title: Mercaptopropionate inhibits butyrate uptake in isolated apical membrane vesicles of the rat distal colon.
abstract: OBJECTIVE
  Previous observations have shown that mercapto- and bromo- short-chain fatty acids diminish fatty acid use in colonic epithelium. The aim of this study was to investigate whether this effect is attributable to the inhibition of short-chain fatty acid uptake.
  
  
  METHODS
  Apical membrane vesicles of rat colonocytes were prepared by a discontinuous sucrose gradient after isolation of membrane caps. [14C]butyrate uptake was measured by rapid filtration technique.
  
  
  RESULTS
  Preloading of isolated apical membrane vesicles with bicarbonate or butyrate stimulated [14C]butyrate uptake and resulted in up to fivefold overshoots. Increasing extravesicular butyrate concentrations saturated the bicarbonate-stimulated butyrate uptake with a binding constant of 44.7 +/- 5.9 mmol/L and a maximum velocity of 33.2 +/- 2.7 nmol.mg protein-1.3 s-1. Intravesicular butyrate uptake was inhibited by addition of 20 mmol/L 3-mercaptopropionate (43.0% +/- 5.6%), whereas 2-bromo-propionate (13.9% +/- 4.1%) and 4-bromobutyrate (22.6% +/- 5.3%) did not significantly alter butyrate uptake. Increasing concentrations of 3-mercaptopropionate had a competitive inhibitory effect on butyrate uptake with a binding constant following inhibition of 6.25 +/- 0.87 mmol/L and a maximum velocity of 5.82 +/- 1.01 nmol.mg protein-1.3 s-1.
  
  
  CONCLUSIONS
  Butyrate uptake in apical membrane vesicles of rat distal colon is mediated by a low-affinity anion transport system, which can be competitively inhibited by 3-mercaptopropionate but not by 2-bromopropionate and 4-bromobutyrate.
authors.affiliation: Second Department of Internal Medicine, Johann Wolfgang Goethe University, Frankfurt, Germany.
authors.forename: J
authors.initials: J
authors.lastname: Stein
authors.forename: O
authors.initials: O
authors.lastname: Schröder
authors.forename: V
authors.initials: V
authors.lastname: Milovic
authors.forename: W F
authors.initials: WF
authors.lastname: Caspary
mesh_terms: D015097:3-Mercaptopropionic Acid / Q000494:pharmacology*; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000494:pharmacology; D000818:Animals; D000838:Anions / Q000378:metabolism; D001639:Bicarbonates / Q000494:pharmacology; D001692:Biological Transport / Q000187:drug effects; D002087:Butyrates / Q000493:pharmacokinetics*; D020148:Butyric Acid; D002462:Cell Membrane / Q000378:metabolism*; D003106:Colon / Q000378:metabolism*; D005227:Fatty Acids / Q000378:metabolism / Q000494:pharmacology; D007474:Ion Exchange; D008297:Male; D051381:Rats; D017208:Rats, Wistar
chemical_list: D000838:Anions; D001639:Bicarbonates; D002087:Butyrates; D005227:Fatty Acids; D020148:Butyric Acid; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D015097:3-Mercaptopropionic Acid; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid