title: Determination of the drug-receptor dissociation constant of endothelin-1 using photorelaxation of rabbit isolated thoracic aorta.
abstract: An in vitro preparation of rabbit thoracic aorta was tested in order to determine whether isometric contractile force induced by endothelin-1 (ET-1) in this preparation is changed when the tissue is exposed to ultraviolet (UV) light. After constriction of an aortic segment to a steady-state level of tension with ET-1, a flash of UV light induced a transient decrease in tension that returned exponentially to equilibrium. This response was endothelium-independent and sensitive to the extracellular sodium concentration. The rate of return to the baseline tension after photorelaxation increased with increasing concentrations of ET-1. UV light had only a slight photorelaxing effect at very low and very high ET-1 concentrations and a much larger effect at concentrations near the A50 value of ET-1. Since an irreversible antagonist does not yet exist for ET-1, the partial irreversible blockade method for getting the dissociation constant (KD) functionally was not possible. The relaxation method, using UV light as a perturbation of ligand-receptor equilibrium, was used instead to obtain KD as well as the forward (k1) and reverse (k2) rate constants of ET-1 in this tissue.
authors.affiliation: Department of Pharmacology, Temple University School of Medicine, Philadelphia, PA 19140.
authors.forename: L O
authors.initials: LO
authors.lastname: Nordberg
authors.forename: R B
authors.initials: RB
authors.lastname: Raffa
authors.forename: R J
authors.initials: RJ
authors.lastname: Tallarida
mesh_terms: D000818:Animals; D001013:Aorta, Thoracic / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D016232:Endothelins / Q000378:metabolism* / Q000494:pharmacology; D005260:Female; D066298:In Vitro Techniques; D011817:Rabbits; D017466:Receptors, Endothelin / Q000378:metabolism; D014466:Ultraviolet Rays; D014661:Vasoconstriction / Q000187:drug effects / Q000528:radiation effects
chemical_list: D016232:Endothelins; D017466:Receptors, Endothelin