Transport of n-butyrate into human colonic luminal membrane vesicles. Harig, James M., Edmond K. Ng, Pradeep K. Dudeja, Thomas A. Brasitus, and Krishnamurthy Ramaswamy. Departments of Medicine, University of Illinois at Chicago, West Side Veterans Administration Medical Center and University of Chicago
APStracts 3:0018G, 1996.
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. Bicarbonate-stimulated butyrate uptake was saturable with apparent Km = 1.5 +/- 0.2 ( mM) and Vmax = 105 +/- 3 (nmoles/mg protein/3sec). Intravesicular butyrate resulted in trans-stimulation of [1-14C] -butyrate uptake. Butyrate uptake was inhibited 25-40% by C2-C5 SCFAs and 40% by niflumic acid. Butyrate uptake was unaffected by extravesicular Na+, and [22Na] uptake was unaltered by extravesicular butyrate. Butyrate uptake was independent of extra- or intravesicular chloride, and butyrate loading produced no changes in [36Cl] uptake. Conclusions: 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 of sodium transport. 

Received 14 August 1995; accepted in final form 4 January 1996.
APS Manuscript Number G353-5.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 25 January 96