title: 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.
abstract: OBJECTIVE
  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.
  
  
  METHODS
  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.
  
  
  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
  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.
authors.affiliation: Albany Medical College, Center for Neuropharmacology & Neuroscience, 47 New Scotland Avenue, MC 136, Albany, NY 12208, USA.
authors.forename: M T
authors.initials: MT
authors.lastname: Klein
authors.forename: M
authors.initials: M
authors.lastname: Teitler
mesh_terms: D000262:Adenylyl Cyclases / Q000187:drug effects* / Q000378:metabolism; D003024:Clozapine / Q000494:pharmacology; D005576:Colforsin / Q000494:pharmacology; D000242:Cyclic AMP / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D043562:Receptors, G-Protein-Coupled / Q000378:metabolism*; D011985:Receptors, Serotonin / Q000187:drug effects* / Q000378:metabolism; D012702:Serotonin Antagonists / Q000494:pharmacology*
chemical_list: D043562:Receptors, G-Protein-Coupled; D011985:Receptors, Serotonin; D012702:Serotonin Antagonists; C104425:serotonin 7 receptor; D005576:Colforsin; D000242:Cyclic AMP; D000262:Adenylyl Cyclases; D003024:Clozapine