RT Journal Article
SR Electronic
T1 Binding and functional properties of endothelin receptor subtypes in the human prostate.
JF Molecular Pharmacology
JO Mol Pharmacol
FD American Society for Pharmacology and Experimental Therapeutics
SP 306
OP 311
VO 45
IS 2
A1 S Kobayashi
A1 R Tang
A1 B Wang
A1 T Opgenorth
A1 P Langenstroer
A1 E Shapiro
A1 H Lepor
YR 1994
UL http://molpharm.aspetjournals.org/content/45/2/306.abstract
AB The objective of the present study was to characterize the binding and functional properties of endothelin (ET) receptor subtypes in the human prostate. Human prostatic tissue was obtained from male subjects undergoing radical prostatectomy for low-volume prostate cancer. The optimal assay conditions for characterizing human prostatic ET-1 binding sites on slide-mounted tissue sections were defined. Maximal specific 125I-ET-1 binding was achieved after a 10-min preincubation, a 120-min incubation, and a washing procedure that consisted of a brief rinse and a 1-min wash. The mean equilibrium dissociation constant (Kd) and density (Bmax) of ET-1 binding sites determined from six saturation studies were 0.72 +/- 0.13 nM and 40.4 +/- 6.9 fmol/mg of wet weight, respectively. The mean Hill coefficient was 0.99 +/- 0.01, indicating that 125I-ET-1 identifies a single population of binding sites. The pharmacology of 125I-ET-1 binding sites was characterized using competitive binding experiments. The competition plots for ET-1 were best fit by a one-binding site model, whereas the plots for sarafotoxin 6C (S6C) and BQ123 were consistently best fit by a two-site model. The mean Ki value of ET-1 was 0.34 +/- 0.12 nM. The mean Ki values for the high and low affinity S6C binding sites were 0.50 +/- 0.09 nM and 0.84 +/- 0.28 microM, respectively. The mean Ki values for the high and low affinity BQ123 binding sites were 5.51 +/- 1.05 nM and 24.9 +/- 6.5 microM, respectively. The ratio of ETA to ETB binding sites was approximately 2:1. The ET receptor subtype mediating prostatic smooth muscle tension was investigated using agonist-antagonist competition studies. ET-1, a nonselective ET agonist, elicited a potent contraction of prostate smooth muscle. The pA2 of BQ123 for inhibiting ET-1-mediated contraction was 6.84. S6C, a selective ETB agonist, also elicited a potent contraction of prostate smooth muscle. BQ123 at concentractions between 0.1 and 10 microM did not shift the S6C dose-response curve. These functional studies suggest that both ETA and ETB receptors mediate the tension of prostate smooth muscle. Endogenous ETS may be involved in the pathophysiology of bladder outlet obstruction in men with benign prostatic hyperplasia. If this is the case, then ET antagonists may represent effective treatment for benign prostatic hyperplasia.