title: Characterization of butyrate transport across the luminal membranes of equine large intestine.
abstract: The diet of the horse, pasture forage (grass), is fermented by the equine colonic microbiota to short-chain fatty acids, notably acetate, propionate and butyrate. Short-chain fatty acids provide a major source of energy for the horse and contribute to many vital physiological processes. We aimed to determine both the mechanism of butyrate uptake across the luminal membrane of equine colon and the nature of the protein involved. To this end, we isolated equine colonic luminal membrane vesicles. The abundance and activity of cysteine-sensitive alkaline phosphatase and villin, intestinal luminal membrane markers, were significantly enriched in membrane vesicles compared with the original homogenates. In contrast, the abundance of GLUT2 protein and the activity of Na(+)-K(+)-ATPase, known markers of the intestinal basolateral membrane, were hardly detectable. We demonstrated, by immunohistochemistry, that monocarboxylate transporter 1 (MCT1) protein is expressed on the luminal membrane of equine colonocytes. We showed that butyrate transport into luminal membrane vesicles is energized by a pH gradient (out < in) and is not Na(+) dependent. Moreover, butyrate uptake is time and concentration dependent, with a Michaelis-Menten constant of 5.6 ± 0.45 mm and maximal velocity of 614 ± 55 pmol s(-1) (mg protein)(-1). Butyrate transport is significantly inhibited by p-chloromercuribenzoate, phloretin and α-cyano-4-hydroxycinnamic acid, all potent inhibitors of MCT1. Moreover, acetate and propionate, as well as the monocarboxylates pyruvate and lactate, also inhibit butyrate uptake. Data presented here support the conclusion that transport of butyrate across the equine colonic luminal membrane is predominantly accomplished by MCT1.
authors.affiliation: Epithelial Function and Development Group, Department of Functional and Comparative Genomics, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK.
authors.forename: Taoufik
authors.initials: T
authors.lastname: Nedjadi
authors.affiliation: Epithelial Function and Development Group, Department of Functional and Comparative Genomics, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK.
authors.forename: Andrew W
authors.initials: AW
authors.lastname: Moran
authors.affiliation: Epithelial Function and Development Group, Department of Functional and Comparative Genomics, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK.
authors.forename: Miran A
authors.initials: MA
authors.lastname: Al-Rammahi
authors.affiliation: Epithelial Function and Development Group, Department of Functional and Comparative Genomics, Institute of Integrative Biology, University of Liverpool, Liverpool, L69 7ZB, UK spsb@liverpool.ac.uk.
authors.forename: Soraya P
authors.initials: SP
authors.lastname: Shirazi-Beechey
mesh_terms: D000818:Animals; D001692:Biological Transport; D002087:Butyrates / Q000493:pharmacokinetics*; D002462:Cell Membrane / Q000378:metabolism; D003106:Colon / Q000187:drug effects / Q000378:metabolism*; D051273:Glucose Transporter Type 2 / Q000378:metabolism; D006736:Horses; D006801:Humans; D007413:Intestinal Mucosa / Q000187:drug effects / Q000378:metabolism*; D007420:Intestine, Large / Q000187:drug effects / Q000378:metabolism*; D027501:Monocarboxylic Acid Transporters / Q000378:metabolism; D027981:Symporters / Q000378:metabolism; D000099233:Monocarboxylate Transport Protein 1
chemical_list: D002087:Butyrates; D051273:Glucose Transporter Type 2; D027501:Monocarboxylic Acid Transporters; D027981:Symporters; D000099233:Monocarboxylate Transport Protein 1