title: Antagonist-radioligand binding to D2L-receptors in intact cells.
abstract: D(2)-dopamine receptors mediate most of the physiological actions of dopamine and are important recognition sites for antipsychotic drugs. Earlier binding studies were predominantly done with broken cell preparations with the tritiated D(2)-receptor antagonists [(3)H]-raclopride, a hydrophilic benzamide, and [(3)H]-spiperone, a highly hydrophobic butyrophenone. Here we compared [(3)H]-raclopride and [(3)H]-spiperone binding properties in intact Chinese Hamster Ovary cells stably expressing recombinant human D(2L)-receptors. Specific binding of both radioligands occurred to a comparable number of sites. In contrast to the rapid dissociation of [(3)H]-raclopride in both medium only and in the presence of an excess of unlabelled ligand [(3)H]-spiperone dissociation was only observed in the latter condition, and it was still slower than in broken cell preparations. However, this could not explain the pronounced difference in the potency of some unlabelled ligands to compete with both radioligands. To integrate these new findings, a model is proposed in which raclopride approaches the receptor from the aqueous phase, while spiperone approaches the receptor by lateral diffusion within the membrane.
authors.affiliation: Free University of Brussels (VUB), Department of Molecular and Biochemical Pharmacology, Institute for Molecular Biology and Biotechnology, Pleinlaan 2, B-1050 Brussels, Belgium. apackeu@vub.ac.be
authors.forename: Ann
authors.initials: A
authors.lastname: Packeu
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: De Backer
authors.forename: Isabelle
authors.initials: I
authors.lastname: Van Liefde
authors.forename: Patrick M L
authors.initials: PM
authors.lastname: Vanderheyden
authors.forename: Georges
authors.initials: G
authors.lastname: Vauquelin
mesh_terms: D000818:Animals; D016466:CHO Cells; D003198:Computer Simulation; D006224:Cricetinae; D003412:Cricetulus; D003903:Deuterium; D018492:Dopamine Antagonists / Q000737:chemistry / Q000378:metabolism*; D065127:Dopamine D2 Receptor Antagonists; D006801:Humans; D008024:Ligands; D020891:Raclopride / Q000737:chemistry / Q000378:metabolism*; D011869:Radioligand Assay; D017448:Receptors, Dopamine D2 / Q000235:genetics / Q000378:metabolism; D013134:Spiperone / Q000737:chemistry / Q000378:metabolism*; D013997:Time Factors
chemical_list: D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D008024:Ligands; D017448:Receptors, Dopamine D2; C113776:dopamine D2L receptor; D020891:Raclopride; D013134:Spiperone; D003903:Deuterium