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[Signal transduction of serotonin release from enterochromaffin cells in mouse ileal crypts]
M Hirafuji1, K Kato, T Suzuguchi
1Department of Pharmacology, Faculty of Pharmaceutical Sciences, Health Sciences University of Hokkaido, Ishikari-Tobetsu, Japan.
Abstract:
Although serotonin (5-HT) release from enterochromaffin (EC) cells is considered to be regulated by multiple receptor-mediated mechanisms, little is known about the signal transduction in EC cells. We investigated the effects of adrenoceptor stimulation on 5-HT release from ileal tissue and intracellular calcium dynamics of epithelial cells in isolated ileal crypts in mice. Ileal tissues placed in organ bath were perfused with a buffered solution. Released 5-HT was measured using HPLC-ECD. Ileal crypts were isolated by collagenase digestion followed by moderate pipetting. Intracellular calcium dynamics were analyzed by digital video-imaging system using fura-2. NE, but not isoprenaline (Iso), induced 5-HT release from mouse ileal tissue. NE-induced 5-HT release was antagonized by yohimbine and rauwolscine, but not by prazosin and bunazosin. NE, but not Iso, also elicited a transient elevation of intracellular calcium in some EC cells. The effect of NE (1 microM) was slightly suppressed by prazosin and bunazosin, but was remarkably suppressed by yohimbine and rauwolscine. UK 14,304 and Clonidine at 10 microM significantly induced an increase in intracellular calcium concentration. NE-induced intracellular calcium dynamics was not significantly affected by timolol, Ro20-1724, rolipram and 8-bromo-cAMP. These results suggest that NE-induced 5-HT release from ileal EC cells is mediated predominantly via alpha 2-, but not beta-adrenoceptors, by a mechanism dependent on elevation of intracellular calcium concentration.
Insights
Norepinephrine (NE) stimulates serotonin (5-HT) release from mouse ileal enterochromaffin (EC) cells primarily through alpha 2-adrenoceptors. This process involves an increase in intracellular calcium, highlighting a key signaling pathway in EC cells.
Area of Science:
- Gastroenterology
- Neuroscience
- Cell Biology
Background:
- Serotonin (5-HT) release from enterochromaffin (EC) cells is crucial for gut function.
- Signal transduction pathways in EC cells remain incompletely understood.
- Adrenoceptor involvement in 5-HT release is a significant area of investigation.
Purpose of the Study:
- To investigate the role of adrenoceptor stimulation in regulating 5-HT release from mouse ileal EC cells.
- To elucidate the intracellular calcium dynamics involved in NE-mediated 5-HT release.
- To identify the specific adrenoceptor subtypes involved in this signaling pathway.
Main Methods:
- Perfusion of mouse ileal tissue in an organ bath with subsequent 5-HT measurement via HPLC-ECD.
- Isolation of ileal crypts for analysis of intracellular calcium dynamics using fura-2 and digital video-imaging.
- Pharmacological characterization using various adrenoceptor agonists and antagonists.
Main Results:
- Norepinephrine (NE), but not isoprenaline (Iso), induced 5-HT release and intracellular calcium elevation in EC cells.
- NE-induced effects were predominantly antagonized by alpha 2-adrenoceptor blockers (yohimbine, rauwolscine).
- Specific alpha 2-agonists (UK 14,304, Clonidine) increased intracellular calcium, confirming alpha 2-adrenoceptor mediation.
Conclusions:
- NE-induced 5-HT release from ileal EC cells is primarily mediated by alpha 2-adrenoceptors.
- The signaling mechanism involves a calcium-dependent pathway.
- This study clarifies a critical adrenoceptor-mediated pathway regulating gut serotonin release.