Abstract
Species isoforms of histamine H2-, H3-, and H4-receptors differ in their pharmacological properties. The study aim was to dissect differences between the human H1R (hH1R) and guinea pig H1R (ghH1R). We coexpressed hH1R and gpH1R with regulators of G-protein signaling in Sf9 insect cells and analyzed the GTPase activity of Gq-proteins. Small H1R agonists showed similar effects at hH1R and gpH1R, whereas bulkier 2-phenylhistamines and histaprodifens were up to ∼10-fold more potent at gpH1R than at hH1R. Most 2-phenylhistamines and histaprodifens were more efficacious at gpH1R than at hH1R. Several first-generation H1R antagonists were ∼2-fold, and arpromidine-type H1R antagonists up to ∼10-fold more potent at gpH1R than at hH1R. [3H]Mepyramine competition binding studies confirmed the potency differences of the GTPase studies. Phe-153→Leu-153 or Ile-433→Val-433 exchange in hH1R (hH1R→gpH1R) resulted in poor receptor expression, low [3H]mepyramine affinity, and functional inactivity. The Phe-153→Leu-153/Ile-433→Val-433 double mutant expressed excellently but only partially changed the pharmacological properties of hH1R. Small H1R agonists and 2-phenylhistamines interacted differentially with human and guinea pig H2R in terms of potency and efficacy, respectively. Our data show the following: 1) there are differences in agonist- and antagonist-pharmacology of hH1R and gpH1R encompassing diverse classes of bulky ligands. These differences may be explained by higher conformational flexibility of gpH1R relative to hH1R; 2) Phe-153 and Ile-433 are critical for proper folding and expression of hH1R; and 3) H2R species isoforms distinguish between H1R agonists.
Footnotes
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This work was supported by the National Institutes of Health COBRE Award 1 P20 RR15563 and matching support from the State of Kansas and the University of Kansas (R.S.), a grant from the Army Research Office (DAAD 19-00-1-006) (R.S.), grants of the Deutsche Forschungsgemeinschaft (W.S. and A.B.), Fonds der Chemischen Industrie (T.B., W.S., A.B., and S.E.), the Bundesministerium für Bildung und Forschung (T.B.), and the Deutscher Akademischer Austauschdienst within the International Quality Network “Medicinal Chemistry” (S.E. and A.B.).
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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.103.049619.
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ABBREVIATIONS: HxR, histamine H1-, H2-, H3-, or H4-receptor; h, human; gp, guinea pig; GPCR, G-protein-coupled receptor; TM, transmembrane domain; RGS protein, regulator of G-protein signaling; GAIP, Gα-interacting protein; PAGE, polyacrylamide gel electrophoresis; gpH2R-GsαS, fusion protein of the guinea pig histamine H2-receptor and the short splice variant of Gsα;hH1R, human histamine H1-receptor; hH2R, human histamine H2-receptor; hH2R-GsαS, fusion protein of the human histamine H2-receptor and the short splice variant of Gsα; hH1R-F153L, human histamine H1-receptor bearing a Phe→Leu exchange at position 153; hH1R-I433V, human histamine H1-receptor bearing an Ile→Val exchange at position 433; hH1R-F153L/I433V, human histamine H1-receptor bearing a Phe→Leu exchange at position 153 and an Ile→Val exchange at position 433.
- Received January 28, 2003.
- Accepted February 21, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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