Development of a radioligand binding assay for 5-HT4 receptors in guinea-pig and rat brain.
1. The 5-HT4 receptor antagonist, GR113808, has been radiolabelled to a high specific activity with tritium. 2. Characterization of specific [3H]-GR113808 binding in homogenates of guinea-pig striatum and hippocampus revealed a single site of high affinity (Kd values 0.20 and 0.13 nM respectively). 3. [3H]-GR113808 binding was reversible and displayed rapid kinetics such that association and dissociation were complete within 3 min. 4. Specific [3H]-GR113808 binding was potently and stereoselectively inhibited by agonists and antagonists acting at the 5-HT4 receptor but not by compounds selective for other 5-HT receptors or other neurotransmitter receptors. 5. Autoradiographic analysis revealed a discrete localization in both guinea-pig and rat brain with high concentrations of binding in brain areas such as the striatum, substantia nigra and olfactory tubercle. 6. [3H]-GR113808 binding to homogenates of guinea-pig striatum meets the criteria for labelling of the 5-HT4 receptor and, as such, represents the first characterization of this receptor in a radioligand binding assay.
Grossman
C J
CJ
Pharmacology Division, Glaxo Group Research Ltd., Ware, Herts.
Kilpatrick
G J
GJ
Bunce
K T
KT
D000818:Animals; D001345:Autoradiography; D001667:Binding, Competitive / Q000187:drug effects; D001923:Brain Chemistry / Q000187:drug effects*; D003342:Corpus Striatum / Q000378:metabolism; D006168:Guinea Pigs; D006624:Hippocampus / Q000378:metabolism; D066298:In Vitro Techniques; D007211:Indoles / Q000493:pharmacokinetics*; D009419:Nerve Tissue Proteins / Q000378:metabolism; D011869:Radioligand Assay; D051381:Rats; D011985:Receptors, Serotonin / Q000187:drug effects*; D012702:Serotonin Antagonists / Q000494:pharmacology; D017366:Serotonin Receptor Agonists / Q000494:pharmacology; D013237:Stereoisomerism; D013449:Sulfonamides / Q000493:pharmacokinetics*
D007211:Indoles; D009419:Nerve Tissue Proteins; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; D017366:Serotonin Receptor Agonists; D013449:Sulfonamides; C082871:GR 113808