Transport of n-butyrate into human colonic luminal membrane vesicles

• Published in: The American journal of physiology Vol. 271; no. 3; pp. G415 - G422
• Main Authors: Harig, J.M, Ng, E.K, Dudeja, P.K, Brasitus, T.A, Ramaswamy, K
• Format: Journal Article
• Language: English
• Published: United States 01.09.1996
• Subjects: Biological Transport; Butyrates - metabolism; Butyric Acid; Colon - metabolism; Colon - ultrastructure; Cytoplasmic Granules - metabolism; Humans; Hydrogen-Ion Concentration; short chain fatty acids
• ISSN: 0002-9513; 2163-5773
• DOI: 10.1152/ajpgi.1996.271.3.g415

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 Cl(-), 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.