Mechanisms mediating serotonin-induced contraction of colonic myocytes.
1. 5-Hydroxytryptamine (5-HT) has an important role in the pathogenesis of irritable bowel syndrome. To investigate the effects of 5-HT on the contractile activity of myocytes of the guinea-pig proximal colon, cell imaging before and after contraction was undertaken and images were analysed using image-analysis software. Ion currents and membrane potentials were measured. Cytoplasmic free Ca(2+) was recorded using a confocal microscope following loading of the cells with the fluorescent probe Fura-2AM. 2. 5-Hydroxytryptamine reduced cell length in a dose-dependent manner (EC(50) = 0.189 micromol/L). Under current clamp, 10 micromol/L 5-HT reduced action potential amplitude (measured as peak height) and decreased action potential duration, as well as depolarizing the resting potential from -68.4 +/- 3.6 to -22.96 +/- 4.65 mV. Iberiotoxin (1 micromol/L) blocked the effects of 5-HT in reducing the time to repolarization (T(90)) and nicardipine (5 micromol/L) blocked the effects of 5-HT in reducing action potential amplitude. 3. In the whole-cell mode, 5-HT enhanced L-type Ca(2+) currents, large conductance K(+) channel (BK(Ca)) currents and spontaneous transient outward currents (STOC). In addition, 5-HT increased intracellular Ca(2+) levels. Ondansetron (10 micromol/L) blocked the effects of 5-HT in enhancing L-type Ca(2+) currents, BK(Ca) currents and STOC. 4. In conclusion, 5-HT induces contraction of colonic myocytes, mostly as a result of Ca(2+) release from the sarcoplasmic reticulum (SR) following activation of 5-HT(3) receptors and the inositol 1,4,5-trisphosphate pathway. In addition, the effect of 5-HT in decreasing action potential amplitude is mediated by the release of Ca(2+) from the SR, as well as by enhanced L-type Ca(2+) current. 5-Hydroxytryptamine decreased action potential duration by enhancing BK(Ca) current.
Xu
Long
L
Department of Gastroenterology, Renmin Hospital, Wuhan University, Wuhan, China.
Yu
Bao-Ping
BP
Chen
Jian-Guo
JG
Luo
He-Sheng
HS
D000818:Animals; D002118:Calcium / Q000502:physiology; D003106:Colon / Q000166:cytology / Q000502:physiology*; D005260:Female; D006168:Guinea Pigs; D066298:In Vitro Techniques; D008564:Membrane Potentials / Q000187:drug effects; D009119:Muscle Contraction / Q000187:drug effects; D032389:Myocytes, Smooth Muscle / Q000187:drug effects* / Q000502:physiology; D012701:Serotonin / Q000494:pharmacology*; D018490:Serotonin Agents / Q000494:pharmacology*
D018490:Serotonin Agents; D012701:Serotonin; D002118:Calcium