title: Acid sensing ion channels 2 and 3 are required for inhibition of visceral nociceptors by benzamil.
abstract: The Deg/ENaC family of ion channels, including ASIC1, 2 and 3, are candidate mechanotransducers in visceral and somatic sensory neurons, although each channel may play a different role in different sensory pathways. Here we determined which distinct populations of visceral sensory neurons are sensitive to the non-selective Deg/ENaC blocker benzamil, and which ASIC channels are targets for benzamil by studying its actions in knockout mice. Single afferent fiber recordings were made in vitro from mouse high threshold colonic thoracolumbar splanchnic afferents and low threshold gastroesophageal vagal afferents. mRNA expression of ASIC subtypes was compared between colonic and gastroesophageal afferents by quantitative RT-PCR of transcripts following laser capture microdissection of retrogradely labeled cell bodies. Mechanosensitivity of colonic afferents was potently reduced by benzamil (10(-6)-3 x 10(-4)M), whereas gastroesophageal afferents were marginally inhibited. Inhibition of colonic afferent mechanosensitivity by benzamil was markedly diminished in ASIC2-/- and ASIC3-/- mice, but unchanged in ASIC1a-/-. Therefore ASIC2 and 3 are targets for benzamil to inhibit colonic afferent mechanosensitivity. Conversely, gastroesophageal afferents are less sensitive to benzamil, and its action depends less on ASIC expression. mRNA for ASIC3 showed higher and ASIC1a showed lower relative expression in colonic afferents from thoracolumbar dorsal root ganglia than in gastric afferents from nodose (vagal) ganglia. These data indicate that ASICs on colonic afferents present distinct pharmacological targets for visceral pain.
authors.affiliation: Nerve-Gut Research Laboratory, Hanson Institute, Department of Gastroenterology, Hepatology and General Medicine, Royal Adelaide Hospital, Adelaide, SA 5000, Australia.
authors.forename: Amanda J
authors.initials: AJ
authors.lastname: Page
authors.forename: Stuart M
authors.initials: SM
authors.lastname: Brierley
authors.forename: Christopher M
authors.initials: CM
authors.lastname: Martin
authors.forename: Patrick A
authors.initials: PA
authors.lastname: Hughes
authors.forename: L Ashley
authors.initials: LA
authors.lastname: Blackshaw
mesh_terms: D062565:Acid Sensing Ion Channels; D000200:Action Potentials / Q000187:drug effects / Q000502:physiology; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D004305:Dose-Response Relationship, Drug; D005796:Genes / Q000187:drug effects; D066298:In Vitro Techniques; D008465:Mechanoreceptors / Q000187:drug effects* / Q000502:physiology; D008565:Membrane Proteins / Q000172:deficiency / Q000502:physiology*; D051379:Mice; D018345:Mice, Knockout; D009419:Nerve Tissue Proteins / Q000172:deficiency / Q000502:physiology*; D015222:Sodium Channels / Q000172:deficiency / Q000502:physiology*; D013153:Splanchnic Nerves / Q000187:drug effects / Q000502:physiology; D014630:Vagus Nerve / Q000187:drug effects / Q000502:physiology; D017833:Visceral Afferents / Q000187:drug effects* / Q000502:physiology
chemical_list: C568267:ASIC1 protein, mouse; C568265:ASIC2 protein, mouse; C508378:ASIC3 protein, mouse; D062565:Acid Sensing Ion Channels; D008565:Membrane Proteins; D009419:Nerve Tissue Proteins; D015222:Sodium Channels; C013407:benzamil; D000584:Amiloride