, that the average diameter of these fibres 

 is 500 [X (area of i g cylinder of axoplasm being equal to 80 cm^), then one obtains a value 

 of 5.5-10"^ mole/cm^/min as the rate of exchange of K in sea water at rest. In the pre- 

 sence of DFP this rate falls to 4.5 -lO"-^ mole/cm^/min. This would correspond to a 

 decrease of i.c-io"^ mole/cm^/min in the presence of DFP. Although the concentration 

 of K*2 in the axoplasm is smaller in the presence of DFP than in its absence, this result 

 does not indicate a deci eased permeability. In view of the concentration gradient be- 

 tween the inside of the axon and its outer environment an increase in permeabihty 

 may lead to an increase of the K outflow from the interior. The K*^ penetrating from 

 the outside may share the same fate and the final inside concentration will eventually 

 be smaller than that under normal conditions. 



TABLE VII 



EFFECT OF DFP ON THE RATE OF PENETRATION OF K AND Na 



Nerves exposed to 0.022 M DFP in sea water containing either 0.013 M K'l^Cl or 0.37 M Na'^'Cl -f- 

 0.13 M Na^^Cl. Si and Sj = standards. 



This view is confirmed by the effect of the DFP on the Na movement. Table VII 

 gives the results obtained when nerves were exposed to DFP in the same concentration 

 as above (0.022 M) in the presence of 0.13 M Na^^Cl + 0.37 M Na^^Cl in the sea water. 

 The mean of nine nerves exposed to DFP in sea water gave a values of 16.4 millimoles 

 References p. 114. 



