Objective:To investigate the pharmacological effect of Bupi Yichang (BPYX) pill on colonic contraction of rats and explore its underlying mechanism.Methods:The experiments were performed on colonic longitudinal smooth muscle strips (CLSMs) under isometric conditions.CLSMs suspended in tissue chambers were stimulated by KCl (80 mM) or acetylcholine (ACh,0.1 mM),or exhausting intracellular Ca2+ and intal flow of extracellular Ca2+ to induce muscle contraction and their responses to different doses of BPYX pill were observed.After that,incubation with different inhibitors was conducted to verify its underlying mechanism.Results:Bupi Yichang pill dose-dependently and reversibly inhibited colonic contraction.The antispasmodic effect of BPYC pill was partially blocked by 3,4,5-trimethoxybenzoic acid 8-(diethylamino)octyl ester hydrochloride (TMB-8,an intracellular Ca2+ antagonist,500 μM),thapsigargin (a non-competitive inhibitor of the sarco/endoplasmic reticulum Ca2+ ATPase,1 μM),and nifedipine (a voltage-dependent Ca2+ channel blocker,10 μM) (P ＜.05).However,there were no significant difference after incubation with ethylene glycol tetraacetic acid (EGTA,a calcium chelating agent,1 mM),4-aminopyridine (4-AP,a potassium channel blocker,50 μM),NG-nitro-L-arginine methyl ester (L-NAME,an inhibitor of nitric oxide synthase,10 mM),methylene blue (an inhibitor of cyclic guanosine monophosphate,10 μM) and apamin (a selectire blocker of Ca2+-activated K+ channel,0.1 μM) (P ＞.05).Conclusion:Bupi Yichang pill could inhibit colonic contraction of rats in vitro and its antispasmodic effect might be partially mediated by calcium channels.