Magnolol inhibits colonic motility through down-regulation of voltage-sensitive L-type Ca2+ channels of colonic smooth muscle cells in rats

This study aimed to investigate the effect of magnolol (5,5′-diallyl-2,2′-biphenyldiol) on contraction in distal colonic segments of rats and the underlying mechanisms. Colonic segments were mounted in organ baths for isometric force measurement. Whole-cell voltage-sensitive L-type Ca2+ currents were recorded on isolated single colonic smooth muscle cells using patch-clamp technique. The spontaneous contractions and acetylcholine (ACh)- and Bay K 8644-induced contractions were inhibited by magnolol (3–100μM). In the presence of Bay K8644 (100nM), magnolol (10–100μM) inhibited the contraction induced by 10μM ACh. By contrast, tetrodotoxin (100nM) and Nώ-nitro-l-arginine methyl ester (l-NAME 100μM) did not change the inhibitory effect of magnolol (10μM). In addition, magnolol (3–100μM) inhibited the L-type Ca2+ currents. The present results suggest that magnolol inhibits colonic smooth muscle contraction through downregulating L-type Ca2+ channel activity.