GENERALITY OF THE ROLE OF ACETYLCHOLINE IN NERVE AND MUSCLE CONDUCTION

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Abstract
The abolition of conduction in nerves exposed to di-isopropyl fluorophosphate (DFP) has been attributed to the destruction of cholinesterase. In conjunction with many other biochemical and biophysical facts, these expts. support the assumption that the enzyme activity and, consequently, the removal of acetylcholine are essential events in the conduction of nerve impulses. In the present paper, evidence is offered that the role of acetylcholine in conduction is a general one. Different types of nerves and also striated muscle were exposed to inhibitors of cholinesterase (DFP and eserine). Reversible abolition of conduction was demonstrated under the same conditions as in the case of- motor nerves. As a sample of purely sensory nerves, the optic and the superficial ophthalmic of Raja erinacea were used. The splanchnic nerve of the bullfrog was used as a sample of a so-called adrenergic nerve. The effect of the anticholines-terases on muscular conduction was tested on the completely curarized frog''s satorius. The identical action of inhibitors of cholinesterase on the action potential of all these nerves and on that of muscle, makes it highly probable that the acetylcholine system plays an essential role in the conducting mechanism of all types of nerve and of muscle. As a corollary of these findings, presence of cholinesterase could be demonstrated in all these tissues and also in low invertebrates, like Planaria and Tubularia. The latter one, a hydrozoan coelenterate, is the lowest group of animals to possess a nervous system comparable to that of higher animals. In contrast, prostigmine, an equally powerful cholinesterase inhibitor, had no effect on muscle action potential. This suggests, as in the case of nerve, that methylated quaternary ammonium salts, like prostigmine, acetylcholine and curare, do not penetrate to the active surface of the nerve and muscle fiber except at the neuro-muscular junction.