AJP - Gastrointestinal and Liver Physiology, Vol 271, Issue 3 415-G422, Copyright © 1996 by American Physiological Society

ARTICLES

Transport of n-butyrate into human colonic luminal membrane vesicles

J. M. Harig, E. K. Ng, P. K. Dudeja, T. A. Brasitus and K. Ramaswamy
Department of Medicine, University of Illinois at Chicago, USA.

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.

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