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Characterization of the binding of endothelin ET B selective ligands in human and rat heart
Author(s) -
Russell Fraser D.,
Davenport Anthony P.
Publication year - 1996
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.1476-5381.1996.tb15720.x
Subject(s) - ventricle , receptor , endothelin receptor , medicine , endocrinology , chemistry , endothelins , ligand (biochemistry) , endothelin 1 , biology
1 We determined competition binding characteristics of endothelin ET B receptor selective ligands in human left ventricle and compared these values to those obtained with rat left ventricle. Sarafotoxin S6c, ET‐3, BQ788 and IRL2500 competed against [ 125 I]‐BQ3020 (ET B selective radioligand; Molenaar et al ., 1992) with high affinity and against [ 125 I]‐PD151242 (ET A selective radioligand) with low affinity in human left ventricle, confirming the ET B selectivity of these compounds. 2 ET‐3 competed with moderate selectivity for ET B over ET A receptors in human left ventricle and with slightly higher selectivity in rat left ventricle (460 and 1,400 fold, respectively). There was a small difference in the affinity of ET A receptors for ET‐3 ( K D ET A in human left ventricle = 0.07 ± 0.02 μ m ; K D ET A in rat left ventricle = 0.27 ± 0.08 μ m ; P = 0.05) but no difference in the affinity of ET B receptors for this ligand ( K D ET B in human left ventricle = 0.15 ± 0.06 nM; K D ET B in rat left ventricle = 0.19 ± 0.03 nM). 3 The selectivity of sarafotoxin S6c for ET B over ET A receptors in human left ventricle was 5,900 fold compared with 59,400 fold in rat left ventricle. The affinity of ET A receptors for sarafotoxin S6c was higher in human than in rat left ventricle ( K D ET A = 2.00 ± 0.20 μ m and 3.50 ± 0.26 μ m , respectively; P = 0.03), while the affinity of ET B receptors for this ligand was higher in rat left ventricle ( K D ET B = 0.06 ± 0.02 nM) than in human left ventricle ( K D ET B = 0.34 ± 0.13 nM) ( P = 0.02). The affinity of ET B receptors for sarafotoxin S6c in rat left ventricle determined in the absence or presence of GTP was the same indicating that differing affinity states of ET B receptors in human and rat left ventricle do not account for the variation observed between species. 4 There was no difference in the affinity of ET A receptors for BQ788 ( K D ET A = 1.01 ± 0.20 μ m and K D ET A = 1.39 ± 0.35 μ m ) or for the novel ET B selective antagonist, IRL2500 ( K D ET A = 30.0 ± 20.8 μ m and K D ET A = 55.6 ± 9.93 μ m ) in human and rat left ventricle, respectively. ET B receptors had a significantly higher affinity for BQ788 ( K D ET B = 9.8 ± 1.3 nM and K D ET B = 31.0 ± 5.4 nM; P = 0.02) and IRL2500 ( K D ET B = 78.2 ± 9.7 nM and K D ET B = 300.0 ± 75.1 nM; P = 0.03) in human and rat left ventricle, respectively. The synthetically synthesized ET B selective antagonist RES‐701‐1 (0.1–3 μ m ) failed to inhibit [ 125 I]‐ET‐1 binding in either tissue. 5 In conclusion, we have compared equilibrium dissociation constants for a number of ET B selective compounds in human and rat heart. The affinity of ET B receptors for sarafotoxin S6c, BQ788 and IRL2500 differed in human and rat left ventricle. No difference in affinity was detected for ET‐3 binding at ET B receptors. Sarafotoxin S6c binding was unaffected by GTP indicating that the different receptor affinities in human and rat heart cannot be explained by differing ET B receptor affinity states. This study highlights the need to consider differences in binding characteristics that may arise from the use of tissues obtained from different species.