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-[C-14] butyrate uptake technique. Human colonic tissues were obtained from mucosal scrapings from organ donor proximal colons. Our results, consistent with the existence of a HCO3-/SCFA exchanger in these membranes, are summarized as follows: 1) n-[C-14] butyrate influx was significantly stimulated into the vesicles in the presence of an outwardly directed HCO3- and an inwardly directed pH gradient; 2) n-[C-14] butyrate uptake was markedly inhibited (similar to40%) 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 HCO3- and pH-gradient-driven n-[C-14] butyrate; 4) n-[C-14] butyrate uptake was saturable with a Km for butyrate of 17.5 +/- 4.5 mM and a V-max of 20.9 +/- 1.2 nmol.mg protein (-1).5 s(-1); 5) n-[C-14] butyrate influx into the vesicles demonstrated a trans-stimulation phenomenon; and 6) intravesicular or extravesicular Cl- did not alter the anion-stimulated n-[C-14] butyrate uptake. Our results indicate the presence of a carrier-mediated HCO3-/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.