title: Characterisation of 5-HT3C, 5-HT3D and 5-HT3E receptor subunits: evolution, distribution and function.
abstract: The 5-HT(3) receptor is a member of the 'Cys-loop' family of ligand-gated ion channels that mediate fast excitatory and inhibitory transmission in the nervous system. Current evidence points towards native 5-HT(3) receptors originating from homomeric assemblies of 5-HT(3A) or heteromeric assembly of 5-HT(3A) and 5-HT(3B). Novel genes encoding 5-HT(3C), 5-HT(3D), and 5-HT(3E) have recently been described but the functional importance of these proteins is unknown. In the present study, in silico analysis (confirmed by partial cloning) indicated that 5-HT(3C), 5-HT(3D), and 5-HT(3E) are not human-specific as previously reported: they are conserved in multiple mammalian species but are absent in rodents. Expression profiles of the novel human genes indicated high levels in the gastrointestinal tract but also in the brain, Dorsal Root Ganglion (DRG) and other tissues. Following the demonstration that these subunits are expressed at the cell membrane, the functional properties of the recombinant human subunits were investigated using patch clamp electrophysiology. 5-HT(3C), 5-HT(3D), and 5-HT(3E) were all non-functional when expressed alone. Co-transfection studies to determine potential novel heteromeric receptor interactions with 5-HT(3A) demonstrated that the expression or function of the receptor was modified by 5-HT(3C) and 5-HT(3E), but not 5-HT(3D). The lack of distinct effects on current rectification, kinetics or pharmacology of 5-HT(3A) receptors does not however provide unequivocal evidence to support a direct contribution of 5-HT(3C) or 5-HT(3E) to the lining of the ion channel pore of novel heteromeric receptors. The functional and pharmacological contributions of these novel subunits to human biology and diseases such as irritable bowel syndrome for which 5-HT(3) receptor antagonists have major clinical usage, therefore remains to be fully determined.
authors.affiliation: Molecular Discovery Research, GlaxoSmithKline, Harlow, Essex, UK.
authors.forename: Joanna D
authors.initials: JD
authors.lastname: Holbrook
authors.forename: Catherine H
authors.initials: CH
authors.lastname: Gill
authors.forename: Noureddine
authors.initials: N
authors.lastname: Zebda
authors.forename: Jon P
authors.initials: JP
authors.lastname: Spencer
authors.forename: Rebecca
authors.initials: R
authors.lastname: Leyland
authors.forename: Kim H
authors.initials: KH
authors.lastname: Rance
authors.forename: Han
authors.initials: H
authors.lastname: Trinh
authors.forename: Gemma
authors.initials: G
authors.lastname: Balmer
authors.forename: Fiona M
authors.initials: FM
authors.lastname: Kelly
authors.forename: Shahnaz P
authors.initials: SP
authors.lastname: Yusaf
authors.forename: Nicola
authors.initials: N
authors.lastname: Courtenay
authors.forename: Jane
authors.initials: J
authors.lastname: Luck
authors.forename: Andrew
authors.initials: A
authors.lastname: Rhodes
authors.forename: Sundip
authors.initials: S
authors.lastname: Modha
authors.forename: Stephen E
authors.initials: SE
authors.lastname: Moore
authors.forename: Gareth J
authors.initials: GJ
authors.lastname: Sanger
authors.forename: Martin J
authors.initials: MJ
authors.lastname: Gunthorpe
mesh_terms: D000818:Animals; D005075:Biological Evolution; D002461:Cell Line, Transformed; D006224:Cricetinae; D003412:Cricetulus; D004305:Dose-Response Relationship, Drug; D004558:Electric Stimulation / Q000379:methods; D005289:Ferrets; D018756:GABA Antagonists / Q000494:pharmacology; D049452:Green Fluorescent Proteins / Q000235:genetics; D006801:Humans; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D018408:Patch-Clamp Techniques / Q000379:methods; D010852:Picrotoxin / Q000494:pharmacology; D021122:Protein Subunits / Q000502:physiology*; D011817:Rabbits; D044406:Receptors, Serotonin, 5-HT3 / Q000737:chemistry* / Q000502:physiology*; D012701:Serotonin / Q000494:pharmacology; D014162:Transfection
chemical_list: D018756:GABA Antagonists; D049452:Green Fluorescent Proteins; D010852:Picrotoxin; D021122:Protein Subunits; D044406:Receptors, Serotonin, 5-HT3; D012701:Serotonin