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[588] 5HT4 Receptor-Immunoreactivity (5HT4-IR) Is Expressed by Non-Neuronal Cells, Including Mast Cells, in Human, Rat and Mouse Gastrointestinal Tracts
CJ Streutker, EC Colley, K Hillsley, J Irvine, G Hicks, S Kelly, RH Stead. St. Michael
s Hospital, University of Toronto, Toronto, ON, Canada; Holburn Biomedical Corporation, Bowmanville, ON, Canada; Novartis Pharmaceuticals Canada, Dorval, QC, Canada
Background: 5HT4 agonists are pro-kinetic and used to treat patients with constipation and constipation-predominant IBS. Although studies describe the pharmacological actions of 5HT4 agonists on human GI samples, there is little data on the morphological localization of 5HT4 receptors in the gut.
Design: Samples of surgically derived tissue from the GI tract and mucosal biopsies from patients with various disorders were obtained with consent. These tissues and rat and mouse colons were formalin fixed. Immunohistochemistry was performed using polyclonal antisera specific for the 3rd cytoplasmic domain (LS655, LifeSpan, WA) and the C-terminus of the common sequence of the splice variants (NLS656, Novus, CO). In situ hybridization and double-stains of 5-HT4 with glial fibrillary acid protein, smooth muscle actin, GAP-43 and tryptase were done. Controls included 5HT4b-transfected CHO cells.
Results: Both antibodies labelled a small proportion of transfected CHO cells; however, NLS656 also stained wild type CHO cells, indicating a lack of specificity. 5HT4-IR was localized in the muscularis mucosa, muscularis propria and vessels by both antibodies in all human tissue samples. By in situ hybridization, muscle was also labeled. Significant neuronal staining was not identified; however, with NLS656 there appeared to be perineuronal staining in ganglia, consistent with the labeling of glial cells. Mast cells in all human, rat and mouse tissues were strongly LS655-IR positive and exhibited weak labeling with NLS656. Although not convincingly labeled in the resection samples, in mucosal biopsies enteroendocrine (EE) cells appeared to be 5HT4-IR.
Conclusions: The distribution of 5HT4 was consistent throughout the human GI tract, although the cellular localization varied depending upon the primary antiserum employed. The most consistent 5HT4-IR staining was on muscle cells, while neurons appeared to be negative. The labeling of mast cells in human, rat and mouse tissues, as well as EE cells, suggests that in addition to a direct action on muscle, 5HT4 ligands might act indirectly through these non-neuronal cell types. Results with NLS656 must be interpreted with caution because of the apparent lack of specificity.
Category: Gastrointestinal
Tuesday, March 27, 2007
Poster # 92, Tuesday Morning