title: The organic cation transporter OCT2 mediates the uptake of beta-adrenoceptor antagonists across the apical membrane of renal LLC-PK(1) cell monolayers.
abstract: Previous studies have shown that beta-adrenoceptor antagonists may be substrates of organic cation transporters in kidney and lung. In this study we examined the transport of the beta-adrenoreceptor antagonists propranolol and metoprolol, in renal LLC-PK(1) cell monolayers. Experiments with BCECF (2', 7'-bis(2carboxyethyl)-5(6)-carboxyfluorescein) loaded LLC-PK(1) cell monolayers demonstrated that metoprolol and propranolol flux across the basolateral membrane was consistent with non-ionic diffusion. Flux across the apical membrane consisted of both non-ionic diffusion and the uptake of the cationic form of the beta-adrenoceptor antagonists. Uptake of the cationic form of metoprolol across the apical membrane was Na(+)-independent, electrogenic and sensitive to external pH. Furthermore, uptake was sensitive to inhibition by Decynium-22 and the organic cations TEA (tetraethylammonium) and MPP(+) (1-methyl 4-phenylpyridinium). These results, allied with the apical location of the uptake mechanism suggest that beta-adrenoceptor antagonists may be substrates for the organic cation transporter, OCT2. To confirm beta-adrenoceptor antagonists as substrates for OCT2, we demonstrate, in cells transiently transfected with an epitope tagged version of hOCT2 (hOCT2-V5):(1) Decynium-22 sensitive [(14)C]-propranolol uptake, (2) cis-inhibition of OCT2 by a range of beta-adrenoceptor antagonists and (3) metoprolol induced intracellular acidification.
authors.affiliation: Department of Physiological Sciences, The Medical School, University of Newcastle-upon-Tyne, Newcastle-uponTyne NE2 4HH.
authors.forename: A J
authors.initials: AJ
authors.lastname: Dudley
authors.forename: K
authors.initials: K
authors.lastname: Bleasby
authors.forename: C D
authors.initials: CD
authors.lastname: Brown
mesh_terms: D000319:Adrenergic beta-Antagonists / Q000493:pharmacokinetics*; D001692:Biological Transport; D002352:Carrier Proteins / Q000502:physiology*; D002478:Cells, Cultured; D002927:Cimetidine / Q000493:pharmacokinetics; D006863:Hydrogen-Ion Concentration; D007668:Kidney / Q000166:cytology / Q000378:metabolism*; D008790:Metoprolol / Q000493:pharmacokinetics / Q000494:pharmacology; D027701:Organic Cation Transport Proteins; D000075102:Organic Cation Transporter 2; D011433:Propranolol / Q000493:pharmacokinetics; D011804:Quinolines / Q000494:pharmacology
chemical_list: D000319:Adrenergic beta-Antagonists; D002352:Carrier Proteins; D027701:Organic Cation Transport Proteins; D000075102:Organic Cation Transporter 2; D011804:Quinolines; C100590:Slc22a2 protein, rat; C100254:pseudoisocyanine; D002927:Cimetidine; D011433:Propranolol; D008790:Metoprolol