EFFECT OF DI-ISOPROPYL FLUORPHOSPHATE (DFP) ON ACTION POTENTIAL AND CHOLINESTERASE OF NERVE. III

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Abstract
In previous expts., the parallelism between irreversible abolition of the action potential and the irreversible inhibition of cholinesterase in nerves exposed to DFP, had been demonstrated as a function of time. Now, comparing the rate of irreversibility of the two processes in nerves of cold- and warm-blooded animals, the parallelism has also been established as a function of time. When the superior cervical sympathetic nerve of the cat is exposed to 4 mg. of DFP/ml., at 37[degree]C, the action potential is abolished within 2-5 min. but recovers when the nerve is returned to Ringer soln. On additional exposure of the nerve to DFP for 20 min. the action potential is abolished irreversibly. In the bullfrog, sciatic nerve at room temp., and in the lobster cord, approx. 100-120 min. are needed for irreversible effects. The increase in rate thus corresponds to that expected from the Q10 of the irreversible inactivation of cholinesterase which is approx. 2. In contrast to the mode of action of DFP, the abolition of the action potential and the inhibition of cholinesterase by eserine, under the same conditions and in the same concns., is always easily reversible. In the present paper, this reversibility of the eserine effect has been demonstrated on the superior cervical sympathetic nerve of the cat and on the bullfrog sciatic nerve. The observations offer strong additional proof for the correlation between conduction and cholinesterase activity.