The interaction between edrophonium (tensilon) and acetylcholine at the motor end-plate.

The effect of edrophonium (3-hydroxy-phenyl-dimethylethylammonium chloride) on the motor end-plate and its interaction with acetylcholine and carbachol has been investigated. Use was made of intracellular recording of membrane potential and of ionophoretic micro-application of drugs from single and twin-pipettes.Small doses of edrophonium potentiate the depolarizing effect of acetylcholine, but not that of carbachol. This action can be observed with doses of edrophonium which have no depolarizing effect by themselves. Large doses of edrophonium have some depolarizing action and, at the same time, inhibit depolarizations produced by carbachol. After treatment with neostigmine, edrophonium fails to potentiate the acetylcholine response. The observations are in agreement with the view that the principal action of edrophonium on the neuromuscular junction is that of a potent and rapidly acting anticholinesterase.