Sraer J, Baud L, Cosyns J P, Verroust P, Nivez M P, Ardaillou R
J Clin Invest. 1977 Jan;59(1):69-81. doi: 10.1172/JCI108623.
125I-angiotensin II (AII) specifically bound to rat glomerular basement membrane (GBM). The kinetics of binding were similar to those obtained with the total glomeruli. The apparent dissociation constant was close to 50 pM with both preparations. The number of sites related to the amount of protein was two times greater with GBM than with total glomeruli. Since the amount of GBM protein extracted from a given amount of glomerular protein was about 10%, it was possible to estimate the share of the GBM binding sites for AII as representing 20% of the total number present in the entire glomerulus. Binding studies at equilibrium as a function of 125I-AII concentration and competitive binding experiments suggested either multiplicity of the binding sites or cooperativity in the binding reaction. Degradation of 125I-AII in the presence of GBM was slight and did not increase with time. The difference in the degrees of degradation of 125I-AII was too small to account for the observed difference in binding when the results obtained with GBM and isolated glomeruli preparations were compared. 125I-AII binding to GBM was increased after treatment of these membranes with collagenase, slightly diminished with neuraminidase, and almost completely abolished with trypsin suggesting the proteic nature of the receptor. 125I-AII binding to GBM was diminished after incubation of GBM with anti-GBM antibodies as a result of a decrease in the number of binding sites. 125I-AII binding was even more diminished in preparations of glomeruli isolated from rats passively immunized with anti-GBM antibodies when compared with glomeruli from control animals. This resulted from both smaller affinity for AII and decrease in the number of the binding sites. The present data provides evidence for specific binding sites for AII localized on GBM. This is noteworthy since receptors for polypeptide hormones are currently observed on the surface of cell membranes. These findings also suggest a new physiological role for AII which might involve modification of GBM permeability.
125I-血管紧张素II（AII）特异性结合于大鼠肾小球基底膜（GBM）。其结合动力学与全肾小球所获结果相似。两种制剂的表观解离常数均接近50皮摩尔。与全肾小球相比，GBM中与蛋白量相关的结合位点数量多两倍。由于从给定数量的肾小球蛋白中提取的GBM蛋白量约为10%，因此有可能估计GBM上AII结合位点的份额占整个肾小球中总位点数量的20%。平衡时的结合研究作为125I-AII浓度的函数以及竞争性结合实验表明，结合位点具有多样性或结合反应中存在协同性。在GBM存在的情况下，125I-AII的降解轻微且不随时间增加。当比较GBM和分离的肾小球制剂所获结果时，125I-AII降解程度差异过小，无法解释观察到的结合差异。用胶原酶处理这些膜后，125I-AII与GBM的结合增加，用神经氨酸酶处理则略有减少，用胰蛋白酶处理几乎完全消除，这表明受体具有蛋白质性质。用抗GBM抗体孵育GBM后，由于结合位点数量减少，125I-AII与GBM的结合减少。与对照动物的肾小球相比，用抗GBM抗体被动免疫的大鼠分离的肾小球制剂中，125I-AII结合甚至减少得更多。这是由于对AII的亲和力降低以及结合位点数量减少所致。目前的数据为GBM上存在AII特异性结合位点提供了证据。这值得注意，因为目前在细胞膜表面观察到多肽激素受体。这些发现还提示了AII可能涉及GBM通透性改变的新生理作用。
