Distribution of endothelin-1-receptor subtypes in rat portal vein
Filippelli, A.; Falciani, M.; Palla, A.; D'Amico, M.; Vacca, C.; Rossi, F.
Journal of Cardiovascular Pharmacology 27(1): 113-118
1996
ISSN/ISBN: 0160-2446 PMID: 8656643 Document Number: 465525
Endothelin-1 (ET-1), a potent vasoactive peptide, was first isolated from cultured porcine endothelial cells. Subsequent studies revealed the existence of two additional related peptides, ER-2 and ER-3, and at least two distinct ET-receptor subtypes, ET-A (selective for ET-1) and ET-B (nonselective for ET isopeptides). These isopeptides and receptors are widely distributed in many tissues and are involved in numerous biological responses. the aim of this study was to identify the eventual distribution of the two distinct endothelin-receptor subtypes in isolated endothelium-denuded rat portal vein rings (PVRs) and strips (PVSs). BQ-123 (0.6, 1, and 6 mu-M) and PD-145065 (0.06, 0.1, 0.6, and 6 mu-M) were used to differentiate the subtypes because they are selective antagonists for ER-A and nonselective antagonists for ET-A-ET-B receptors, respectively. To characterize the ET receptors further, sarafotoxin-S6c (a selective ET-B-receptor agonist) and IRL-1038 (a selective ET-B-receptor antagonist) were used. In PVRs, cumulative additions of ET-1 (0.1-100 nM) caused graded and slow contractions and potentiated spontaneous rhythmic contractions. The EC-50 values and maximal response to 100 nM of ET-1 were 2.72 nM and 0.75 g, respectively (n = 7). PVSs showed ET-1 EC-50 values very similar to those of PVRs but E-max values to 100 nM of ET-1 were significantly lower (E-max = 0.33 g; n = 7). Moreover, ET-1 clearly increased the amplitude and frequency of spontaneous contractions in both types of specimens, although these were greater in the PVSs. Thirty-minute incubation with the selective ET-A-receptor antagonist BQ-123 blunted ET-1-induced effects in PAS specimens but only weakly antagonized ET-1-induced contractions in PVRs. In contrast, the nonselective ET-A-ET-B-receptor antagonist PD-145065 significantly shifted the ET-1 concentration-response curve to the right in PVRs and partially inhibited ET-1 effects in PVSs. Moreover, sarafotoxin-S6c (0.1-100 nM) contracted PVRs and PVSs in a similar manner to ET-1; its effects were antagonized by IRL-1038 only at the PVR level. The differences observed in PVR and PAS specimens in response to agonists and antagonists of ET confirmed the great heterogeneity of endothelin-sarafotoxin receptors. In our experimental models, functionally ET-B-like (or non-ET-A) receptors seem mostly to mediate vasoconstriction.