ANTAGONISM OF SUCCINYLCHOLINE BLOCKADE OF THE MAMMALIAN NEUROMUSCULAR JUNCTION

¹ Australian Defence Scientific Service, Defence Standards Laboratories, Melbourne, Australia

A study was made of the mode of action of drugs which prevent or alleviate blockade of the rat phrenic nervediaphragm preparation resulting from succinylcholine (SCh) or decamethonium (ClO). The mechanism of SCh or ClO antagonism differed among the drugs used, although basically it could be related to an increase in the presynaptic release of acetylcholine. Tetraethylammonium and triethylcholine appeared to act by prolonging the nerve terminal action potential and thus increasing the safety margin for acetylcholine release. They were able to relieve partially blockade due to low Ca⁺⁺ or high Mg⁺⁺ solutions. Oximes related to pyridine-2-aldoxime methiodide and methoxyambenonium were only able to relieve SCh or ClO blockade in the presence of physiologic concentrations of Ca⁺⁺ and Mg⁺⁺. In low Ca⁺⁺ or high Mg⁺⁺ solutions they accentuated SCh blockade and acted as partial agonists. It is postulated that effective agents compete with SCh or ClO at a presynaptic site, where they share the facilitatory effects of these compounds but have little depressant effect.

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