title: Protean agonism at the dopamine D2 receptor: (S)-3-(3-hydroxyphenyl)-N-propylpiperidine is an agonist for activation of Go1 but an antagonist/inverse agonist for Gi1,Gi2, and Gi3.
abstract: A range of ligands displayed agonism at the long isoform of the human dopamine D(2) receptor, whether using receptor-G protein fusions or membranes of cells in which pertussis toxin-resistant mutants of individual Galpha(i)-family G proteins could be expressed in an inducible fashion. Varying degrees of efficacy were observed for individual ligands as monitored by their capacity to load [(35)S]GTPgammaS onto each of Galpha(i1),Galpha(i2),Galpha(i3), and Galpha(o1). By contrast, (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine was a partial agonist when Galpha(o1) was the target G protein but an antagonist/inverse agonist at Galpha(i1),Galpha(i2), and Galpha(i3). In ligand binding assays, dopamine identified both high- and low-affinity states at each of the dopamine D(2) receptor-G protein fusion proteins, and the high-affinity state was eliminated by guanine nucleotide. (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine bound to an apparent single state of the constructs in which the D(2) receptor was fused to Galpha(i1),Galpha(i2), or Galpha(i3). However, it bound to distinct high- and low-affinity states of the D(2) receptor-Galpha(o1) fusion, with the high-affinity state being eliminated by guanine nucleotide. Likewise, although dopamine identified guanine nucleotide-sensitive high-affinity states of the D(2) receptor when expression of pertussis toxin-resistant forms of each of Galpha(i1), Galpha(i2), Galpha(i3), and Galpha(o1) was induced, (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine identified a high-affinity site only in the presence of Galpha(o1). p-Tyramine displayed a protean ligand profile similar to that of (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine but with lower potency. These results demonstrate (S)-(-)-3-(3-hydroxyphenyl)-N-propylpiperidine to be a protean agonist at the D(2) receptor and may explain in vivo actions of this ligand.
authors.affiliation: Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow, Scotland, United Kingdom.
authors.forename: J Robert
authors.initials: JR
authors.lastname: Lane
authors.forename: Ben
authors.initials: B
authors.lastname: Powney
authors.forename: Alan
authors.initials: A
authors.lastname: Wise
authors.forename: Steven
authors.initials: S
authors.lastname: Rees
authors.forename: Graeme
authors.initials: G
authors.lastname: Milligan
mesh_terms: D000818:Animals; D001665:Binding Sites / Q000187:drug effects; D002460:Cell Line; D004298:Dopamine / Q000378:metabolism; D051960:GTP-Binding Protein alpha Subunit, Gi2 / Q000037:antagonists & inhibitors; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000819:agonists* / Q000037:antagonists & inhibitors* / Q000378:metabolism; D016244:Guanosine 5'-O-(3-Thiotriphosphate) / Q000378:metabolism; D006801:Humans; D008024:Ligands; D050505:Mutant Proteins / Q000378:metabolism; D037342:Pertussis Toxin; D010880:Piperidines / Q000494:pharmacology*; D051381:Rats; D017448:Receptors, Dopamine D2 / Q000819:agonists* / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D013552:Swine
chemical_list: C522851:Gnai1 protein, rat; D008024:Ligands; D050505:Mutant Proteins; D010880:Piperidines; D017448:Receptors, Dopamine D2; D011993:Recombinant Fusion Proteins; C050328:3-(3,4-dihydroxyphenyl)-N-n-propylpiperidine; D016244:Guanosine 5'-O-(3-Thiotriphosphate); D037342:Pertussis Toxin; D051960:GTP-Binding Protein alpha Subunit, Gi2; D019206:GTP-Binding Protein alpha Subunits, Gi-Go; C498820:Gnai3 protein, rat; D004298:Dopamine