Allosteric modulation of adenosine A1 receptor coupling to G‐proteins in brain

• Published in: Journal of neurochemistry 2005-05, Vol.93 (3), p.715-723
• Main Authors: Childers, Steven R., Li, Xinhui, Xiao, Ruoyu, Eisenach, James C.
• Format: Article
• Language: English
• Subjects: [35S]GTPγS; adenosine A1 receptor; Adenosine A1 Receptor Agonists; allosteric; Allosteric Regulation - drug effects; Allosteric Regulation - physiology; Animals; autoradiography; Biological and medical sciences; Brain - drug effects; Brain - metabolism; Cell receptors; Cell structures and functions; Degenerative and inherited degenerative diseases of the nervous system. Leukodystrophies. Prion diseases; Fundamental and applied biological sciences. Psychology; GTP-Binding Proteins - agonists; GTP-Binding Proteins - metabolism; Guanosine 5'-O-(3-Thiotriphosphate) - metabolism; Guanosine 5'-O-(3-Thiotriphosphate) - pharmacology; G‐proteins; Male; Medical sciences; modulator; Molecular and cellular biology; Monoamines receptors (catecholamine, serotonine, histamine, acetylcholine); Neurology; Protein Binding - drug effects; Protein Binding - physiology; Rats; Rats, Sprague-Dawley; Receptor, Adenosine A1 - metabolism
• ISSN: 0022-3042; 1471-4159
• DOI: 10.1111/j.1471-4159.2005.03044.x

2‐Amino‐4,5,6,7‐tetrahydrobenzo(β)thiophen‐3‐yl 4‐chlorophenylmethanone (T62) is a member of a group of allosteric modulators of adenosine A1 receptors tested in animal models of neuropathic pain to increase the efficacy of adenosine. To determine its mechanisms at the level of receptor‐G‐protein activation, the present studies examined the effect of T62 on A1‐stimulated [35S]guanosine‐5′‐O‐(γ‐thio)‐triphosphate ([35S]GTPγS) binding in brain membranes, and by [35S]GTPγS autoradiography using the A1 agonist, phenylisopropyladenosine (PIA), to activate G‐proteins. In hippocampal membranes, T62 increased both basal and PIA‐stimulated [35S]GTPγS binding. The effect of T62 was non‐competitive in nature, since it increased the maximal effect of PIA, with no effect on agonist potency. GTPγS saturation analysis showed that T62 increased the number of G‐proteins activated by agonist but had no effect on the affinity of activated G‐proteins for GTPγS. [35S]GTPγS autoradiography showed that the neuroanatomical localization of T62‐stimulated [35S]GTPγS binding was identical to that of PIA‐stimulated activity. The increase in PIA‐stimulated activity by T62 varied between brain regions, with areas of lower A1 activation producing the largest percent modulation by T62. These results suggest a mechanism of allosteric modulators to increase the number of activated G‐proteins per receptor, and provide a neuroanatomical basis for understanding potential therapeutic effects of such drugs.