IDENTIFICATION OF A DOPAMINE-BINDING PROTEIN ON THE MEMBRANE OF THE HUMAN PLATELET

The binding of [H-3]dopamine to platelet membranes has been examined in an attempt to identify the putative dopamine-uptake mechanism of the platelet. [H-3]Dopamine has been shown to bind to a 42000 Da glycoprotein in platelet membrane with high affinity (K(d) = 22.6 nM) and binding of [H-3]dopamine was competed for by dopamine, molecules with catechol moieties, 5-hydroxytryptamine, GSH and ascorbic acid. Differences in pharmacological profile and molecular mass suggest that [H-3]dopamine does not bind to a known receptor, a neuronal-type dopamine transporter or the platelet 5-hydroxytryptamine-uptake site. It is proposed that this novel binding site for dopamine, which has been purified 1000-fold from particulate platelet membrane, is likely to be a component of the dopamine-uptake mechanism of the human platelet.