del Carmen Caro M, Montiel M, Jiménez E
Departmento de Bioquímica y Biología Molecular, Facultad de Medicina, Universidad de Málaga, Spain.
Life Sci. 1998;62(1):51-7. doi: 10.1016/s0024-3205(97)01037-0.
In rat liver plasma membrane a single angiotensin II (Ang II) binding site (Kd of 3.71 +/- 0.33 nM and Bmax of 1143.7 +/- 83.9 fmol/mg protein) was identified using radioligand binding assay. Pharmacologically, this receptor match with the AT1 receptor subtypes in term of affinity for the selective antagonist Losartan, and probably with the AT1A receptor form in term of insensitivity for the antagonist PD123319. Nevertheless, using polyacrylamide gel isoelectric focusing, two 125I-Ang II binding sites migrating to pI 6.8 and 6.5 were found in these membrane preparations. Monophasic displacement of 125I-Ang II bound to isoform migrating at pI 6.8 clearly indicate that this isoform represents a functional Ang II-receptor complex. In contrast, the high concentrations of agonist and peptidic derivates of Ang necessary to displace 125I-Ang II bound to isoform migrating at pI 6.5 indicate that this atypical 125I-Ang II binding site represents a biologically nonfunctional Ang II binding molecule, presumably a nonspecific 125I-Ang II binding site.
利用放射性配体结合试验，在大鼠肝细胞膜中鉴定出一个单一的血管紧张素II（Ang II）结合位点（解离常数Kd为3.71±0.33 nM，最大结合容量Bmax为1143.7±83.9 fmol/mg蛋白质）。从药理学角度来看，就对选择性拮抗剂氯沙坦的亲和力而言，该受体与AT1受体亚型匹配；而就对拮抗剂PD123319不敏感而言，可能与AT1A受体形式匹配。然而，使用聚丙烯酰胺凝胶等电聚焦法，在这些膜制剂中发现了两个迁移至等电点6.8和6.5的125I-Ang II结合位点。与迁移至等电点6.8的异构体结合的125I-Ang II的单相置换清楚地表明，该异构体代表一种功能性Ang II受体复合物。相反，要置换与迁移至等电点6.5的异构体结合的125I-Ang II，需要高浓度的Ang激动剂和肽衍生物，这表明这个非典型的125I-Ang II结合位点代表一种生物学上无功能的Ang II结合分子，大概是一个非特异性125I-Ang II结合位点。
