Proton-coupled organic cation antiporter-mediated uptake of apomorphine enantiomers in human brain capillary endothelial cell line hCMEC/D3

Biol Pharm Bull. 2014;37(2):286-91. doi: 10.1248/bpb.b13-00773. Epub 2013 Nov 20.


R(-)-Apomorphine is a dopamine agonist used for rescue management of motor function impairment associated with levodopa therapy in Parkinson's disease patients. The aim of this study was to examine the role of proton-coupled organic cation antiporter in uptake of R(-)-apomorphine and its S-enantiomer in human brain, using human endothelial cell line hCMEC/D3 as a model. Uptake of R(-)- or S(+)-apomorphine into hCMEC/D3 cells was measured under various conditions to evaluate its time-, concentration-, energy- and ion-dependency. Inhibition by selected organic cations was also examined. Uptakes of both R(-)- and S(+)-apomorphine increased with time. The initial uptake velocities of R(-)- and S(+)-apomorphine were concentration-dependent, with similar Km and Vmax values. The cell-to-medium (C/M) ratio of R(-)-apomorphine was significantly reduced by pretreatment with sodium azide, but was not affected by replacement of extracellular sodium ion with N-methylglucamine or potassium. Intracellular alkalization markedly reduced the uptake, while intracellular acidification increased it, suggesting that the uptake is driven by an oppositely directed proton gradient. The C/M ratio was significantly decreased by amantadine, verapamil, pyrilamine and diphenhydramine (substrates or inhibitors of proton-coupled organic cation antiporter), while tetraethylammonium (substrate of organic cation transporters (OCTs)) and carnitine (substrate of carnitine/organic cation transporter 2; (OCTN2)) had no effect. R(-)-Apomorphine uptake was competitively inhibited by diphenhydramine. Our results indicate that R(-)-apomorphine transport in human blood-brain barrier (BBB) model cells is similar to S(+)-apomorphine uptake. The transport was dependent on an oppositely directed proton gradient, but was sodium- or membrane potential-independent. The transport characteristics were consistent with involvement of the previously reported proton-coupled organic cation antiporter.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antiporters / metabolism*
  • Apomorphine / pharmacokinetics*
  • Biological Transport
  • Blood-Brain Barrier / metabolism*
  • Cations / metabolism*
  • Cell Line
  • Dopamine Agonists / pharmacokinetics*
  • Endothelial Cells / metabolism
  • Humans
  • Hydrogen-Ion Concentration
  • Membrane Potentials
  • Organic Cation Transport Proteins / metabolism
  • Protons*
  • Sodium / metabolism
  • Stereoisomerism


  • Antiporters
  • Cations
  • Dopamine Agonists
  • Organic Cation Transport Proteins
  • Protons
  • Sodium
  • Apomorphine