Effects of some intravenous anaesthetics on the contractile responses produced in the chick biventer cervicis skeletal muscle.

The effects of some intravenous anaesthetics, in low and high concentrations, on the contractile responses produced in the chick biventer cervicis skeletal muscle were studied using electrophysiological and pharmacological techniques. The anaesthetics used were methohexitone sodium, thiopentone, ICI 35 868 (propofol, diprivan), althesin and etomidate. The results showed that all these anaesthetics had a common mode of action at the chick neuromuscular junction. In low concentrations, they increased the amplitude of the indirectly-elicited twitch and tetanic contractions, whereas in high concentrations they reduced the evoked contractions and the contractures produced by depolarizing agents such as acetylcholine or tetraethylammonium. The results indicated that, in low concentrations, anaesthetics may stimulate skeletal muscle whereas in high concentrations they reduce the sensitivity of the postjunctional membrane to depolarizing drugs. The possibility that anaesthetics may block endplate ion channels was also discussed.