Characterization of angiotensin II binding sites in the human term placenta

• Published in: Molecular and cellular endocrinology Vol. 63; no. 1; pp. 111 - 119
• Main Authors: Tencé, Martine, Petit, Alain
• Format: Journal Article
• Language: English
• Published: Shannon Elsevier Ireland Ltd 01.05.1989; Elsevier
• Subjects: Adenylate cyclase; Adenylyl Cyclases - metabolism; Angiotensin II; Angiotensin II - analysis; Angiotensin II - metabolism; Binding Sites; Biological and medical sciences; Cell Membrane - metabolism; Cell Membrane - ultrastructure; Electrophoresis, Polyacrylamide Gel; Embryology: invertebrates and vertebrates. Teratology; Female; Fundamental and applied biological sciences. Psychology; General aspects. Development. Fetal membranes; Human placenta; Humans; Membrane receptor; Photoaffinity labeling; Placenta - cytology; Placenta - metabolism; Placenta - ultrastructure; Pregnancy; Human placenta; Adenylate cyclase; Membrane receptor; Photoaffinity labeling; Angiotensin II; Human; Radiolabelling; Fetal membrane; Gel electrophoresis; Enzyme; Peptide hormone; Photoaffinity labelling; Autoradiography; Competitive fixation; Placenta; Enzymatic activity; Woman; Hormonal receptor
• ISSN: 0303-7207; 1872-8057
• DOI: 10.1016/0303-7207(89)90087-7

Specific angiotensin II (AII) binding sites were identified and characterized in membranes from human term placenta. The binding of iodinated [ 125I](Sar 1)AII was time-dependent and saturable; it could be totally reversed on addition of unlabelled (Sar 1) AII and GTP + NaCl. Scatchard plot analysis of dose-dependent [ 125I](Sar 1)AII binding indicated the presence of a single class of binding sites with an equilibrium dissociation constant of 0.27 ± 0.06 nM and a maximum binding capacity of 38.4 ± 4.3 fmol/mg protein. The affinity of five AII analogues for the placental receptor was determined in competitive binding assays; the order of inhibitory potency was: (Sar 1)AII > (Sar 1, Ile 8)AII ~ (Sar 1, Ala 8)AII ~ AII > angiotensin I > (Des-Phe 8)AII. (Sar 1)AII did not cause any significant change in the basal or stimulated adenylate cyclase activity. In order to investigate the subunit molecular structure of the placenta AII receptor, membranes were covalently labelled with the photoaffinity ligand [ 125I](Sar 1, (4N 3Phe) 8)AII. Sodium dodecylsulfate-polyacrylamide gel electrophoresis followed by autoradiography showed that the labelling was specifically incorporated into a protein of M r 92000 in the presence or absence of dithiothreitol. It therefore appears that the All receptor from human placenta has the same binding and pharmacological properties as other well-known AH receptors; by contrast, it is characterized by a significantly higher molecular weight, pointing out that structural differences in All receptors may exist between species.