title: Selectivity of [125I]-PD151242 for human, rat and porcine endothelin ETA receptors in the heart.
abstract: 1. Endothelin-1 binds with high affinity to heart where it acts as a potent positive inotropic agent. Our aim was to characterize the labelled and unlabelled ETA-selective antagonist PD151242 in heart tissues derived from man, rat and pigs by use of radioligand binding techniques. 2. Binding of [125I]-PD151242 to sections of human left ventricle was time-dependent and reached equilibrium after 120 min at 23 degrees C with an association rate constant of 0.0235 min-1 nM-1. The binding was reversible at 23 degrees C with a dissociation rate constant of 0.00144 min-1. 3. Saturation binding assays with [125I]-PD151242 revealed a single population of high affinity ET receptors in human left ventricle (KD = 1.07 +/- 0.08 nM; Bmax = 29.8 +/- 4.2 fmol mg-1 protein), porcine left ventricle (KD = 1.92 +/- 0.27 nM; Bmax = 493 +/- 248 fmol mg-1 protein), and rat heart (KD = 0.64 +/- 0.08 nM; Bmax = 82.34.7 fmol mg-1 protein). 4. Unlabelled PD151242 competed with specific [125I]-ET-1 binding to human left ventricle tissue in a biphasic manner with high affinity binding to the ETA-site (KD = 7.21 +/- 2.83 nM) and lower affinity for the ETB-subtype (KD = 104 +/- 23 microM), indicating a greater than 10000 fold selectivity to the high affinity site. 5. The ETA-selective ligand FR139317 competed for [125I]-PD151242 binding in human left ventricle with nanomolar affinity (KD = 0.37 +/- 0.10 nM), whereas the ETB-selective compound, BQ3020, competed with only micromolar affinity (KD = 1.5 +/- 0.26 microM). 6. The novel ETA-selective radioligand [125I]-PD151242 binds with high affinity to human, rat and porcine heart. In human tissue, binding was shown to be reversible and highly selective for the ETA-subtype making [1251]-PD151242 a useful selective radioligand for further characterization of the ETA-receptor in human tissue.
authors.affiliation: Clinical Pharmacology Unit, University of Cambridge, Addenbrooke's Hospital.
authors.forename: M G
authors.initials: MG
authors.lastname: Peter
authors.forename: A P
authors.initials: AP
authors.lastname: Davenport
mesh_terms: D000328:Adult; D000818:Animals; D001381:Azepines / Q000494:pharmacology*; D001667:Binding, Competitive / Q000187:drug effects; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000494:pharmacology; D006321:Heart / Q000187:drug effects*; D006352:Heart Ventricles / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000494:pharmacology; D007457:Iodine Radioisotopes; D008024:Ligands; D008297:Male; D008875:Middle Aged; D009206:Myocardium / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology*; D010446:Peptide Fragments / Q000494:pharmacology; D051381:Rats; D017207:Rats, Sprague-Dawley; D013045:Species Specificity; D013552:Swine
chemical_list: D001381:Azepines; D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D007211:Indoles; D007457:Iodine Radioisotopes; D008024:Ligands; D009842:Oligopeptides; D010446:Peptide Fragments; C079574:FR 139317; C075771:BQ 3020; C087850:PD 151242