title: A novel role for TRPM8 in visceral afferent function.
abstract: Transient receptor potential ion channel melastatin subtype 8 (TRPM8) is activated by cold temperatures and cooling agents, such as menthol and icilin. Compounds containing peppermint are reported to reduce symptoms of bowel hypersensitivity; however, the underlying mechanisms of action are unclear. Here we determined the role of TRPM8 in colonic sensory pathways. Laser capture microdissection, quantitative reverse transcription-polymerase chain reaction (RT-PCR), immunofluorescence, and retrograde tracing were used to localise TRPM8 to colonic primary afferent neurons. In vitro extracellular single-fibre afferent recordings were used to determine the effect of TRPM8 channel activation on the chemosensory and mechanosensory function of colonic high-threshold afferent fibres. TRPM8 mRNA was present in colonic DRG neurons, whereas TRPM8 protein was present on nerve fibres throughout the wall of the colon. A subpopulation (24%, n=58) of splanchnic serosal and mesenteric afferents tested responded directly to icilin (5 μmol/L). Subsequently, icilin significantly desensitised afferents to mechanical stimulation (P<.0001; n=37). Of the splanchnic afferents responding to icilin, 21 (33%) also responded directly to the TRPV1 agonist capsaicin (3 μmol/L), and icilin reduced the direct chemosensory response to capsaicin. Icilin also prevented mechanosensory desensitization and sensitization induced by capsaicin and the TRPA1 agonist AITC (40 μmol/L), respectively. TRPM8 is present on a select population of colonic high threshold sensory neurons, which may also co-express TRPV1. TRPM8 couples to TRPV1 and TRPA1 to inhibit their downstream chemosensory and mechanosensory actions.
authors.affiliation: Nerve-Gut Research Laboratory, Department of Gastroenterology & Hepatology, Hanson Institute, Royal Adelaide Hospital, Adelaide, South Australia, Australia Discipline of Medicine, University of Adelaide, Adelaide, South Australia, Australia Discipline of Physiology, University of Adelaide, Adelaide, South Australia, Australia.
authors.forename: Andrea M
authors.initials: AM
authors.lastname: Harrington
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Hughes
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Martin
authors.forename: Jing
authors.initials: J
authors.lastname: Yang
authors.forename: Joel
authors.initials: J
authors.lastname: Castro
authors.forename: Nicole J
authors.initials: NJ
authors.lastname: Isaacs
authors.forename: Ashley L
authors.initials: AL
authors.lastname: Blackshaw
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Brierley
mesh_terms: D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000818:Animals; D015740:Calcitonin Gene-Related Peptide / Q000378:metabolism; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000378:metabolism; D003106:Colon / Q000294:innervation; D005456:Fluorescent Dyes / Q000378:metabolism; D005727:Ganglia, Spinal / Q000166:cytology; D015870:Gene Expression / Q000187:drug effects / Q000502:physiology*; D006930:Hyperalgesia / Q000235:genetics / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D042282:Microdissection / Q000379:methods; D011744:Pyrimidinones / Q000494:pharmacology; D011984:Sensory Receptor Cells / Q000378:metabolism; D050053:TRPM Cation Channels / Q000235:genetics / Q000378:metabolism*; D050916:TRPV Cation Channels / Q000172:deficiency / Q000378:metabolism; D017833:Visceral Afferents / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*
chemical_list: D005456:Fluorescent Dyes; D011744:Pyrimidinones; D050053:TRPM Cation Channels; C492297:TRPM8 protein, mouse; D050916:TRPV Cation Channels; C493921:TRPV1 protein, mouse; D002772:Cholera Toxin; C490483:icilin; D015740:Calcitonin Gene-Related Peptide