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 × 10^?6 ?5.5 × 10^?4M) and acetylcholine (ACh) (5.5 × 10^?6 ? 1.1 × 10^?2M) produced large depolarization and contracture responses in the isolated chick biventer cervicis (BVC) muscle. These responses were greatly reduced by methohexitone (8.8 × 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.