OILMAN: EFFECTS OF DRUGS ON NERVE ACTIVITY 555 



esterase concentration, prompted a repetition of this type of study. 

 Moreover, advantage was taken of the opportunity to compare the 

 effects of a reversible (physostigmine) and an irreversible anticholin- 

 esterase. The nerve action potential was employed as an index of 

 effect on transmission. It was argued that, whereas both types of anti- 

 cholinesterase agent should affect the nerve action potential in the 

 same manner, assuming acetylcholine to play a major role in trans- 

 mission, the action of physostigmine should prove reversible, that of 

 diisopropyl-fluorophosphate, irreversible. The possibility that phy- 

 sostigmine might not gain access to those structures accessible to di- 

 isopropyl-fluorophosphate was avoided, as far as possible, by employ- 

 ing the alkaloid base, as well as the salicylate salt. 



Two types of experiments were performed. In the first, isolated 

 nerves of bull frogs and of cats were mounted in a moist chamber, 

 placed in a constant temperature bath of appropriate temperature. A 

 portion of the nerve was looped into a small chamber containing 

 Ringer's solution. Following the recording of control action potentials, 

 the effects of the various drugs were ascertained. When the isolated 

 nerves of the cat or the bull frog were exposed to 0.01 molar physostig- 

 mine salicylate, no detectable change in the action potential was ob- 

 served. However, when the solution containing the salicylate salt of 

 physostigmine was replaced by the alkaloidal base, the action potential 

 disappeared within a period of 10 minutes. Washing the nerve with 

 Ringer's solution restored the action potential completely. Thus, the 

 water-soluble salicylate salt was devoid of action, whereas the lipoid- 

 soluble alkaloidal base blocked transmission. 



Similar experiments were then performed, by exposing the nerve 

 to 0.02 molar diisopropyl-fluorophosphate. Again, the action poten- 

 tial disappeared within a few minutes. It only remained to demon- 

 strate the irreversibility of this block, in order to attribute the effect 

 to the inactivation of cholinesterase. However, washing the nerve 

 restored the action potential, despite the fact that the action of di- 

 isopropyl-fluorophosphate was supposedly irreversible. In view of 

 this surprising result, experiments were performed to determine the 

 extent of the wash necessary to restore the nerve and the speed at 

 which the action potential returned. During the course of these studies, 

 it was observed that it was only necessary to remove the nerve from 

 contact with the solution containing diisopropyl-fluorophosphate, to 

 restore the action potential completely. Thus, the conduction defect 

 could not have been related to an inhibition of cholinesterase. 



It was not possible, in the experiments on the isolated nerve, to meas- 

 ure accurately the extent of inhibition of cholinesterase, for the reason 



