title: Examining the Effects of Sodium Ions on the Binding of Antagonists to Dopamine D2 and D3 Receptors.
abstract: Many G protein-coupled receptors have been shown to be sensitive to the presence of sodium ions (Na+). Using radioligand competition binding assays, we have examined and compared the effects of sodium ions on the binding affinities of a number of structurally diverse ligands at human dopamine D2 and dopamine D3 receptor subtypes, which are important therapeutic targets for the treatment of psychotic disorders. At both receptors, the binding affinities of the antagonists/inverse agonists SB-277011-A, L,741,626, GR 103691 and U 99194 were higher in the presence of sodium ions compared to those measured in the presence of the organic cation, N-methyl-D-glucamine, used to control for ionic strength. Conversely, the affinities of spiperone and (+)-butaclamol were unaffected by the presence of sodium ions. Interestingly, the binding of the antagonist/inverse agonist clozapine was affected by changes in ionic strength of the buffer used rather than the presence of specific cations. Similar sensitivities to sodium ions were seen at both receptors, suggesting parallel effects of sodium ion interactions on receptor conformation. However, no clear correlation between ligand characteristics, such as subtype selectivity, and sodium ion sensitivity were observed. Therefore, the properties which determine this sensitivity remain unclear. However these findings do highlight the importance of careful consideration of assay buffer composition for in vitro assays and when comparing data from different studies, and may indicate a further level of control for ligand binding in vivo.
authors.affiliation: School of Pharmacy, University of Reading, Reading, RG6 6AJ, United Kingdom.
authors.forename: Claire L
authors.identifier: http://orcid.org/0000-0001-6050-556X
authors.initials: CL
authors.lastname: Newton
authors.affiliation: Psychiatry CEDD, GlaxoSmithKline, Harlow, Essex, CM19 5AW, United Kingdom.
authors.forename: Martyn D
authors.initials: MD
authors.lastname: Wood
authors.affiliation: School of Pharmacy, University of Reading, Reading, RG6 6AJ, United Kingdom.
authors.forename: Philip G
authors.initials: PG
authors.lastname: Strange
mesh_terms: D000818:Animals; D001667:Binding, Competitive; D001713:Biphenyl Compounds / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D045744:Cell Line, Tumor; D018491:Dopamine Agonists / Q000378:metabolism / Q000494:pharmacology; D018492:Dopamine Antagonists / Q000378:metabolism* / Q000494:pharmacology; D065127:Dopamine D2 Receptor Antagonists / Q000378:metabolism* / Q000494:pharmacology; D006801:Humans; D007189:Indans / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D007211:Indoles / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D007477:Ions / Q000378:metabolism; D008024:Ligands; D015394:Molecular Structure; D009154:Mutation; D009570:Nitriles / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010879:Piperazines / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D010880:Piperidines / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology; D011869:Radioligand Assay; D017448:Receptors, Dopamine D2 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D050637:Receptors, Dopamine D3 / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D061987:Sf9 Cells; D012964:Sodium / Q000378:metabolism*; D018411:Spodoptera; D044005:Tetrahydroisoquinolines / Q000737:chemistry / Q000378:metabolism / Q000494:pharmacology
chemical_list: D001713:Biphenyl Compounds; D018491:Dopamine Agonists; D018492:Dopamine Antagonists; D065127:Dopamine D2 Receptor Antagonists; D007189:Indans; D007211:Indoles; D007477:Ions; D008024:Ligands; D009570:Nitriles; D010879:Piperazines; D010880:Piperidines; D017448:Receptors, Dopamine D2; D050637:Receptors, Dopamine D3; C409982:SB 277011; D044005:Tetrahydroisoquinolines; C105771:GR 103691; C086335:(5,6-dimethoxyindan-2-yl)dipropylamine; C104750:3-(4-(4-chlorophenyl-4-hydroxypiperidino)methyl)indole; D012964:Sodium