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Antagonist interaction with the human 5‐HT 7 receptor mediates the rapid and potent inhibition of non‐G‐protein‐stimulated adenylate cyclase activity: a novel GPCR effect
Author(s) -
Klein MT,
Teitler M
Publication year - 2011
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.2010.01194.x
Subject(s) - forskolin , receptor , medicine , g protein coupled receptor , endocrinology , biology , competitive antagonist , antagonist , receptor antagonist , g protein , chemistry , pharmacology , biochemistry
BACKGROUND AND PURPOSE The human 5‐hydroxytryptamine 7 (h5‐HT 7 ) receptor is G s ‐coupled and stimulates the production of the intracellular signalling molecule cAMP. Previously, we reported a novel property of the h5‐HT 7 receptor: pseudo‐irreversible antagonists irreversibly inhibit forskolin‐stimulated (non‐receptor‐mediated) cAMP production. Herein, we sought to determine if competitive antagonists also affect forskolin‐stimulated activity and if this effect is common among other G s ‐coupled receptors. EXPERIMENTAL APPROACH Recombinant cell lines expressing h5‐HT 7 receptors or other receptors of interest were briefly exposed to antagonists; cAMP production was then stimulated by forskolin and quantified by an immunocompetitive assay. KEY RESULTS In human embryonic kidney 293 cells stably expressing h5‐HT 7 receptors, all competitive antagonists inhibited nearly 100% of forskolin‐stimulated cAMP production. This effect was insensitive to pertussis toxin, that is, not G i/o ‐mediated. Potency to inhibit forskolin‐stimulated activity strongly correlated with h5‐HT 7 binding affinity ( r 2 = 0.91), indicating that the antagonists acted through h5‐HT 7 receptors to inhibit forskolin. Potency and maximal effects of clozapine, a prototypical competitive h5‐HT 7 antagonist, were unaffected by varying forskolin concentration. Antagonist interaction with h5‐HT 6 , human β 1 , β 2 , and β 3 adrenoceptors did not inhibit forskolin's activity. CONCLUSIONS AND IMPLICATIONS The inhibition of adenylate cyclase, as measured by forskolin's activity, is an underlying property of antagonist interaction with h5‐HT 7 receptors; however, this is not a common property of other G s ‐coupled receptors. This phenomenon may be involved in the roles played by h5‐HT 7 receptors in human physiology. Development of h5‐HT 7 antagonists that do not elicit this effect would aid in the elucidation of its mechanisms and shed light on its possible physiological relevance.