Neuromuscular Blocking Action of Alkaloids from a Japanese Crude Drug “Shin-I” (Flos Magnoliae) in Frog Skeletal Muscle

From the dried buds of Magnolia salicifolia M AXIM , d -coclaurine ( 1 ), d -reticuline ( 2 ), 1 -N-methylcoclaurine ( 3 ) and yuzirine ( 4 ) were isolated. Fifty percent inhibitory doses (µM) in acetylcholine (ACh, 27.5 µM)-induced contraction of frog skeletal muscle were as follows: d -tubocuraine ( d -TC) 3.09, 2 93.2, 3 211, 1 467 and 4 more than 945. 4 (94.5 and 315 µM) increased the ACh-induced contraction. Indirectly stimulated twitching of frog nerve-muscle preparations were completely blocked by the following doses (µM): d -TC 1.47, 1 31.1, 2 239 and 3 more than 257. 1 , 2 and 3 did not or only slightly block directly stimulated twitching. In contrast 271 µM 4 blocked the directly stimulated twitching. Key Word Index Magnolia salicifolia - Magnoliaceae - Coclaurine - Reticuline - Methylcoclaurine - Neuromuscular blocking action