Effects of eserine and di-isopropyl-fluoro-phosphate (DFP) upon the demarcation potential of the sciatic nerve of toad were studied. Demarcation potential decreased over 80% of the initial following administration of the above mentioned anticholinesterases.
With the decrease of the demarcation potential, the action potential was also weakened. When the decrease of the demarcation potential proceeded under a certain limiting value, the action potential ceased. In this way the block was aroused in the axon by the effect of anticholinesterases. It seems certain that there exists intimate relationship between the demarcation potential and blocking effects of anticholinesterases.
When the nerve soaked in the anticholinesterase solution and stimulated repeatedly the velocity of decrease of demarcation potential increased rapidly. In such case, the time nescessary to block the nerve completely was shortened. Non-anticholinesterases such as procaine or KCl, which act as blocking agents, also decrease the demarcation potential of the nerve, but in slight degree.
It seems, there was no relationship between the blocking effect of non-anticholinesterases and the demarcation potential.
From these results, it could be concluded that the long persisting depolarization of the plasma membrane of the axon was the cause of anticholinesterase block.
According to the Nachmansohn's chemical theory of transmission of nerve impulse, acetylcholine becomes to persist for long time in the axon which is immersed in the anticholinesterases solution and causes a long persisting depolarization of the plasma membrane.
Above mentioned results are therefore favours Nachmansohn's theory.
