Specific Endothelin Receptor Research Articles

Characterization of renal glomerular endothelin receptors in the rat

Specific receptors for Endothelin (Et) have been identified in the glomerulus of rat kidney. Human 125I-ET binds to a single population of high affinity receptors in glomerular membranes from normal rats with a mean equilibrium dissociation constant of 200 pM. The binding was time and temperature-dependent, saturable and reversible. The Et-receptor complex was not affected by either vasopressin, atrial natriuretic factor or angiotension II.

Identification of two types of specific endothelin receptors in rat mesangial cell

Two types of receptors specific for endothelin were identified using cross-linking technique in cultured rat mesangial cells. The molecular weights of these receptors were approximately 58,000 and 34,000 by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate. The binding of radio-iodinated-endothelin to its receptors was inhibited by excess of unlabeled endothelin, but not by nifedipine, nicardipine, verapamil, diltiazem, angiotensin II or [Arg 8]-vasopressin. The endothelin binding proteins were solubilized with 1% digitonin and fractionated under non-denaturing conditions by gel filtration. Two endothelin binding peaks eluted at the positions corresponding to the molecular weights of 65,000 and 43,000. These observations indicate that there are two types of specific endothelin receptors in rat mesangial cells which are distinct from voltage dependent L-type calcium channel.

Specific receptor for endothelin in cultured rat cardiocytes

Specific binding sites for the endothelium-derived vasoconstrictor endothelin (ET) and its effect on cytosolic free Ca2+ concentrations [( Ca2+]i) were studied in a primary culture of cardiocytes from neonatal rats. Binding studies using 125I-labeled-porcine ET as a radioligand revealed the presence of a single class of high-affinity binding sites for ET in cardiocytes with an apparent Kd of 6-9 x 10(-10) M and a Bmax of 50,000-80,000 sites/cell. Neither various vasoconstrictors nor Ca2+-channel blockers affected the binding. Pretreatment with ET substantially reduced the total number of ET receptors without changing their affinity. ET dose-dependently increased [Ca2+]i in fura-2-loaded cardiocytes. These data indicate that cardiocytes have specific ET receptors that are controlled by a down-regulation mechanism, and that ET induces a receptor-mediated increase in [Ca2+]i in cardiocytes.

Specific receptors for endothelin on membranes from human placenta. Characterization and use in a binding assay

High-affinity binding sites for endothelin have been found in a human placenta membrane preparation. 125I-endothelin bound to placenta membranes at 20° C with an association half-time of 30 min, whereas the binding was only slowly reversed with a dissociation half-time of 250 min. In saturation experiments, a single class of high-affinity binding sites was identified with an apparent dissociation constant (K D) of 24 pM and a maximal density of 240 fmol per mg of protein. The binding of 123I-endothelin was half-maximally inhibited by cold endothelin at a concentration (IC 50) of 140 pM. In contrast, no inhibition was found at 10 −4 M for a variety of vasoactive peptides such as angiotensin II, vasopressin, neuropeptide Y, substance P, CGRP, bradykinin, leucine enkephalin or dynorphin A. Similarly, the binding was modulated neither by the calcium channel blockers nifedipine, verapamil or diltiazem, nor by the calcium channel agonist Bay k 8644. There was also no effect with the structurally-related bee venom apamin. Using this membrane preparation, endothelin-like activity could be measured in the medium of cultured human endothelial cells by competition binding technique.