A novel phenylaminotetralin radioligand reveals a subpopulation of histamine H(1) receptors.
Previously, (-)-trans-1-phenyl-3-N,N-dimethylamino-1,2,3,4-tetrahydronaphthalene ([-]-trans-H(2)-PAT) was shown to activate stereospecifically histamine H(1) receptors coupled to modulation of tyrosine hydroxylase activity in guinea pig and rat forebrain in vitro and in vivo. Furthermore, the novel radioligand [(3)H](-)-trans-H(2)-PAT was shown to label selectively H(1) receptors in guinea pig and rat brain with high affinity (K(D), ~0.1 and 0.5 nM, respectively) and a B(max) about 50 and 15%, respectively, of that observed for the H(1) antagonist radioligand [(3)H]mepyramine. In the current study, [(3)H](-)-trans-H(2)-PAT-labeled cloned guinea pig and human H(1) receptors in Chinese hamster ovary (CHO) cell membranes with high affinity (K(D), ~0.08 and 0.23 nM, respectively) and a B(max) about 15% of that observed for [(3)H]mepyramine. The binding of H(2)-PAT to H(1) receptors in both CHO-H(1) cell lines was stereoselective with the (-)-trans-isomer having affinity (K(i), ~1.5 nM) about 4-, 20-, and 50-times higher than the (-)-cis-, (+)-trans-, and (+)-cis-isomers, respectively; the affinity of (-)-trans-H(2)-PAT was unaffected by excess GTP. In functional assays, (-)-trans-H(2)-PAT was a full antagonist of histamine H(1)-mediated stimulation of phospholipase C (PLC) and [(3)H]inositol phosphates (IP) formation in CHO-H(1) cells, a full inverse agonist of constitutively active H(1) receptors in COS-7-H(1) cells, and a full competitive antagonist (pA(2) = 9.2) of histamine H(1)-mediated contraction of guinea pig ileum. It is concluded that (-)-trans-H(2)-PAT is an antagonist at H(1) receptors coupled to PLC/IP formation and smooth muscle contraction. Meanwhile, the observation that [(3)H](-)-trans-H(2)-PAT labels only a subpopulation of H(1) receptors and that (-)-trans-H(2)-PAT activates H(1) receptors coupled to modulation of tyrosine hydroxylase suggests that there may be post-translational H(1) receptor heterogeneity.
Booth
Raymond G
RG
Division of Medicinal Chemistry and Natural Products, School of Pharmacy, University of North Carolina at Chapel Hill, Chapel Hill, 27599-7360, USA. rbooth@email.unc.edu
Moniri
Nader H
NH
Bakker
Remko A
RA
Choksi
Neepa Y
NY
Nix
William B
WB
Timmerman
Henk
H
Leurs
Rob
R
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D016466:CHO Cells; D019556:COS Cells; D002462:Cell Membrane / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D002522:Chlorocebus aethiops; D006224:Cricetinae; D018076:DNA, Complementary / Q000096:biosynthesis / Q000235:genetics; D006168:Guinea Pigs; D006632:Histamine / Q000494:pharmacology; D017442:Histamine Agonists / Q000494:pharmacology; D006801:Humans; D007082:Ileum / Q000187:drug effects / Q000378:metabolism; D007295:Inositol Phosphates / Q000378:metabolism; D008024:Ligands; D016328:NF-kappa B / Q000187:drug effects; D011738:Pyrilamine; D019275:Radiopharmaceuticals / Q000494:pharmacology; D011969:Receptors, Histamine H1 / Q000187:drug effects* / Q000235:genetics; D013764:Tetrahydronaphthalenes / Q000494:pharmacology; D013816:Thermodynamics; D014162:Transfection; D010738:Type C Phospholipases / Q000378:metabolism
D018076:DNA, Complementary; D017442:Histamine Agonists; D007295:Inositol Phosphates; D008024:Ligands; D016328:NF-kappa B; D019275:Radiopharmaceuticals; D011969:Receptors, Histamine H1; D013764:Tetrahydronaphthalenes; C084981:1-phenyl-3-dimethylamino-1,2,3,4-tetrahydronaphthalene; D006632:Histamine; D010738:Type C Phospholipases; D011738:Pyrilamine