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 (3-100 mu M). In the presence of Bay K8644 (100 nM), magnolol (10-100 mu M) inhibited the contraction induced by 10 mu M ACh. By contrast, tetrodotoxin (100 nM) and N-omega-nitro-L-arginine methyl ester (L-NAME 100 mu M) did not change the inhibitory effect of magnolol (10 mu M). In addition, magnolol (3-100 mu M) inhibited the L-type Ca2+ currents. The present results suggest that magnolol inhibits colonic smooth muscle contraction through downregulating L-type Ca2+ channel activity. (C) 2013 Elsevier GmbH. All rights reserved.