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[ 125 I]‐PD151242: a selective ligand for endothelin ET A receptors in human kidney which localizes to renal vasculature
Author(s) -
Davenport Anthony P.,
Kuc Rhoda E.,
Hoskins Sarah L.,
Karet Fiona E.,
Fitzgerald Fiona
Publication year - 1994
Publication title -
british journal of pharmacology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.432
H-Index - 211
eISSN - 1476-5381
pISSN - 0007-1188
DOI - 10.1111/j.1476-5381.1994.tb17140.x
Subject(s) - receptor , endothelin receptor , binding site , endothelins , kidney , endothelin 1 , medicine , agonist , radioligand assay , population , ligand (biochemistry) , endocrinology , radioligand , chemistry , tetrapeptide , endothelin 3 , biology , microbiology and biotechnology , stereochemistry , biochemistry , peptide , environmental health
1 The linear tetrapeptide radioligand, [ 125 I]‐PD151242 was used to characterize ET A receptors in human kidney which is an ET B ‐rich tissue. Saturation binding assays with [ 125 I]‐PD151242 revealed a single population of high affinity endothelin receptors: K D = 0.75 ± 0.07 n m and B max = 48.4 ± 1.6 fmol mg −1 protein ( n = 3 individuals ± s.e.mean). Hill slopes were close to unity and a one site fit was preferred to a two site model. 2 ET A ‐receptor‐selective ligands competed for [ 125 I]‐PD151242 binding with sub‐nanomolar affinity: BQ123 K D = 0.43 ± 0.10 n m , B max = 46.6 ± 7.9 fmol mg −1 protein; FR139317, K D = 0.37 ± 0.06nM, B max = 39.5 ± 6.5 fmol mg −1 protein ( n = 3 individuals ± s.e.mean). In each case, monophasic inhibition curves were obtained and a one site fit was preferred to a two site model. The ET B ‐selective agonist, BQ3020 at the highest concentration tested (10 μ m ) inhibited binding by only 50%. The non‐selective RO462005 competed for the binding of [ 125 I]‐PD151242: K D = 1.31 ± 1.38 μ m , B max = 33.0 ± 9.7 fmol mg −1 protein. Endothelin‐2 and sarafotoxin S6B inhibited [ 125 I]‐PD151242 binding to renal tissue whereas ET‐3 and sarafotoxin S6C were less effective. Non‐endothelin and non‐sarafotoxin peptides did not compete. 3 No degradation of [ 125 I]‐PD151242 was detected following incubation of the ligand with renal tissue under the conditions of the binding assay. 4 Polymerase chain reaction products corresponding to the expected size for mRNA encoding ET A and ET B receptor sub‐types were detected in cortex and medulla in each of the five individuals examined. 5 Autoradiographical studies showed that ET A receptors visualised with [ 125 I]‐PD151242 were mainly localized to blood vessels including interlobular and arcuate arteries, arterioles and adjacent arcuate veins. ET B receptors localized with [ 125 I]‐BQ3020 were concentrated in the medulla and the density of binding to vessels was low. 6 These data suggest [ 125 I]‐PD151242 is selective for ET A receptors in human kidney and this sub‐type is mainly localized to the renal vasculature. The results provide further evidence that the human vasculature mainly expresses the ET A receptor.