Abstract
The autacoid and neurotransmitter histamine activates the H1 G protein-coupled receptor (GPCR) to stimulate predominantly phospholipase C (PLC)/inositol phosphate (IP) signaling and, to a lesser extent, adenylyl cyclase (AC)/cAMP signaling in a variety of mammalian cells and tissues, as well as H1-transfected clonal cell lines. This study reports that two novel H1 receptor ligands developed in our laboratory, (-)-trans-1-phenyl-3-dimethylamino-1,2,3,4-tetrahydronaphthalene (trans-PAT) and (±)-cis-5-phenyl-7-dimethylamino-5,6,7,8-tetrahydro-9H-benzocycloheptane (cis-PAB), activate H1 receptors to selectively stimulate AC/cAMP formation and PLC/IP formation, respectively, in Chinese hamster ovary cells transfected with guinea pig H1 receptor cDNA. trans-PAT and cis-PAB also are shown to be functionally selective antagonists of H1-linked PLC/IP and AC/cAMP signaling, respectively. Whereas cis-PAB H1 receptor activity is shown to be typically competitive, trans-PAT displays a complex interaction with the H1 receptor that is not competitive regarding antagonism of saturation binding by the standard H1 antagonist radioligand [3H]mepyramine or H1/PLC/IP functional activation by histamine. trans-PAT, however, does competitively block H1/PLC/IP functional activation by cis-PAB. Molecular determinants for trans-PAT versus cis-PAB differential binding to H1 receptors, which presumably leads to differential activation of AC/cAMP versus PLC/IP signaling, likely involves stereochemical factors as well as more subtle steric influences. Results suggest the trans-PAT and cis-PAB probes will be useful to study molecular mechanisms of ligand-directed GPCR multifunctional signaling. Moreover, because most untoward cardiovascular-, respiratory-, and gastrointestinal H1 receptor-mediated effects proceed via the PLC/IP pathway, PAT-type agonists that selectively enhance H1-mediated AC/cAMP signaling provide a mechanistic basis for exploiting H1 receptor activation for drug design purposes.
Footnotes
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This work was supported by U.S. Public Health Service Grants MH068655 and NS35216 and the Pharmacy Foundation of North Carolina.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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doi:10.1124/jpet.104.070086.
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ABBREVIATIONS: GPCR, G protein-coupled receptor; PLC, phospholipase C; IP, inositol phosphate(s); AC, adenylyl cyclase; CHO, Chinese hamster ovary; PAT, 1-phenyl-3-dimethylamino-1,2,3,4-tetrahydronaphthalene; PAB, 5-phenyl-7-(dimethylamino)-5,6,7,8-tetrahydro-9H-benzocycloheptane; ANOVA, analysis of variance; 5-HT, 5-hydroxytryptamine; TMH, transmembrane helix.
- Received April 16, 2004.
- Accepted May 28, 2004.
- The American Society for Pharmacology and Experimental Therapeutics
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