Abstract |
[(3)H] Tyr-Tic-(2S,3R)-beta-MePhe-Phe- OH (where Tic: 1,2,3,4- tetrahydroisoquinoline-3- carboxylic acid) with a specific radioactivity of 53.7 Ci/mmol was synthesized and characterized in receptor binding assays at 25 degrees C in rat brain membranes. The specific binding was saturable and displayed high affinity, with a K(D) of 0.16+/-0.005 nM and B(max) of 85.9+/-6.3 fmol/mg protein. NaCl increased its affinity by about 4-fold in membranes of rat brain and Chinese Hamster Ovary Cells stably transfected with the human delta-opioid receptors (hDOR-CHO) showing that the new ligand is an antagonist. The prototypic delta- opioid ligands were much more potent than mu- or kappa-specific ligands in competition assays. The autoradiographic distribution of the binding sites of the new ligand agreed with the known locations of the delta-opioid receptors in rat brain. The unlabeled new ligand was about 7-fold more potent than the parent peptide in competing for the binding sites of [(3)H] Tyr-Tic-(2S,3R)-beta-MePhe-Phe- OH in rat brain membranes. Likewise, the threo-beta-methyl analog was 3.8-fold more potent than the parent compound in antagonizing the effect of DPDPE in the [(35)S] GTPgammaS functional assay in hDOR-CHO membranes. The new, highly potent, conformationally constrained antagonist may be a valuable pharmacological tool in understanding the structural and topographical requirements of peptide ligand binding to the delta-opioid receptors.
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Authors | Erika Birkas, Istvan Kertesz, Geza Toth, Lidia Bakota, Karoly Gulya, Maria Szucs |
Journal | Neuropeptides
(Neuropeptides)
Vol. 42
Issue 1
Pg. 57-67
(Feb 2008)
ISSN: 0143-4179 [Print] Netherlands |
PMID | 18068762
(Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
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Chemical References |
- (3H)Tyr-Tic-(2S,3R)-beta-MePhe-Phe-OH
- Analgesics, Opioid
- Oligopeptides
- Radiopharmaceuticals
- Receptors, Opioid, delta
- Guanosine 5'-O-(3-Thiotriphosphate)
- Enkephalin, D-Penicillamine (2,5)-
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Topics |
- Analgesics, Opioid
(antagonists & inhibitors, pharmacology)
- Animals
- Autoradiography
- Binding Sites
- Brain Chemistry
(drug effects)
- CHO Cells
- Cricetinae
- Cricetulus
- Enkephalin, D-Penicillamine (2,5)-
(antagonists & inhibitors, pharmacology)
- Guanosine 5'-O-(3-Thiotriphosphate)
(pharmacology)
- Humans
- Male
- Oligopeptides
(chemical synthesis, pharmacology)
- Radioligand Assay
- Radiopharmaceuticals
(chemical synthesis, pharmacology)
- Rats
- Rats, Wistar
- Receptors, Opioid, delta
(antagonists & inhibitors)
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