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Endothelin ET A and ET B mRNA and receptors expressed by smooth muscle in the human vasculature: majority of the ET A sub‐type
Author(s) -
Davenport Anthony P.,
O'Reilly Gillian,
Kuc Rhoda E.
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.tb13322.x
Subject(s) - aorta , receptor , vascular smooth muscle , endothelin receptor , artery , medicine , endothelin 1 , endocrinology , anatomy , pulmonary artery , chemistry , biology , smooth muscle
1 We measured the ratio of ET A and ET B sub‐types in the media (containing mainly smooth muscle) of human cardiac arteries (aorta, pulmonary and coronary), internal mammary arteries and saphenous veins. 2 In saturation experiments, [ 125 I]‐endothelin‐1 ([ 125 I]‐ET‐1) bound with high affinity to the media of each vessel ( n = 3 individuals or homogenate preparations ± s.e.mean): coronary artery, K D = 0.14 ± 0.02 n m , B max = 71.0 ± 21.0 fmol mg −1 protein; pulmonary artery, K D = 0.85 ± 0.25 n m , B max = 15.2 ± 10.3 fmol mg −1 protein; aorta, K D = 0.51 ± 0.02 n m , B max = 9.4 ± 4.4 fmol mg −1 protein; internal mammary artery, K D = 0.34 ± 0.31 n m , B max = 2.0 ± 0.5 fmol mg −1 protein and saphenous vein, K D = 0.28 ± 0.05 n m , B max = 52.8 ± 1.0 fmol mg −1 protein. In each vessel, over the concentration‐range tested, Hill slopes were close to unity and a one site fit was preferred to a two site model. 3 In competition binding assays, the ET A selective ligand, BQ123 inhibited the binding of 0.1 n m [ 125 I]‐ET‐1 to the media in a biphasic manner. In each case, a two site fit was preferred to a one or three site model: coronary artery, K D ET A = 0.85 ± 0.03 n m , K D ET B = 7.58 ± 2.27 μ m , ratio = 89:11%; pulmonary artery, K D ET A = 0.27 ± 0.05 n m , K D ET B = 24.60 ± 5.34 μ m , ratio = 92:8%; aorta, K D ET A = 0.80 ± 0.40 n m , K D ET B = 2.67 ± 2.60 μ m ratio = 89:11%; saphenous vein, K D ET A = 0.55 ± 0.17 n m , K D ET B = 14.4 ± 0.26 μ m , 85:15% ( n = 3 individuals or homogenate preparations ± s.e.mean). BQ123 showed up to 18000 fold selectivity for the ET A over the ET B sub‐type. The ET A ‐selective ligand, [ 125 I]‐PD151242 labelled 85% of the receptors detected by a fixed concentration of [ 125 I]‐ET‐1 in media of internal mammary artery, measured by quantitative autoradiography. In contrast, the density of ET B receptors detected with [ 125 I]‐BQ3020 was 7.0 ± 1.5 amol mm −2 , representing about 8% of [ 125 I]‐ET‐1. 4 A single band corresponding to the expected position for mRNA encoding the ET A receptor (299 base pairs) was found in the media in each of the five vessels ( n = 3 individuals) using reverse‐transcriptase polymerase chain reaction assays. A single band corresponding to the ET B sub‐type (428 base pairs) was also always detected. 5 35 S‐labelled antisense probes to ET A and ET B hybridised to the media of epicardial coronary arteries as well as intramyocardial vessels, confirming the presence of mRNA encoding both sub‐types in the vascular smooth muscle of the vessel wall. 6 Although mRNA for both receptors was detected, competition binding using BQ123 demonstrated that the majority (at least 85%) of ET receptors present in smooth muscle are the ET A sub‐type. These results provide further support for the hypothesis that the ET A sub‐type is the receptor that must be blocked in humans to produce a beneficial vasodilatation in pathophysiological conditions where there is an increase in peptide concentration or receptor density.