Berberine Depresses Contraction of Smooth Muscle via Inhibiting Myosin Light-chain Kinase

BACKGROUND: Berberine is a natural isoquinoline alkaloid possessing various pharmacological effects, particularly apparent in the treatment of diarrhea, but the underlying mechanism remains unclear. Smooth muscle myosin light-chain kinase (MLCK) plays a crucial role in the smooth muscle relaxation-contraction events, and it is well known that berberine can effectively depress the contraction of smooth muscle. Hence, whether berberine could inhibit MLCK and then depress the smooth muscle contractility might be researched. OBJECTIVE: The purpose of this study is to investigate the effects of berberine on MLCK. Based on this, the contractility of gastro-intestine, catalysis activity of MLCK, and molecular docking are going to be evaluated. MATERIALS AND METHODS: The experiment of smooth muscle contraction was directly monitored the contractions of the isolated gastrointestine by frequency and amplitude at different concentration of berberine. The effects of berberine on MLCK were measured in the presence of Ca(2+)-calmodulin, using the activities of 20 kDa myosin light chain (MLC(20)) phosphorylation, and myosin Mg(2+)-ATPase induced by MLCK. The docking study was conducted with expert software in the meantime. RESULTS: The phosphorylation of myosin and the Mg(2+)-ATPase activity is reduced in the presence of berberine. Moreover, berberine could inhibit the contractibility of isolated gastric intestine smooth muscle. Berberine could bind to the ATP binding site of MLCK through hydrophobic effect and hydrogen bonding according to the docking study. CONCLUSION: The present work gives a deep insight into the molecular mechanism for the treatment of diarrhea with berberine, i.e., berberine could suppress the contractility of smooth muscle through binding to MLCK and depressing the catalysis activity of MLCK. SUMMARY: Berberine significantly reduced the amplitude of contraction in isolated duodenum and gastric strips in rats. Berberine inhibited the phosphorylated extents of MLC20 and Mg2+-ATPase activity of phosphorylated myosin induced by MLCK. Berberine binds to the ATP binding site of MLCK by hydrophobic effect and hydrogen bonding. Berberine may modulate contraction of smooth muscle by inhibiting MLCK. Abbreviations used: MLCK: Myosin light chain kinase; MLC(20): 20 KDa regulating myosin light chain; CaM: Calmodulin.