Involvement of cholinergic nicotinic receptors in the menthol-induced gastric relaxation.

We have previously demonstrated that menthol reduces murine gastric tone in part through a neural mechanism, involving adrenergic pathways and reduction of ongoing release of acetylcholine from enteric nerves. In the present study we aimed to verify whether the gastric relaxation to menthol may be triggered by interaction with neural receptors or ionic channels proteins, such as transient receptor potential (TRP)-melastatin8 (TRPM8), TRP-ankyrin 1 (TRPA1), 5-hydroxytriptamine 3 (5-HT3) receptor or cholinergic nicotinic receptors. Spontaneous mechanical activity was detected in vitro as changes in intraluminal pressure from isolated mouse stomach. Menthol (0.3-30 mM) induced gastric relaxation which was not affected by 5-benzyloxytryptamine, a TRPM8 receptor antagonist, HC030031, a TRPA1 channel blocker. In addition, allylisothiocyanate, a TRPA1 agonist, but not (2S,5R)-2-Isopropyl-N-(4-methoxyphenyl)-5-methylcyclohexanecarboximide, a selective TRPM8 agonist, induced gastric relaxation. Genic expression of TRPA1, but not of TRPM8, was revealed in mouse stomach. Indeed, menthol-induced gastric relaxation was significantly reduced by hexamethonium, cholinergic nicotinic receptor antagonist. Menthol, at concentrations that failed to affect gastric tone, reduced the contraction induced by dimethylphenylpiperazinium, nicotinic receptor agonist. The joint application of hexamethonium and atropine, muscarinc receptor antagonist, or hexamethonium and phentholamine, α-adrenergic receptor antagonist, did not produce any additive reduction of the relaxant response to menthol. Lastly, ondansetron, a 5-HT3 receptor antagonist, was ineffective. In conclusion, our study suggests that nicotinic receptors, but not TRP and 5-HT3 receptors, are molecular targets for menthol inducing murine gastric relaxation, ultimately due to the reduction of acetylcholine release from enteric nerves.

Amato A ，Serio R ，Mulè F 《-》

Contractile effect of TRPA1 receptor agonists in the isolated mouse intestine.

Penuelas A ，Tashima K ，Tsuchiya S ，Matsumoto K ，Nakamura T ，Horie S ，Yano S ... -  《EUROPEAN JOURNAL OF PHARMACOLOGY》

Tetrodotoxin-dependent effects of menthol on mouse gastric motor function.

Menthol, the main active constituent of peppermint oil, exerts gut spasmolytic effects, although its mechanism of action remains unclear. We investigated the effects of menthol on gastric emptying and spontaneous- or evoked- mechanical activity of whole murine stomach. Gastric emptying was calculated after i.p. administration of menthol (50mg/Kg). Responses induced by menthol on gastric intraluminal pressure and evoked-cholinergic contractions were analyzed in vitro. Menthol decreased the gastric emptying rate. In vitro, menthol (0.3-30 mM) produced a concentration-dependent relaxation of whole stomach, that was significantly reduced by tetrodotoxin or ω-conotoxin GVIA. The gastric relaxant responses were not affected by Nω-nitro-L-arginine methyl ester, inhibitor of nitric oxide-synthase, apamin or [Lys1,Pro2,5,Arg3,4,Tyr6] vasoactive intestinal peptide (VIP)(7-28), a VIP receptor antagonist, but they were significantly antagonized by atropine or guanethidine, a blocker of adrenergic neurotransmission. The joint application of atropine and guanethidine did not produce any additive effects on menthol effects. Phentolamine, an α-adrenoceptor antagonist, but not propranolol, a β-adrenoceptor antagonist, significantly reduced menthol responses and the contemporary administration of both adrenergic antagonists did not produce additive effects. Menthol (1-100 μM) produced a reduction of the electrically-evoked cholinergic contractions, which was prevented by guanethidine. Menthol did not affect the contractions induced by carbachol. In conclusion, menthol in mouse, is able to reduce the rate of gastric emptying and to relax the stomach in vitro. The latter effect appears due, almost in part, to neural mechanisms, with involvement of α-adrenoceptors leading to reduction of tonic ongoing release of acetylcholine.

Amato A ，Baldassano S ，Serio R ，Mulè F ... -  《-》

Differential Contribution of TRPA1, TRPV4 and TRPM8 to Colonic Nociception in Mice.

Mueller-Tribbensee SM ，Karna M ，Khalil M ，Neurath MF ，Reeh PW ，Engel MA ... -  《PLoS One》

Human dental pulp fibroblasts express the "cold-sensing" transient receptor potential channels TRPA1 and TRPM8.

Transient receptor potential (TRP) channels comprise a group of nonselective calcium-permeable cationic channels, which are polymodal sensors of environmental stimuli such as thermal changes and chemicals. TRPM8 and TRPA1 are cold-sensing TRP channels activated by moderate cooling and noxious cold temperatures, respectively. Both receptors have been identified in trigeminal ganglion neurones, and their expression in nonneuronal cells is now the focus of much interest. The aim of this study was to investigate the molecular and functional expression of TRPA1 and TRPM8 in dental pulp fibroblasts. Human dental pulp fibroblasts were derived from healthy molar teeth. Gene and protein expression was determined by polymerase chain reaction and Western blotting. Cellular localization was investigated by immunohistochemistry, and TRP functionality was determined by Ca(2+) microfluorimetry. Polymerase chain reaction and Western blotting showed gene and protein expression of both TRPA1 and TRPM8 in fibroblast cells in culture. Immunohistochemistry studies showed that TRPA1 and TRPM8 immunoreactivity co-localized with the human fibroblast surface protein. In Ca(2+) microfluorimetry studies designed to determine the functionality of TRPA1 and TRPM8 in pulp fibroblasts, we showed increased intracellular calcium ([Ca(2+)](i)) in response to the TRPM8 agonist menthol, the TRPA1 agonist cinnamaldehyde, and to cool and noxious cold stimuli, respectively. The responses to agonists and thermal stimuli were blocked in the presence of specific TRPA1 and TRPM8 antagonists. Human dental pulp fibroblasts express TRPA1 and TRPM8 at the molecular, protein, and functional levels, indicating a possible role for fibroblasts in mediating cold responses in human teeth.

El Karim IA ，Linden GJ ，Curtis TM ，About I ，McGahon MK ，Irwin CR ，Killough SA ，Lundy FT ... -  《-》