Substrate and inhibitor specificity of butyrate uptake in apical membrane vesicles of the rat distal colon.
OBJECTIVE
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.
Schröder
O
O
Division of Gastroenterology, 2nd Department of Internal Medicine, Johann Wolfgang Goethe University, Frankfurt, Germany.
Opritz
J
J
Stein
J
J
D000818:Animals; D027321:Anion Transport Proteins; D017920:Antiporters / Q000494:pharmacology; D002087:Butyrates / Q000493:pharmacokinetics* / Q000494:pharmacology; D002352:Carrier Proteins / Q000494:pharmacology*; D003106:Colon / Q000166:cytology / Q000502:physiology*; D005232:Fatty Acids, Volatile / Q000493:pharmacokinetics*; D007408:Intestinal Absorption; D008297:Male; D051381:Rats; D017208:Rats, Wistar
D027321:Anion Transport Proteins; D017920:Antiporters; D002087:Butyrates; D002352:Carrier Proteins; D005232:Fatty Acids, Volatile