title: Distribution of 5-HT3, 5-HT4, and 5-HT7 Receptors Along the Human Colon.
abstract: OBJECTIVE
  Several disorders of the gastrointestinal tract are associated with abnormal serotonin (5-HT) signaling or metabolism where the 5-HT3 and 5-HT4 receptors are clinically relevant. The aim was to examine the distribution of 5-HT3, 5-HT4, and 5-HT7 receptors in the normal human colon and how this is associated with receptor interacting chaperone 3, G protein coupled receptor kin-ases, and protein LIN-7 homologs to extend previous observations limited to the sigmoid colon or the upper intestine.
  
  
  METHODS
  Samples from ascending, transverse, descending, and sigmoid human colon were dissected into 3 separate layers (mucosa, lon-gitudinal, and circular muscles) and ileum samples were dissected into mucosa and muscle layers (n = 20). Complementary DNA was synthesized by reverse transcription from extracted RNA and expression was determined by quantitative or end point polymerase chain reaction.
  
  
  RESULTS
  The 5-HT3 receptor subunits were found in all tissues throughout the colon and ileum. The A subunit was detected in all sam-ples and the C subunit was expressed at similar levels while the B subunit was expressed at lower levels and less frequently. The 5-HT3 receptor E subunit was mainly found in the mucosa layers. All splice variants of the 5-HT4 and 5-HT7 receptors were expressed throughout the colon although the 5-HT4 receptor d, g, and i variants were expressed less often.
  
  
  CONCLUSIONS
  The major differences in 5-HT receptor distribution within the human colon are in relation to the mucosa and muscular tissue layers where the 5-HT3 receptor E subunit is predominantly found in the mucosal layer which may be of therapeutic relevance.
authors.affiliation: Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville campus), Parkville Victoria, Australia.|Drug and Herbal Research Center, Faculty of Pharmacy, Universiti Kebangsaan Malaysia, Kuala Lumpur, Malaysia (Current address).
authors.forename: Nor S
authors.identifier: http://orcid.org/0000-0003-4726-1972
authors.initials: NS
authors.lastname: Yaakob
authors.affiliation: Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville campus), Parkville Victoria, Australia.|School of Biomedical Sciences, Charles Sturt University, Wagga Wagga, New South Wales, Australia (Current address).
authors.forename: Kenneth A
authors.identifier: http://orcid.org/0000-0002-7369-1880
authors.initials: KA
authors.lastname: Chinkwo
authors.affiliation: Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville campus), Parkville Victoria, Australia.
authors.forename: Navinisha
authors.identifier: http://orcid.org/0000-0002-3524-4385
authors.initials: N
authors.lastname: Chetty
authors.affiliation: Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville campus), Parkville Victoria, Australia.
authors.forename: Ian M
authors.initials: IM
authors.lastname: Coupar
authors.affiliation: Drug Discovery Biology, Monash Institute of Pharmaceutical Sciences, Monash University (Parkville campus), Parkville Victoria, Australia.
authors.forename: Helen R
authors.identifier: http://orcid.org/0000-0002-1514-0909
authors.initials: HR
authors.lastname: Irving
keywords: Colon; G protein coupled receptor kinases; Ileum; Receptors; serotonin