Mechanism of n-butyrate uptake in the human proximal colonic basolateral membranes.
Current studies were undertaken to characterize the mechanism of short-chain fatty acid (SCFA) transport in isolated human proximal colonic basolateral membrane vesicles (BLMV) utilizing a rapid-filtration n-[(14)C]butyrate uptake technique. Human colonic tissues were obtained from mucosal scrapings from organ donor proximal colons. Our results, consistent with the existence of a HCO(3)(-)/SCFA exchanger in these membranes, are summarized as follows: 1) n-[(14)C]butyrate influx was significantly stimulated into the vesicles in the presence of an outwardly directed HCO(3)(-) and an inwardly directed pH gradient; 2) n-[(14)C]butyrate uptake was markedly inhibited (approximately 40%) by anion exchange inhibitor niflumic acid (1 mM), but SITS and DIDS (5 mM) had no effect; 3) structural analogs e.g., acetate and propionate, significantly inhibited uptake of HCO(3)(-) and pH-gradient-driven n-[(14)C]butyrate; 4) n-[(14)C]butyrate uptake was saturable with a K(m) for butyrate of 17.5 +/- 4.5 mM and a V(max) of 20.9 +/- 1.2 nmol x mg protein(-1) x 5 s(-1); 5) n-[(14)C]butyrate influx into the vesicles demonstrated a transstimulation phenomenon; and 6) intravesicular or extravesicular Cl(-) did not alter the anion-stimulated n-[(14)C]butyrate uptake. Our results indicate the presence of a carrier-mediated HCO(3)(-)/SCFA exchanger on the human colonic basolateral membrane, which appears to be distinct from the previously described anion exchangers in the membranes of colonic epithelia.
Tyagi
S
S
Department of Medicine, University of Illinois at Chicago and Westside Veterans Administration Medical Center, Chicago, Illinois 60612, USA.
Venugopalakrishnan
J
J
Ramaswamy
K
K
Dudeja
P K
PK
D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000085:Acetates / Q000494:pharmacology; D000328:Adult; D000584:Amiloride / Q000494:pharmacology; D000838:Anions; D001639:Bicarbonates / Q000378:metabolism / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002087:Butyrates / Q000378:metabolism*; D002250:Carbon Radioisotopes; D002462:Cell Membrane / Q000378:metabolism*; D002712:Chlorides / Q000008:administration & dosage / Q000494:pharmacology; D003106:Colon / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism; D007700:Kinetics; D008564:Membrane Potentials; D009544:Niflumic Acid / Q000494:pharmacology; D011422:Propionates / Q000494:pharmacology
D000085:Acetates; D000838:Anions; D001639:Bicarbonates; D002087:Butyrates; D002250:Carbon Radioisotopes; D002712:Chlorides; D011422:Propionates; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D009544:Niflumic Acid; D000584:Amiloride; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid