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Selectivity of [ 125 I]‐PD 151242 for human, rat and porcine endothelin ET A receptors in the heart
Author(s) -
Peter Markus G.,
Davenport Anthony P.
Publication year - 1995
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.1476-5381.1995.tb13226.x
Subject(s) - receptor , ventricle , dissociation constant , binding site , radioligand , population , ligand (biochemistry) , antagonist , chemistry , endothelin receptor , stereochemistry , biology , microbiology and biotechnology , biophysics , medicine , biochemistry , environmental health
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 ET A ‐selective antagonist PD151242 in heart tissues derived from man, rat and pigs by use of radioligand binding techniques. 2 Binding of [ 125 I]‐PD151242 to sections of human left ventricle was time‐dependent and reached equilibrium after 120 min at 23°C with an association rate constant of 0.0235 min −1 n m −1 . The binding was reversible at 23°C with a dissociation rate constant of 0.00144 min −1 . 3 Saturation binding assays with [ 125 I]‐PD151242 revealed a single population of high affinity ET receptors in human left ventricle ( K D = 1.07 ± 0.08 n m ; B max = 29.8 ± 4.2 fmol mg −1 protein), porcine left ventricle ( K D = 1.92 ± 0.27 n m ; B max = 493 ± 248 fmol mg −1 protein), and rat heart ( K D = 0.64 ± 0.08 n m ; B max = 82.34.7 fmol mg −1 protein). 4 Unlabelled PD151242 competed with specific [ 125 I]‐ET‐1 binding to human left ventricle tissue in a biphasic manner with high affinity binding to the ET A ‐site ( K D = 7.21 ± 2.83 n m ) and lower affinity for the ET B ‐subtype ( K D = 104 ± 23 μ m ), indicating a greater than 10000 fold selectivity to the high affinity site. 5 The ET A ‐selective ligand FR139317 competed for [ 125 I]‐PD151242 binding in human left ventricle with nanomolar affinity ( K D = 0.37 ± 0.10 n m ), whereas the ET B ‐selective compound, BQ3020, competed with only micromolar affinity ( K D = 1.5 ± 0.26 μ m ). 6 The novel ET A ‐selective radioligand [ 125 I]‐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 ET A ‐subtype making [ 125 I]‐PD 151242 a useful selective radioligand for further characterization of the ET A ‐receptor in human tissue.