Specific Endothelin-1 Binding Research Articles

Binding of a new bioactive 31-amino-acid endothelin-1 to an endothelin ET B or ET B-like receptor in porcine lungs

Endothelin-1-(1–31) is a new bioactive 31-amino-acid-length peptide generated from big endothelin-1 by chymase or other chymotrypsin-type proteases with various pathophysiologic functions. In this study, we have detected the specific and monophasic binding of [ 125I]endothelin-1-(1–31) in porcine lung membranes. Competition studies of [ 125I]endothelin-1-(1–31) binding by unlabeled endothelin-1-(1–31), endothelin-1, endothelin-3, and antagonists and agonists of endothelin ET A and ET B receptors suggest that the binding protein is an endothelin ET B or ET B-like receptor rather than an endothelin ET A receptor in porcine lungs. Kinetic studies showed that the affinity of endothelin-1-(1–31) to its receptor was approximately one order of magnitude lower than that of endothelin-1, and that the specific binding of endothelin-1-(1–31) was about 19% of endothelin-1 binding. The binding of [ 125I]endothelin-1-(1–31) was extremely slow, slower even than that of endothelin-1, and nearly irreversible. This unique quasi-irreversibility may explain the slow-onset and long-lasting biologic effects of this peptide in vivo.

Presence and localization of endothelin receptor in the rat ovary and its regulation by pituitary gonadotropins.

In the present study we examined the regulation of receptors for endothelin 1 (ET-1) in rat granulosa cells. We examined the localization and regulation of ET receptors in immature rat ovary and the effects of ET-1 on steroidogenesis in cultured rat granulosa cells. The ovaries used in autoradiography were derived from pregnant mare serum gonadotropin and human chorionic gonadotropin-treated immature rats. Granulosa cells were obtained from diethylstilbestrol-treated immature rats and incubated with 125I-ET-1. Granulosa cells were cultured with ET-1 in the presence or absence of ovine follicle-stimulating hormone. The concentrations of sex steroid hormones in conditioned media were measured by radioimmunoassay. The binding site for ET-1 was localized in the granulosa cells, but not in thecal and luteal cells. Follicle-stimulating hormone (FSH) induced a dose-dependent increase in specific binding for ET-1 to cultured rat granulosa cells. In contrast, luteinizing hormone (LH) induced a dose-dependent decrease in specific binding for ET-1 to cultured rat granulosa cells. Conversely, treatment with prolactin and several sex steroid hormones had no effects on the specific binding of ET-1. Treatment with ET-1 inhibited FSH-stimulated accumulation of progesterone and estradiol in cultured rat granulosa cells. The results indicate that both FSH and LH influence the expression of ET-1 receptor, and that ET-1 may play a regulatory role in the ontogeny of the granulosa cell.

Is endothelin-1 release at reperfusion of the ischaemic human heart due to cold-induced displacement of endothelin from binding sites?

Following reperfusion of ischaemic human hearts subjected to cold (4° C) cardioplegia during coronary bypass surgery, there was an increase in cardiac outflow of endothelin-1 but not the pro-peptide big endothelin-1. Furthermore, specific endothelin-1 binding in human lung membrane preparations was displaced by incubation in buffer medium at 4° C. The present results thus indicate that cold-induced displacement of endothelin-1 binding, rather than increased synthesis, may explain the cardiac release of endothelium-1 following ischaemia during heart surgery in which cold cardioplegia has been used.

Specific binding of endothelin-1 to canine tracheal epithelial cells in culture.

We have studied the binding of endothelin-1 (ET-1) to cultured canine tracheal epithelial cells. A single specific binding site for 125I-labeled ET-1 was identified with an apparent dissociation constant (Kd) of 0.2 nM, maximal binding sites (Bmax) of 6.7 x 10(3) sites/cell, and half-maximal inhibition (IC50) of 0.3 nM during a 2-h incubation period. The binding of 125I-ET-1 to these cells was inhibited by the presence of unlabeled ET-1, ET-2, or BQ-123, whereas ET-3 and sarafotoxin S6c did not compete for this binding site. These binding characteristics are consistent with those of the ETA receptor. At 37 degrees C, specific binding continuously increased over 18 h, while at 4 degrees C, it reached a plateau by 2 h. The increase in binding at 37 degrees C was not associated with DNA synthesis but was dependent upon protein synthesis, suggesting that epithelial binding sites were produced continuously under these incubation conditions. Our results indicate that canine tracheal epithelial cells possess specific binding sites for ET-1 with characteristics similar to those of the ETA receptor subtype. Because these cells are demonstrated to both release and bind ET-1, the results further suggest that ET-1 is involved in paracrine and/or autocrine control mechanisms in the airway epithelium.

Desensitization of endothelin-1 binding by vasopressin via a cAMP-mediated pathway in rat CCD.

In renal collecting ducts, endothelin-1 (ET-1) inhibits Na+ reabsorption and antagonizes the effects of arginine vasopressin (AVP). Whether AVP may affect ET-1 action in the collecting ducts that mainly express the ETB receptor subtype, however, remains unknown. Since ETB, but not ETA, possesses a consensus amino acid sequence for possible phosphorylation by protein kinase A (PKA), we hypothesized that AVP may influence ET-1 binding to the ETB receptor via PKA. In microdissected rat cortical collecting ducts, the specific ET-1 binding decreased by 35% (15.6 +/- 4.4 vs. 24.0 +/- 3.6 amol/mm in control) following 20-min preincubation with 10(-7) M AVP. This decrease in ET-1 binding was mimicked by 10(-5) M forskolin and by 10(-4) M dibutyryl (DB) adenosine 3',5'-cyclic monophosphate (cAMP), indicating that this heterologous desensitization may be caused by a cAMP-dependent mechanism. Moreover, N-(2([3-(4-bromophenyl)-2-propenyl]-amino]-ethyl)-5- isoquinolinesulfonamide (H-89) and the Rp diastereoisomer of cAMP, Rp-cAMPS, which are both PKA-specific inhibitors, eliminated AVP-induced ETB receptor desensitization. The reduction in ET-1 binding was characterized by a decrease in binding affinity [dissociation constant (Kd) = 4 vs. 2 nM in control] with no change in maximal binding capacity. In contrast, forskolin and DBcAMP had no effect on ET-1 binding in endothelium-denuded aortic strips, which mainly express ETA subtype. These results showed that AVP rapidly downregulates the ETB receptor by reducing Kd through a PKA-dependent pathway. Thus ET-1 and AVP may act in a mutually antagonizing manner in the renal collecting ducts.

Evidence of Glycosylated Sites on the Endothelin-1 Receptor in Swiss 3T3 Cells

The effects of incubation of intact cells with six different lectins on the specific binding of [125I]endothelin-1 (ET-1) were determined in Swiss 3T3 fibroblasts. ET-1 binding was unaffected by pretreatment of cells for 1 h at 37 degrees C with concanavalin A, soybean agglutinin, Ulex europaeus agglutinin I, peanut agglutinin, or Galanthus nivalis agglutinin. However, preincubation of cells with 300 micrograms/ml of wheat germ agglutinin resulted in a 70% decrease in specific binding of ET-1 to cell-surface receptors. The inhibitory effects of wheat germ agglutinin were diminished by brief incubation of lectin-treated cells with 100 mM N-acetylglucosamine, a monosaccharide specifically recognized by wheat germ agglutinin. Neither glucose nor mannose had any effect on wheat germ agglutinin-mediated inhibition of the specific binding of ET-1. These results suggest that the ET-1 receptor on 3T3 cells is a glycoprotein that contains one or more N-acetylglucosamine residues at or near the ligand binding site.

Autoradiographic Localization of Endothelin-1 Binding Sites in Porcine Skin

Autoradiographic techniques and 125I-labeled endothelin-1 were used to study the distribution of endothelin-1 binding sites in porcine skin. Specific endothelin-1 binding sites were localized to blood vessels (capillaries, deep cutaneous vascular plexus, arteries, and arterioles), the deep dermal and connective tissue sheath of hair follicles, sebaceous and sweat glands, and arrector pili muscle. Specific binding was inhibited by endothelin-2 and endothelin-3 as well as endothelin-1. Non-specific binding was found in the epidermis and the medulla of hair follicles. No binding was found in connective tissue or fat. These vascular binding sites may represent endothelin receptors, in keeping with the known cutaneous vasoconstrictor actions of the peptide. If all binding sites are receptors, the results suggest that endothelin could also regulate the function of sweat glands and may have trophic effects in the skin.