title: Transport of n-butyrate into human colonic luminal membrane vesicles.
abstract: Human colonic short-chain fatty acid (SCFA) absorption is associated with increased luminal pH and HCO3- and enhanced Na+ absorption. Therefore, the mechanism of colonic SCFA transport, its dependence on Na+ and HCO3- and interactions with Cl-/HCO3- and Na+/H+ exchangers were characterized. Luminal membrane vesicles (LMV) isolated by divalent cation precipitation from organ donor colons were used for n-butyrate transport. Uptake of n-butyrate into the human colonic LMV was minimal even in the presence of an inward pH gradient, but an outward HCO3- gradient significantly increased uptake rates. HCO3(-)-stimulated butyrate uptake was saturable with an apparent Michaelis constant of 1.5 +/- 0.2 mM and maximal velocity of 105 +/- 3 nmol.mg protein-1.3 s-1. Intravesicular butyrate resulted in trans-stimulation of n-[1-14C]butyrate uptake. Butyrate uptake was inhibited approximately 25-40% by C2-C5 SCFAs and approximately 40% by niflumic acid. Butyrate uptake was not affected by extravesicular Na+, and 22Na uptake was unaltered by extravesicular butyrate. Butyrate uptake was independent of extra- or intravesicular CI-, and butyrate loading produced no changes in 36Cl uptake. We conclude that the predominant mechanism of n-butyrate transport across the human colonic luminal membrane appears to be via a HCO3-/SCFA antiport system independent of Cl-/HCO3- exchange and Na+ transport.
authors.affiliation: Department of Medicine, University of Illinois at Chicago, USA.
authors.forename: J M
authors.initials: JM
authors.lastname: Harig
authors.forename: E K
authors.initials: EK
authors.lastname: Ng
authors.forename: P K
authors.initials: PK
authors.lastname: Dudeja
authors.forename: T A
authors.initials: TA
authors.lastname: Brasitus
authors.forename: K
authors.initials: K
authors.lastname: Ramaswamy
mesh_terms: D001692:Biological Transport; D002087:Butyrates / Q000378:metabolism*; D020148:Butyric Acid; D003106:Colon / Q000378:metabolism* / Q000648:ultrastructure; D003594:Cytoplasmic Granules / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration
chemical_list: D002087:Butyrates; D020148:Butyric Acid