title: Clonidine accumulation in human neuronal cells.
abstract: After transport across several epithelial barriers including the blood-brain barrier, clonidine interacts with alpha(2)-adrenergic receptors and imidazoline binding sites in the brain. We hypothesized that neuronal cells take up clonidine thereby removing the drug from the extracellular fluid compartment. Uptake of [(3)H]clonidine into SH-SY5Y neuroblastoma cells was linear for up to 1 min, unaffected by inside directed Na(+) or Cl(-) gradients but strongly inhibited by an outside pH of 6.0. The cells accumulated [(3)H]clonidine 50-70-fold uphill against a concentration gradient. Unlabeled clonidine, guanabenz, imipramine, diphenhydramine, maprotiline, quinine and the endogenous monoamine phenylethylamine (2 mM) strongly inhibited the [(3)H]clonidine uptake by 60-95%. Tetraethylammonium, choline and N-methyl-4-phenylpyridinium had no effect. The accumulation at pH 7.5 was saturable with an apparent Michaelis-Menten constant (K(t)) of 0.7 mM. We conclude that SH-SY5Y cells not only bind clonidine to extracellular receptors but also take up the drug rapidly by a specific and concentrative mechanism.
authors.affiliation: Membrane Transport Group, Biozentrum, Martin-Luther-University Halle-Wittenberg, Weinbergweg 22, D-06120 Halle, Germany.
authors.forename: Wiebke
authors.initials: W
authors.lastname: Fischer
authors.forename: Reinhard H H
authors.initials: RH
authors.lastname: Neubert
authors.forename: Matthias
authors.initials: M
authors.lastname: Brandsch
mesh_terms: D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D003000:Clonidine / Q000378:metabolism* / Q000493:pharmacokinetics; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007700:Kinetics; D009474:Neurons / Q000166:cytology / Q000187:drug effects / Q000378:metabolism*; D013997:Time Factors; D014316:Tritium / Q000378:metabolism / Q000493:pharmacokinetics
chemical_list: D014316:Tritium; D003000:Clonidine