[125I]-PD151242: a selective radioligand for human ETA receptors.
Our aim was to synthesize a new endothelin ETA selective radioligand, [125I]-PD151242 and characterize the compound in human vascular tissue. Binding of [125I]-PD151242 to sections of human aorta was time-dependent and reached equilibrium after 120 min at 23 degrees C with an association rate constant of 1.26 +/- 0.17 x 10(8) M-1 min-1 (n = 3 individuals +/- s.e.mean). The binding was reversible at 23 degrees C with an observed dissociation rate constant of 0.0025 +/- 0.0006 min-1 (n = 3). Saturation binding assays using [125I]-PD151242 revealed a single population of high affinity ET receptors (n = 3) in aorta (KD = 0.76 +/- 0.17 nM; Bmax = 5.98 +/- 1.56 fmol mg-1 protein), pulmonary (KD = 1.75 +/- 0.20 nM; Bmax = 12.78 +/- 1.39 fmol mg-1 protein) and coronary arteries (KD = 0.51 +/- 0.07 nM; Bmax = 44.9 +/- 1.67 fmol mg-1 protein). ETA selective ligands competed for [125I]-PD151242 binding in aorta with nanomolar affinity (BQ123, KD = 0.41 +/- 0.26 nM; FR139317, KD = 0.55 +/- 0.11 nM) whereas the ETB selective compound, BQ3020, competed with micromolar affinity (KD = 1.36 +/- 0.25 microM). In isolated coronary arteries, PD151242 was a functional antagonist and caused a significant, parallel rightward shift of the ET-1 dose-response curve with a pA2 value of 5.92 (n = 5) and a slope of unity. The high affinity and selectivity of [125I]-PD151242 for ETA receptors will facilitate the characterization of this sub-type in human tissues.
Clinical Pharmacology Unit, University of Cambridge, Addenbrooke's Hospital.
A P
AP
Davenport
R E
RE
Kuc
F
F
Fitzgerald
J J
JJ
Maguire
K
K
Berryman
A M
AM
Doherty
D000328:Adult; D000595:Amino Acid Sequence; D001011:Aorta / Q000378:metabolism; D001158:Arteries / Q000187:drug effects / Q000378:metabolism*; D001381:Azepines / Q000378:metabolism* / Q000494:pharmacology; D001667:Binding, Competitive; D003331:Coronary Vessels / Q000378:metabolism; D065128:Endothelin Receptor Antagonists; D016232:Endothelins / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007211:Indoles / Q000378:metabolism; D007457:Iodine Radioisotopes; D008875:Middle Aged; D009842:Oligopeptides / Q000378:metabolism* / Q000494:pharmacology; D010446:Peptide Fragments / Q000378:metabolism; D010456:Peptides, Cyclic / Q000378:metabolism; D011651:Pulmonary Artery / Q000378:metabolism; D011869:Radioligand Assay; D017466:Receptors, Endothelin / Q000378:metabolism*
D001381:Azepines; D065128:Endothelin Receptor Antagonists; D016232:Endothelins; D007211:Indoles; D007457:Iodine Radioisotopes; D009842:Oligopeptides; D010446:Peptide Fragments; D010456:Peptides, Cyclic; D017466:Receptors, Endothelin; C079574:FR 139317; C075771:BQ 3020; C087850:PD 151242; C072247:cyclo(Trp-Asp-Pro-Val-Leu)