Effect of lignocaine on the responses produced by depolarizing agents at the chick neuromuscular junction

The effect of lignocaine on the depolarization and contracture responses produced by acetylcholine (ACh) or tetraethylammonium (TEA) was studied in the isolated chick biventer cervicis (BVC) nerve-muscle preparation using the moving fluid electrode technique. Lignocaine (37 mumol X 1-1-1.8 mmol X 1-1) produced concentration-dependent contractures in the chick BVC muscle. The contractures produced by lignocaine were not accompanied by membrane depolarizations. ACh (5.5 mumol X 1-1-11.0 mmol X 1-1) and TEA (0.48-24.0 mmol X 1-1) produced concentration-dependent depolarizations and contractures in the chick BVC muscle. Lignocaine (0.93 mmol X 1-1) greatly reduced the responses produced by ACh, while it markedly increased the contracture responses produced by TEA. The depolarizations produced by TEA were reduced in lignocaine (0.93 mmol X 1-1). It was concluded that the local anaesthetic lignocaine produces contractures in the chick BVC muscle. Lignocaine potentiates the contractures produced by TEA, while it greatly reduces those produced by ACh.