title: Characterization of the transport of uracil across Caco-2 and LLC-PK1 cell monolayers.
abstract: OBJECTIVE
  The purpose of this study was to characterize the transport of uracil, a pyrimidine nucleobase, in Caco-2 and LLC-PK, cells.
  
  
  METHODS
  Caco-2 and LLC-PK1 cells were grown to confluency on a permeable polycarbonate membrane insert to permit transport and uptake experiments after the loading of uracil on either the apical or basolateral side.
  
  
  RESULTS
  The vectorial transport of uracil in both directions was saturable with comparable Km and Vmax in Caco-2 cell monolayers, probably because of a Na+-independent transport system located on the basolateral membrane. In LLC-PK1 cell monolayers, two distinct transport systems, namely a Na+-dependent and a Na+-independent, were functional in the apical to basolateral (A-B) transport of uracil. The first system was saturable with a Km value of 3.67 +/- 0.40 microM, a Vmax of 11.31 +/- 0.91 pmol/cm2/min, and a Na+:uracil coupling stoichiometry of 1.28 +/- 0.20. The second system was Na+ independent and satuable with a low affinity (Km, 50.37 +/- 9.61 microM) and Vmax (16.01 +/- 4.48 pmol/cm2/min). The two transport systems appeared to be located on the apical membrane.
  
  
  CONCLUSIONS
  The mechanism of uracil transport differs depending on cell lines; a Na+-independent system on the basolateral membrane in Caco-2 cells and both Na+-dependent and Na+-independent systems on the apical membrane in LLC-PK1 cells seem to be responsible for the difference.
authors.affiliation: Department of Pharmaceutics, College of Pharmacy, Seoul National University, Kwanak-Gu, Korea.
authors.forename: Hong
authors.initials: H
authors.lastname: Li
authors.forename: Suk-Jae
authors.initials: SJ
authors.lastname: Chung
authors.forename: Chang-Koo
authors.initials: CK
authors.lastname: Shim
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000502:physiology; D018938:Caco-2 Cells; D002462:Cell Membrane / Q000378:metabolism; D006801:Humans; D018374:LLC-PK1 Cells; D013552:Swine; D014498:Uracil / Q000493:pharmacokinetics*
chemical_list: D014498:Uracil