Scintillation proximity assay: competitive binding studies with [125I]endothelin-1 in human placenta and porcine lung

• Published in: Journal of cardiovascular pharmacology Vol. 17 Suppl 7; p. S143
• Main Authors: Berry, J A, Burgess, A J, Towers, P
• Format: Journal Article
• Language: English
• Published: United States 1991
• Subjects: Animals; Binding, Competitive; Endothelins - metabolism; Female; Humans; Iodine Radioisotopes; Lung - metabolism; Microspheres; Placenta - metabolism; Pregnancy; Receptors, Cell Surface - metabolism; Receptors, Endothelin; Swine; Wheat Germ Agglutinins
• ISSN: 0160-2446
• DOI: 10.1097/00005344-199100177-00039

Scintillation proximity assay (SPA) technology has been used to investigate the competitive binding of [125I]endothelin-1 (ET-1) by ET-1, endothelin-2 (ET-2), endothelin-3 (ET-3), sarafotoxin 6b (SFTX-b), and big endothelin (big ET) to endothelin receptors in human placenta and porcine lung. Specific binding of [125I]ET-1 to high-affinity receptors was detected in membranes coupled to wheat germ agglutinin (WGA)-coated beads impregnated with scintillant (fluomicrospheres). The binding characteristics of ET-1 were similar in both of the tissues studied. In contrast, the receptor-binding properties of ET-2, ET-3, and SFTX-b were different in human placental and porcine lung membranes. This suggests that different endothelin receptor populations exist in these tissues. In addition, the binding characteristics of ET-3 and SFTX-b differed markedly to those of ET-1 and ET-2 in both tissues. This may be due to the four amino acid residue substitution in the N-terminal loop of both ET-3 and SFTX-b. We have also demonstrated that the ET-1 precursor, big ET, competitively inhibits [125I]ET-1 binding in these tissues, but is 100-fold less potent than ET-1.