Contractile effects and intracellular Ca2+ signalling induced by emodin in circular smooth muscle cells of rat colon.
OBJECTIVE
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 Ca(2+) ([Ca(2+)]i) signalling was studied in smooth muscle cells using Ca(2+) 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 [Ca(2+)]i followed by a sustained elevation in [Ca(2+)]i. The emodin -induced increase in [Ca(2+)]i was unaffected by nifedipine, a voltage-gated Ca(2+)-channel antagonist, and the sustained phase of the rising of [Ca(2+)]i was attenuated by extracellular Ca(2+) removal with EGTA solution. Inhibiting Ca(2+) release from ryanodine-sensitive intracellular stores by ryanodine reduced the peak increase in [Ca(2+)]i. Using heparin, an antagonist of IP(3)R, almost abolished the peak increase in [Ca(2+)]i.


CONCLUSIONS
Emodin has a direct excitatory effect on circular smooth muscle cells in rat colon mediated via Ca(2+)/CaM dependent pathways. Furthermore, emodin-induced peak [Ca(2+)]i increase may be attributable to the Ca(2+) release from IP(3) sensitive stores, which further promote Ca(2+) release from ryanodine-sensitive stores through CICR mechanism. Additionally, Ca(2+) influx from extracellular medium contributes to the sustained increase in [Ca(2+)]i.
Ma
Tao
T
Department of Surgery, General Hospital of Tianjin Medical University, Tianjin 300052, China. mataoemail@yahoo.com.cn
Qi
Qing-Hui
QH
Yang
Wen-Xiu
WX
Xu
Jian
J
Dong
Zuo-Liang
ZL
D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects*; D003106:Colon / Q000187:drug effects / Q000502:physiology*; D004642:Emodin / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology*; D005769:Gastrointestinal Motility; D007425:Intracellular Membranes / Q000378:metabolism; D009130:Muscle, Smooth / Q000187:drug effects / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar
D004791:Enzyme Inhibitors; D004642:Emodin