title: Mast cell tryptase and proteinase-activated receptor 2 induce hyperexcitability of guinea-pig submucosal neurons.
abstract: Mast cells that are in close proximity to autonomic and enteric nerves release several mediators that cause neuronal hyperexcitability. This study examined whether mast cell tryptase evokes acute and long-term hyperexcitability in submucosal neurons from the guinea-pig ileum by activating proteinase-activated receptor 2 (PAR2) on these neurons. We detected the expression of PAR2 in the submucosal plexus using RT-PCR. Most submucosal neurons displayed PAR2 immunoreactivity, including those colocalizing VIP. Brief (minutes) application of selective PAR2 agonists, including trypsin, the activating peptide SL-NH2 and mast cell tryptase, evoked depolarizations of the submucosal neurons, as measured with intracellular recording techniques. The membrane potential returned to resting values following washout of agonists, but most neurons were hyperexcitable for the duration of recordings (> 30 min-hours) and exhibited an increased input resistance and amplitude of fast EPSPs. Trypsin, in the presence of soybean trypsin inhibitor, and the reverse sequence of the activating peptide (LR-NH2) had no effect on neuronal membrane potential or long-term excitability. Degranulation of mast cells in the presence of antagonists of established excitatory mast cell mediators (histamine, 5-HT, prostaglandins) also caused depolarization, and following washout of antigen, long-term excitation was observed. Mast cell degranulation resulted in the release of proteases, which desensitized neurons to other agonists of PAR2. Our results suggest that proteases from degranulated mast cells cleave PAR2 on submucosal neurons to cause acute and long-term hyperexcitability. This signalling pathway between immune cells and neurons is a previously unrecognized mechanism that could contribute to chronic alterations in visceral function.
authors.affiliation: Gastrointestinal Diseases Research Unit, Queen's University, Kingston, Ontario, Canada.
authors.forename: David E
authors.initials: DE
authors.lastname: Reed
authors.forename: Carlos
authors.initials: C
authors.lastname: Barajas-Lopez
authors.forename: Graeme
authors.initials: G
authors.lastname: Cottrell
authors.forename: Sara
authors.initials: S
authors.lastname: Velazquez-Rocha
authors.forename: Olivier
authors.initials: O
authors.lastname: Dery
authors.forename: Eileen F
authors.initials: EF
authors.lastname: Grady
authors.forename: Nigel W
authors.initials: NW
authors.lastname: Bunnett
authors.forename: Stephen J
authors.initials: SJ
authors.lastname: Vanner
mesh_terms: D000818:Animals; D015550:Cell Degranulation; D004594:Electrophysiology; D006168:Guinea Pigs; D007082:Ileum / Q000294:innervation; D007150:Immunohistochemistry; D007782:Lactoglobulins / Q000494:pharmacology; D008407:Mast Cells / Q000378:metabolism* / Q000502:physiology; D009474:Neurons / Q000187:drug effects / Q000502:physiology*; D009842:Oligopeptides / Q000494:pharmacology; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin / Q000819:agonists / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012697:Serine Endopeptidases / Q000378:metabolism*; D013368:Submucous Plexus / Q000166:cytology / Q000187:drug effects / Q000502:physiology*; D013569:Synapses / Q000187:drug effects / Q000502:physiology; D014018:Tissue Distribution; D014357:Trypsin / Q000494:pharmacology; D053802:Tryptases; D014660:Vasoactive Intestinal Peptide / Q000378:metabolism
chemical_list: D007782:Lactoglobulins; D009842:Oligopeptides; D044464:Receptor, PAR-2; D018179:Receptors, Thrombin; C112356:seryl-leucyl-isoleucyl-glycyl--arginyl-leucinamide; D014660:Vasoactive Intestinal Peptide; D012697:Serine Endopeptidases; D014357:Trypsin; D053802:Tryptases