Recent evidence suggests a role for endothelin (ET) in contraction of human prostate [J. Urol. 149:495-499 (1993)]. Although both ETA and ETB receptors have been shown to mediate contraction of smooth muscle, the molecular identity of the contractile ETB receptor is controversial. The aim of this study was to examine the receptor subtype that mediates ET-induced contraction in prostate from patients with benign prostatic hyperplasia. Saturation binding with 125I-ET-1 and 125I-ET-3 in prostate stromal cells (PSC) indicated the presence of receptors with subnanomolar affinity for these radioligands, with equivalent receptor densities. Inhibition of specific 125I-ET-1 or 125I-ET-3 binding in PSC revealed a rank order of potency of ET-1 - ET-3 = sarafotoxin S6c >> BQ-123. These data are consistent with a predominance of ETB receptors in PSC. The functional effects of ET stimulation of PSC were examined in a collagen gel contraction assay. ET-1 and ET-3 caused contraction of underlying collagen gel matrices with EC50 values of 0.4 +/- 0.04 and 0.7 +/- 0.2 nM, respectively. To determine the molecular nature of the contractile ETB receptor in PSC, reverse transcription-polymerase chain reactions were conducted with oligonucleotide primers to the 5' and 3' ends of the coding sequence of the full length human ETB receptor. DNA sequence analysis of the 1.3-kilobase DNA product showed 99% homology to other human ETB receptor cDNAs. The encoded protein has a deduced amino acid sequence identical to that of other human ETB receptors, with the exception of two conservative substitutions. Expression of the PSC ETB cDNA in COS-7 cells resulted in a binding profile similar to that observed in parent cells. Polymerase chain reaction analysis revealed the presence of prepro-ET-1 mRNA in PSC. Collectively, these data indicate that PSC from patients with benign prostatic hyperplasia express ETB receptors that mediate ET-induced contraction.