title: Constitutive activity and ligand selectivity of human, guinea pig, rat, and canine histamine H2 receptors.
abstract: Previous studies revealed pharmacological differences between human and guinea pig histamine H(2) receptors (H(2)Rs) with respect to the interaction with guanidine-type agonists. Because H(2)R species variants are structurally very similar, comparative studies are suited to relate different properties of H(2)R species isoforms to few molecular determinants. Therefore, we systematically compared H(2)Rs of human (h), guinea pig (gp), rat (r), and canine (c). Fusion proteins of hH(2)R, gpH(2)R, rH(2)R, and cH(2)R, respectively, and the short splice variant of G(salpha), G(salphaS), were expressed in Sf9 insect cells. In the membrane steady-state GTPase activity assay, cH(2)R-G(salphaS) but neither gpH(2)R-G(salphaS) nor rH(2)R-G(salphaS) showed the hallmarks of increased constitutive activity compared with hH(2)R-G(salphaS), i.e., increased efficacies of partial agonists, increased potencies of agonists with the extent of potency increase being correlated with the corresponding efficacies at hH(2)R-G(salphaS), increased inverse agonist efficacies, and decreased potencies of antagonists. Furthermore, in membranes expressing nonfused H(2)Rs without or together with mammalian G(salphaS) or H(2)R-G(salpha) fusion proteins, the highest basal and GTP-dependent increases in adenylyl cyclase activity were observed for cH(2)R. An example of ligand selectivity is given by metiamide, acting as an inverse agonist at hH(2)R-G(salphaS), gpH(2)R-G(salphaS), and rH(2)R-G(salphaS) in the GTPase assay in contrast to being a weak partial agonist with decreased potency at cH(2)R-G(salphaS). In conclusion, the cH(2)R exhibits increased constitutive activity compared with hH(2)R, gpH(2)R, and rH(2)R, and there is evidence for ligand-specific conformations in H(2)R species isoforms.
authors.affiliation: Department of Pharmaceutical/Medicinal Chemistry II, Institute of Pharmacy, University of Regensburg, Regensburg, Germany.
authors.forename: Hendrik
authors.initials: H
authors.lastname: Preuss
authors.forename: Prasanta
authors.initials: P
authors.lastname: Ghorai
authors.forename: Anja
authors.initials: A
authors.lastname: Kraus
authors.forename: Stefan
authors.initials: S
authors.lastname: Dove
authors.forename: Armin
authors.initials: A
authors.lastname: Buschauer
authors.forename: Roland
authors.initials: R
authors.lastname: Seifert
mesh_terms: D000262:Adenylyl Cyclases / Q000378:metabolism; D000818:Animals; D016367:Baculoviridae / Q000235:genetics; D002460:Cell Line; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism; D004285:Dogs; D020558:GTP Phosphohydrolases / Q000378:metabolism; D019205:GTP-Binding Protein alpha Subunits, Gs / Q000235:genetics / Q000378:metabolism; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D017442:Histamine Agonists / Q000494:pharmacology*; D006635:Histamine H2 Antagonists / Q000494:pharmacology*; D006801:Humans; D008024:Ligands; D008785:Metiamide / Q000494:pharmacology; D051381:Rats; D011970:Receptors, Histamine H2 / Q000235:genetics / Q000378:metabolism*; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D011994:Recombinant Proteins / Q000378:metabolism; D013045:Species Specificity; D018411:Spodoptera; D014162:Transfection
chemical_list: D017442:Histamine Agonists; D006635:Histamine H2 Antagonists; D008024:Ligands; D011970:Receptors, Histamine H2; D011993:Recombinant Fusion Proteins; D011994:Recombinant Proteins; D008785:Metiamide; D006632:Histamine; D020558:GTP Phosphohydrolases; D019205:GTP-Binding Protein alpha Subunits, Gs; D000262:Adenylyl Cyclases