AbstractLongicaudatine, a tertiary bisindole alkaloid isolated from the root bark ofStrychnos trinervis(Vell.) Mart. (Loganiaceae), antagonized in a noncompetitive manner, carbachol and histamine induced contractions of the guinea‐pig ileum and bradykinin responses in the rat uterus. The respective pD2' values (mean ± SE) were 4.61 ± 0.21, 4.98 ± 0.04 and 4.49 ± 0.01. Longicaudatine, unlike verapamil, had no effect on voltage dependent Ca2+channels, as it failed to inhibit KCI or CaCl2induced contractions of guinea‐pig ileum and depolarized rat uterus respectively. When compared with sodium nitroprusside, an antagonist of receptor operated Ca2+channels, longicaudatine produced a slower and weaker inhibition of noradrenaline induced sustained contractions of rabbit aortic strips. However, in the aorta, the alkaloid antagonized the intracellular calcium dependent transient contractions of noradrenaline and longicaudatine (IC50, 5.01 × 10−7M) was approximately 133 times more potent that procaine (IC50, 6.68 × 10−5M), a known inhibitor of the release of Ca2+from intracellular stores. Longicaudatine may exert nonspecific spasmolytic effects by acting on intracellular Ca2+stores, rather than on depolarization dependent or receptor operated