title: The hypocretins are weak agonists at recombinant human orexin-1 and orexin-2 receptors.
abstract: The pharmacology of the orexin-like peptides, hypocretin-1 and hypocretin-2, was studied in Chinese hamster ovary (CHO) cells stably expressing orexin-1 (OX(1)) or orexin-2 (OX(2)) receptors by measuring intracellular calcium ([Ca(2+)](i)) using Fluo-3AM. Orexin-A and orexin-B increased [Ca(2+)](i) in CHO-OX(1) (pEC(50)=7. 99+/-0.05 and 7.00+/-0.10 respectively, n=8) and CHO-OX(2) (pEC(50)=8.30+/-0.05 and 8.21+/-0.07 respectively, n=5). However, hypocretin-1 and hypocretin-2 were markedly less potent, with pEC(50) values of 5.31+/-0.04 and 5.41+/-0.04 respectively in CHO-OX(2) cells (n=5). In CHO-OX(1) cells 10 microM hypocretin-1 only elicited a 37.5+/-3.4% response whilst 10 microM hypocretin-2 elicited a 18.0+/-2.1% response (n=8). Desensitisation of OX(1) or OX(2) with orexin-A (100 nM) abolished the response to orexin-A (10 nM) and the hypocretins (10 microM), but not to UTP (3 microM). In conclusion, the hypocretins are only weak agonists at the orexin receptors.
authors.affiliation: Neuroscience Research, SmithKline Beecham Pharmaceuticals, New Frontiers Science Park, Third Avenue, Harlow, Essex CM19 5AW, UK. Darren_2_Smart@sbphrd.com
authors.forename: D
authors.initials: D
authors.lastname: Smart
authors.forename: J C
authors.initials: JC
authors.lastname: Jerman
authors.forename: S J
authors.initials: SJ
authors.lastname: Brough
authors.forename: W A
authors.initials: WA
authors.lastname: Neville
authors.forename: F
authors.initials: F
authors.lastname: Jewitt
authors.forename: R A
authors.initials: RA
authors.lastname: Porter
mesh_terms: D000814:Aniline Compounds; D000818:Animals; D016466:CHO Cells; D002118:Calcium / Q000378:metabolism; D002352:Carrier Proteins / Q000494:pharmacology; D006224:Cricetinae; D004305:Dose-Response Relationship, Drug; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides / Q000494:pharmacology; D018377:Neurotransmitter Agents / Q000494:pharmacology*; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide / Q000819:agonists* / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000819:agonists / Q000235:genetics / Q000378:metabolism; D014966:Xanthenes
chemical_list: D000814:Aniline Compounds; D002352:Carrier Proteins; C000596229:HCRT protein, human; D047908:Intracellular Signaling Peptides and Proteins; D009479:Neuropeptides; D018377:Neurotransmitter Agents; D064446:Orexin Receptors; D000068797:Orexins; D043562:Receptors, G-Protein-Coupled; D018013:Receptors, Neuropeptide; D011993:Recombinant Fusion Proteins; D014966:Xanthenes; C059715:Fluo-3; D002118:Calcium