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  • Title: Substrate and inhibitor specificity of butyrate uptake in apical membrane vesicles of the rat distal colon.
    Author: Schröder O, Opritz J, Stein J.
    Journal: Digestion; 2000; 62(2-3):152-8. PubMed ID: 11025362.
    Abstract:
    BACKGROUND/AIMS: There is substantial evidence that transcellular flux of short-chain fatty acid (SCFA) absorption, at least in part, is mediated by an anion exchange process with bicarbonate. METHODS: This anion exchange system was further characterized in apical membrane vesicles of the rat distal colon by studying substrate and inhibitor specificities of a variety of substituted monocarboxylic acids as well as of known inhibitors of the recently described monocarboxylate transporter MCT1 and MCT2. RESULTS: SCFA transport was significantly reduced in the presence of branched and unbranched SCFAs and several bromo, chloro and mercapto analogues as well as nicotinic acid and L-lactate. In contrast, known inhibitors of monocarboxylate transporter proteins like stilbene derivatives, phloretin and 2-cyano-4-hydroxycinnamate did not inhibit bicarbonate-gradient stimulated butyrate transport. Kinetic analysis of increasing substrate concentrations of 3-mercaptopropionate, L-lactate and nicotinic acid showed saturation kinetics with apparent K(i) of 6.1, 18.3 and 14.7 mmol/l, respectively. CONCLUSIONS: The data not only confirm earlier results that absorption of SCFAs in apical membranes of the rat distal colon is mediated by a relatively low affinity/high capacity SCFA(-)/HCO(-)(3) exchange mechanism, but also indicate that although this anion transporter shares some functional similarities, is not identical with the recently cloned MCT isoforms.
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