S. Mihara et al., BINDING CHARACTERIZATION OF [H-3]S-0139, AN ANTAGONIST OF THE ENDOTHELIN ETA-RECEPTOR SUBTYPE, European journal of pharmacology, 342(2-3), 1998, pp. 319-324
S-0139 arboxy-acryloylamino)-5-hydroxyphenyl]-acryloyloxy myricerone,
sodium salt) is a highly specific nonpeptide endothelin ETA receptor a
ntagonist. The binding of [H-3]S-0139 was compared to that of [I-125]e
ndothelin-1 to characterize the binding of the antagonist in porcine a
ortic smooth muscle membranes. Scatchard analysis revealed a single cl
ass of [H-3]S-0139 binding sites with a K-d value of 0.61 +/- 0.10 nM
and a B-max of 0.72 +/- 0.16 pmol/mg protein. These sites were saturab
le and reversible. [I-125]Endothelin-1 also showed binding with high a
ffinity (K-d = 0.12 +/- 0.02 nM) to a homogenous population of binding
sites, whose B-max (0.71 +/- 0.20 pmol/mg protein) was almost the sam
e as that for [H-3]S-0139. In both cases, the binding could be displac
ed by known endothelin receptor ligands and their IC50 values in each
case showed a very close correlation (r = 0.986). The potency of seven
endothelin receptor antagonists to displace [H-3]S-0139 binding also
correlated highly to the potency for inhibiting the endothelin-1-induc
ed increase in cytosolic Ca2+ concentration (r = 0.949). Myriceric aci
d A showed a more potent functional activity than expected from its bi
nding affinity, but this seemed to result from the different assay con
ditions, such as incubation time. Together, the results suggest that S
-0139 labels only endothelin ETA receptor binding sites in porcine aor
tic smooth muscle. (C) 1998 Elsevier Science B.V.