Carbachol-methohexitone interactions at the chick neuromuscular junction: experiments with the moving fluid electrode technique.

The moving fluid electrode was used to record simultaneously the depolarization and contracture responses produced by drug action. Carbachol (CCh) (5.5 X 10(-6)-5.5 X 10(-4)M) acetylcholine (ACh) (5.5 X 10(-6)-1.1 X 10(-2) M) produced large depolarization and contracture responses in the isolated chick biventer cervicis (BVC) muscle. These responses were greatly reduced by methohexitone (8.8 X 10(-5) M). The concentration-response curves for ACh and carbachol in the control Krebs solution were shifted in the presence of methohexitone to the right in a non-competitive manner. The present results indicate that both ACh and carbachol act postjunctionally by depolarizing the membrane and producing contractures in the chick biventer cervicis muscle.