G Protein-Dependent Pharmacology of Histamine H3 Receptor Ligands: Evidence for Heterogeneous Active State Receptor Conformations
| Autor: | S A Buckner, Lynne Ireland-Denny, Thomas R. Miller, Ivan Milicic, Kathleen M. Krueger, Timothy A. Esbenshade, John L. Baranowski, Arthur A. Hancock, David G. Witte |
|---|---|
| Rok vydání: | 2005 |
| Předmět: |
Male
Agonist Clobenpropit Protein Conformation medicine.drug_class G protein Guinea Pigs Histamine Antagonists Biology Pharmacology Ligands Transfection Imetit Histamine Release Receptors G-Protein-Coupled Histamine Agonists Rats Sprague-Dawley Radioligand Assay chemistry.chemical_compound GTP-Binding Proteins Ileum Ciproxifan Cyclic AMP medicine Animals Receptors Histamine H3 Receptor Neurotransmitter Agents Membranes Imidazoles Electric Stimulation Rats Biochemistry chemistry Guanosine 5'-O-(3-Thiotriphosphate) Proxyfan Molecular Medicine Histamine H3 receptor Signal Transduction medicine.drug |
| Zdroj: | Journal of Pharmacology and Experimental Therapeutics. 314:271-281 |
| ISSN: | 1521-0103 0022-3565 |
| Popis: | Previously reported pharmacological studies using the imidazole-containing histamine H3 receptor ligands GT-2331 (Cipralisant) and proxyfan resulted in a range of classifications (antagonist, agonist, and protean) for these compounds. We examined the role that the signaling system, with particular emphasis on the type of G protein, had on the pharmacology observed for H3 ligands. Ligands were assessed using assays measuring neurotransmitter release, cAMP, and guanosine 5'-O-(3-[35S]thio)triphosphate ([35S]GTPgammaS) binding. Whereas clobenpropit and ciproxifan were consistently antagonists, GT-2331, proxyfan, and imetit exhibited differential activity. Although GT-2331 and proxyfan exhibited little agonist activity in neurotransmitter release assays, both demonstrated full agonism relative to (R)-alpha-methylhistamine in cAMP assays. In [35S]GTPgammaS binding assays, GT-2331 and proxyfan demonstrated partial agonism. Imetit showed full agonism in most assays, but it was slightly less efficacious in a neurotransmitter release assay and in [35S]GTPgammaS binding at the human H3 receptor. To further examine these ligands, we coexpressed G alpha16 or chimeric G alpha q/i5 in human embryonic kidney cells expressing the human H3 receptor and assayed intracellular calcium and cAMP levels. GT-2331, proxyfan, and imetit demonstrated full agonism in all assays of cAMP activity. However, in cells expressing G alpha16, they exhibited minimal agonism in calcium mobilization assays, whereas imetit showed partial agonism. When G alpha q/i5 was used, the activity of both GT-2331 and proxyfan increased, whereas imetit became a full agonist. These results demonstrate that GT-2331 and proxyfan's differential pharmacology at the H3 receptor depends on the type of G protein used and provide indirect evidence for differential ligand-bound active states that mediate signaling by the H3 receptor. |
| Databáze: | OpenAIRE |
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