Platelet plasma membrane: characterization of the serotonin transporter]

After treatment of human platelets by a sulfhydryl-dependent bacterial protein cytolysin, a glycoprotein was reproducibly purified by a one-step affinity chromatography using 6-fluorotryptamine as ligand and elution by serotonin (5-HT), cyanoimipramine, citalopram, or a Na(+)-free buffer. The purified fraction migrated on sodium dodecyl sulfate-polyacrylamide gel electrophoresis as a single band with an apparent molecular mass of 68 kDa. The purified glycoprotein bound the 5-HT uptake blockers 3H-paroxetine, 3H-cyanoimipramine, and 3H-citalopram with Kds similar to the ones observed for intact human platelets. No binding was detected with 3H-hydroxytetrabenazine, 3H-ouabain, 3H-gamma aminobutyric acid or 3H-BTCP, the respective markers of the granular monoamine transporter, the plasma membrane Na+, K(+)-ATPase, the gamma aminobutyric acid and dopamine carriers. The purified 68-kDa glycoprotein is therefore likely to correspond at least to the paroxetine and imipramine binding domains of the 5-HT transporter located at the human platelet plasma membrane. Finally a 68-kDa protein was purified in the same conditions from the human megakaryocytic cell line Dami and to a lesser extent from the human megakaryoblastic cell line MEG-01 but not from the human erythroleukaemic cell line HEL.