Enhancing effect by nicotinic acetylcholine receptor channel blockers, including β-eudesmol, on succinylcholine-induced inhibition of twitch tension and intracellular Ca⁺⁺ in mouse diaphragm muscle

To elucidate the mechanism of neuromuscular block by succinylcholine, nerve-evoked changes in intracellular Ca⁺⁺-aequorin luminescence and twitch tension were measured simultaneously in the presence of several different types of blockers for the nicotinic acetylcholine receptor channel. Mouse diaphragm muscles were pretreated for 30 to 60 min with 3 to 40 μM bupivacaine, chlorpromazine, phencyclidine and β-eudesmol. The effects of these noncompetitive blockers on the succinylcholine-induced response were also compared with those for pancuronium. These channel blockers potentiated (2-to 10-fold) both the blocking effects on intracellular Ca⁺⁺ and twitch tension of succinylcholine (13-100 μM), but not the pancuronium (0.3-1.1 μM)induced block. These channel blockers also suppressed succinylcholine (1.3-5 μM)-induced enhancement of evoked Ca⁺⁺ transients. On the other hand, the channel blockers inhibited the succinylcholine (2.5-100 μM)-induced increase in basal Ca⁺⁺ transients. These results suggest that neuromuscular block induced by succinylcholine is mainly due to desensitization of the nicotinic acetylcholine receptor.