title: Basolateral glycylsarcosine (Gly-Sar) transport in Caco-2 cell monolayers is pH dependent.
abstract: OBJECTIVE
  Transepithelial di/tripeptide transport in enterocytes occurs via the apical proton-coupled peptide transporter, hPEPT1 (SLC15A1) and a basolateral peptide transporter, which has only been characterized functionally. In this study we examined the pH dependency, substrate uptake kinetics and substrate specificity of the transporter.
  
  
  METHODS
  We studied the uptake of [(14) C]Gly-Sar from basolateral solution into Caco-2 cell monolayers grown for 17-22 days on permeable supports, at a range of basolateral pH values.
  
  
  RESULTS
  Basolateral Gly-Sar uptake was pH dependent, with a maximal uptake rate at a basolateral pH of 5.5. Uptake of Gly-Sar decreased in the presence of the protonophore nigericin, indicating that the uptake was proton-coupled. The uptake was saturable, with a maximal flux (Vmax ) of 408 ± 71, 307 ± 25 and 188 ± 19 pmol/cm(2) /min (mean ± S.E., n = 3) at basolateral pH 5.0, 6.0 and 7.4, respectively. The compounds Gly-Asp, Glu-Phe-Tyr, Gly-Glu-Gly, Gly-Phe-Gly, lidocaine and, to a smaller degree, para-aminohippuric acid were all shown to inhibit the basolateral uptake of Gly-Sar.
  
  
  CONCLUSIONS
  The study showed that basolateral Gly-Sar transport in the intestinal cell line Caco-2 is proton-coupled. The inhibitor profile indicated that the transporter has broad substrate specificity.
authors.affiliation: Department of Pharmacy, The Faculty of Health and Medical Sciences, University of Copenhagen, Copenhagen, Denmark.
authors.forename: Ragna
authors.initials: R
authors.lastname: Berthelsen
authors.forename: Carsten Uhd
authors.initials: CU
authors.lastname: Nielsen
authors.forename: Birger
authors.initials: B
authors.lastname: Brodin
mesh_terms: D001692:Biological Transport; D018938:Caco-2 Cells; D004151:Dipeptides / Q000378:metabolism*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007413:Intestinal Mucosa / Q000378:metabolism*; D026901:Membrane Transport Proteins / Q000378:metabolism*; D009550:Nigericin / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D004151:Dipeptides; D026901:Membrane Transport Proteins; C004194:glycylsarcosine; D009550:Nigericin