Basic Research
Copyright ©The Author(s) 2003. Published by Baishideng Publishing Group Inc. All rights reserved.
World J Gastroenterol. Aug 15, 2003; 9(8): 1804-1807
Published online Aug 15, 2003. doi: 10.3748/wjg.v9.i8.1804
Contractile effects and intracellular Ca2+ signalling induced by emodin in circular smooth muscle cells of rat colon
Tao Ma, Qing-Hui Qi, Wen-Xiu Yang, Jian Xu, Zuo-Liang Dong
Tao Ma, Qing-Hui Qi, Jian Xu, Zuo-Liang Dong, Department of Surgery, General Hospital of Tianjin Medical University, Tianjin 300052, China
Wen-Xiu Yang, Division of Biophysics, Department of Physics, Nankai University, Tianjin 300071, China
Author contributions: All authors contributed equally to the work.
Supported by the National Natural Science Foundation of China, No.30171198
Correspondence to: Qing-Hui Qi, Department of Surgery, General Hospital of Tianjin Medical University, Tianjin 300052, China.
Telephone: +86-22-84283767
Received: January 11, 2003
Revised: January 16, 2003
Accepted: March 10, 2003
Published online: August 15, 2003

AIM: To investigate whether emodin has any effects on circular smooth muscle cells of rat colon and to examine the mechanism underlying its effect.

METHODS: Smooth muscle cells were isolated from the circular muscle layer of Wistar rat colon and the cell length was measured by computerized image micrometry. Intracellular Ca2+ ([Ca2+]i) signalling was studied in smooth muscle cells using Ca2+ indicator Fluo-3 AM on a laser-scanning confocal microscope.

RESULTS: Emodin dose-dependently induced smooth muscle cells contraction. The contractile responses induced by emodin were inhibited by preincubation of the cells with ML-7 (an inhibitor of MLCK). Emodin caused a large, transient increase in [Ca2+]i followed by a sustained elevation in [Ca2+]i. The emodin –induced increase in [Ca2+]i was unaffected by nifedipine, a voltage-gated Ca2+-channel antagonist, and the sustained phase of the rising of [Ca2+]i was attenuated by extracellular Ca2+ removal with EGTA solution. Inhibiting Ca2+ release from ryanodine-sensitive intracellular stores by ryanodine reduced the peak increase in [Ca2+]i. Using heparin, an antagonist of IP3R, almost abolished the peak increase in [Ca2+]i.

CONCLUSION: Emodin has a direct excitatory effect on circular smooth muscle cells in rat colon mediated via Ca2+/ CaM dependent pathways. Furthermore, emodin-induced peak [Ca2+]i increase may be attributable to the Ca2+ release from IP3 sensitive stores, which further promote Ca2+ release from ryanodine-sensitive stores through CICR mechanism. Additionally, Ca2+ influx from extracellular medium contributes to the sustained increase in [Ca2+]i.

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