Scintillation proximity assay: competitive binding studies with [125I]endothelin-1 in human placenta and porcine lung.
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.
Berry
J A
JA
Cardiff Laboratories, Amersham International plc, U.K.
Burgess
A J
AJ
Towers
P
P
D000818:Animals; D001667:Binding, Competitive; D016232:Endothelins / Q000378:metabolism*; D005260:Female; D006801:Humans; D007457:Iodine Radioisotopes; D008168:Lung / Q000378:metabolism*; D008863:Microspheres; D010920:Placenta / Q000378:metabolism*; D011247:Pregnancy; D011956:Receptors, Cell Surface / Q000378:metabolism*; D017466:Receptors, Endothelin; D013552:Swine; D014909:Wheat Germ Agglutinins
D016232:Endothelins; D007457:Iodine Radioisotopes; D011956:Receptors, Cell Surface; D017466:Receptors, Endothelin; D014909:Wheat Germ Agglutinins