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ACTIONS OF HEMICHOLINIUM (HC-3) ON NEUROMUSCULAR TRANSMISSION

E R EVANS, H WILSON

    British Journal of Pharmacology and Chemotherapy
    |June 1, 1964
    PubMed

    Insights

    Hemicholinium No. 3 causes a long-lasting neuromuscular block by reducing acetylcholine release from the nerve. This presynaptic action differs from other blockers and can be reversed by stopping nerve stimulation.

    Area of Science:

    • Neuroscience
    • Pharmacology
    • Muscle Physiology

    Background:

    • Neuromuscular blocking agents are crucial in anesthesia and critical care.
    • Understanding the precise mechanism of action of these agents is vital for optimizing their use and developing new therapies.
    • Hemicholinium No. 3 (HC-3) is a compound known to affect neuromuscular transmission, but its exact site of action requires further elucidation.

    Purpose of the Study:

    • To investigate the mechanism of neuromuscular blockade induced by Hemicholinium No. 3 (HC-3).
    • To differentiate the action of HC-3 from other neuromuscular blocking agents like tubocurarine.
    • To determine the presynaptic or postsynaptic effects of HC-3 at the neuromuscular junction.

    Main Methods:

    • Utilized the tibialis anterior muscle-sciatic nerve preparation in anesthetized cats.
    • Administered HC-3 and assessed its effect on neuromuscular blockade.
    • Evaluated the muscle response to acetylcholine injections to test motor endplate sensitivity.
    • Investigated the effects of choline and anticholinesterase drugs on the HC-3-induced block.
    • Observed the response to tetanic nerve stimulation and the impact of suspending stimulation.

    Main Results:

    • HC-3 produced a slow-onset, long-duration neuromuscular block dependent on nerve stimulus frequency.
    • The drug did not alter muscle response to direct acetylcholine administration, suggesting no postsynaptic effect.
    • The block was antagonized by choline and only partially reversed by anticholinesterase agents.
    • Tetanic stimulation during the block was sustained, with slight posttetanic potentiation.
    • Temporary cessation of nerve stimulation relieved the HC-3-induced blockade.

    Conclusions:

    • The findings indicate that HC-3 acts presynaptically at the neuromuscular junction.
    • Its primary mechanism likely involves reducing acetylcholine release upon nerve stimulation.
    • HC-3's mode of action is distinct from postsynaptic blockers like tubocurarine.

    Keywords:
    ACETYLCHOLINEBIPHENYL COMPOUNDSBLOOD PRESSURECATSCHOLINECURARIFORM ANTAGONISTSEDROPHONIUM CHLORIDEELECTRIC STIMULATIONEXPERIMENTAL LAB STUDYGANGLIONIC BLOCKADERSNEOSTIGMINENEUROMUSCULAR JUNCTIONPHARMACOLOGYSCIATIC NERVE

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