title: Voltage-gated ion channel Nav1.7 innervation in patients with idiopathic rectal hypersensitivity and paroxysmal extreme pain disorder (familial rectal pain).
abstract: Faecal urgency and incontinence with rectal hypersensitivity is a chronic, unexplained condition that is difficult to treat. The aim of this study was to determine if there was an altered level of the voltage gated tetrodotoxin-sensitive (TTX-s) sodium channel Na(v)1.7 in rectal sensory fibres, since this channel has been implicated in clinical nociceptive disorders. Full thickness rectal biopsies from patients with physiologically characterised rectal hypersensitivity (n=7) were compared with control tissues (n=10). Formalin fixed specimens were studied by immunohistochemistry using affinity purified antibodies to Na(v)1.7 and the pan-neuronal structural marker PGP9.5, and the immunoreactive nerve fibres quantified by computerised image analysis. In rectal hypersensitivity, Na(v)1.7 immunoreactive nerve fibres were significantly increased in mucosal (P=0.0004), sub-mucosal (P=0.019), and muscle layers (P=0.0076), while PGP9.5 immunoreactive nerve fibres were increased significantly only in the mucosa (P=0.04); ratios of Na(v)1.7:PGP9.5 showed a significant increase in all layers, suggesting increased expression of Na(v)1.7, and nerve sprouting in the mucosa. The cause of this increase remains uncertain, but may be due to increase of nerve growth factor (NGF), which regulates the expression of both Na(v)1.7 and TRPV1, which we have previously reported to be increased in this condition. In paroxysmal extreme pain disorder (familial rectal pain), where the gene that encodes Na(v)1.7 is mutated, Na(v)1.7 protein was undetectable in the rectum (n=2), which suggests reduced Na(v)1.7 immunoreactivity or expression. Drugs that target Na(v)1.7-expressing nerve terminals may be useful for treating rectal hypersensitivity, and combining these with TRPV1 antagonists may enhance efficacy.
authors.affiliation: Peripheral Neuropathy Unit, Imperial College London, Hammersmith Hospital, London, UK.
authors.forename: Yiangos
authors.initials: Y
authors.lastname: Yiangou
authors.forename: Paul
authors.initials: P
authors.lastname: Facer
authors.forename: Iain P
authors.initials: IP
authors.lastname: Chessell
authors.forename: Chas
authors.initials: C
authors.lastname: Bountra
authors.forename: Chris
authors.initials: C
authors.lastname: Chan
authors.forename: Caroline
authors.initials: C
authors.lastname: Fertleman
authors.forename: Virpi
authors.initials: V
authors.lastname: Smith
authors.forename: Praveen
authors.initials: P
authors.lastname: Anand
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D001706:Biopsy; D005242:Fecal Incontinence / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology; D005260:Female; D006801:Humans; D007150:Immunohistochemistry; D008297:Male; D008875:Middle Aged; D009154:Mutation; D062556:NAV1.7 Voltage-Gated Sodium Channel; D009412:Nerve Fibers / Q000378:metabolism; D009475:Neurons, Afferent / Q000378:metabolism / Q000473:pathology; D012007:Rectum / Q000294:innervation* / Q000378:metabolism* / Q000473:pathology; D015222:Sodium Channels / Q000235:genetics / Q000378:metabolism*; D013001:Somatoform Disorders / Q000378:metabolism* / Q000473:pathology / Q000503:physiopathology
chemical_list: D062556:NAV1.7 Voltage-Gated Sodium Channel; C486866:SCN9A protein, human; D015222:Sodium Channels