title: Expression and membrane localization of MCT isoforms along the length of the human intestine.
abstract: Recent studies from our laboratory and others have demonstrated the involvement of monocarboxylate transporter (MCT)1 in the luminal uptake of short-chain fatty acids (SCFAs) in the human intestine. Functional studies from our laboratory previously demonstrated kinetically distinct SCFA transporters on the apical and basolateral membranes of human colonocytes. Although apical SCFA uptake is mediated by the MCT1 isoform, the molecular identity of the basolateral membrane SCFA transporter(s) and whether this transporter is encoded by another MCT isoform is not known. The present studies were designed to assess the expression and membrane localization of different MCT isoforms in human small intestine and colon. Immunoblotting was performed with the purified apical and basolateral membranes from human intestinal mucosa obtained from organ donor intestine. Immunohistochemistry studies were done on paraffin-embedded sections of human colonic biopsy samples. Immunoblotting studies detected a protein band of approximately 39 kDa for MCT1, predominantly in the apical membranes. The relative abundance of MCT1 mRNA and protein increased along the length of the human intestine. MCT4 (54 kDa) and MCT5 (54 kDa) isoforms showed basolateral localization and were highly expressed in the distal colon. Immunohistochemical studies confirmed that human MCT1 antibody labeling was confined to the apical membranes, whereas MCT5 antibody staining was restricted to the basolateral membranes of the colonocytes. We speculate that distinct MCT isoforms may be involved in SCFA transport across the apical or basolateral membranes in polarized colonic epithelial cells.
authors.affiliation: Section of Digestive Diseases and Nutrition, Department of Medicine, University of Illinois at Chicago, Medical Research Service (600/151), Jesse Brown Veterans Affairs Medical Center, 820 South Damen Ave., Chicago, Illinois 60612, USA.
authors.forename: Ravinder K
authors.initials: RK
authors.lastname: Gill
authors.forename: Seema
authors.initials: S
authors.lastname: Saksena
authors.forename: Waddah A
authors.initials: WA
authors.lastname: Alrefai
authors.forename: Zaheer
authors.initials: Z
authors.lastname: Sarwar
authors.forename: Jay L
authors.initials: JL
authors.lastname: Goldstein
authors.forename: Robert E
authors.initials: RE
authors.lastname: Carroll
authors.forename: Krishnamurthy
authors.initials: K
authors.lastname: Ramaswamy
authors.forename: Pradeep K
authors.initials: PK
authors.lastname: Dudeja
mesh_terms: D002462:Cell Membrane / Q000378:metabolism*; D015870:Gene Expression; D006801:Humans; D007413:Intestinal Mucosa / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism*; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism; D027981:Symporters / Q000378:metabolism*; D000099233:Monocarboxylate Transport Protein 1
chemical_list: D027501:Monocarboxylic Acid Transporters; D020033:Protein Isoforms; D012333:RNA, Messenger; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1