A novel radioligand [125I]BQ-3020 selective for endothelin (ETB) receptors.
A linear endothelin (ET) analog, N-acetyl-LeuMetAspLysGluAlaValTyrPheAlaHisLeu-AspIleIleTrp (BQ-3020), is highly selective for ETB receptors. BQ-3020 displaces [125I]ET-1 binding to ETB receptors (nonselective to ET isopeptides) in porcine cerebellar membranes (IC50: 0.2nM) at a concentration 4,700 times lower than that to ETA receptors (selective to ET-1) on aortic vascular smooth muscle cells (VSMC) (IC50: 940nM). BQ-3020 as well as ET-1 and ET-3 elicits vasoconstriction in the rabbit pulmonary artery. The ETA antagonist BQ-123 failed to inhibit this BQ-3020-induced vasoconstriction. Furthermore, BQ-3020 elicits endothelium-dependent vasodilation. These data indicate that BQ-3020 has ETB agonistic activity. The radioligand [125I]BQ-3020 binds to cerebellar membranes at single high affinity sites (Kd = 34.4pM), whereas it scarcely binds to VSMC. [125I]BQ-3020 binding to the cerebellum was displaced by BQ-3020, ET-1 and ET-3 in a nonselective manner (IC50: 0.07-0.17nM). However, the binding of [125I]BQ-3020 was insensitive to the ETA antagonist BQ-123 and other bioactive peptides. Both [125I]ET-1 and [125I]BQ-3020 show slow onset and offset binding kinetics to ETB receptors. These data indicate that the radioligand [125I]BQ-3020 selectively labels ETB receptors and that the slow binding kinetics of ET-1 are dependent on the peptide sequence from Leu6 to Trp21, but not on the structure formed by its two disulfide bridges.
Ihara
M
M
Tsukuba Research Institute, Banyu Pharmaceutical Co., Ltd., Japan.
Saeki
T
T
Fukuroda
T
T
Kimura
S
S
Ozaki
S
S
Patel
A C
AC
Yano
M
M
D000595:Amino Acid Sequence; D000818:Animals; D001013:Aorta, Thoracic; D002531:Cerebellum / Q000187:drug effects; D016232:Endothelins / Q000494:pharmacology*; D004730:Endothelium, Vascular / Q000187:drug effects; D007457:Iodine Radioisotopes; D007700:Kinetics; D008969:Molecular Sequence Data; D009131:Muscle, Smooth, Vascular / Q000187:drug effects; D010446:Peptide Fragments / Q000494:pharmacology*; D010455:Peptides / Q000494:pharmacology*; D011817:Rabbits; D011869:Radioligand Assay; D011956:Receptors, Cell Surface / Q000187:drug effects*; D017466:Receptors, Endothelin; D013552:Swine; D014661:Vasoconstriction / Q000187:drug effects
D016232:Endothelins; D007457:Iodine Radioisotopes; D010446:Peptide Fragments; D010455:Peptides; D011956:Receptors, Cell Surface; D017466:Receptors, Endothelin; C075771:BQ 3020