Das S K, Mukherjee S, Banerjee D K
Department of Biochemistry, Meharry Medical College, Nashville, TN 37208.
Mol Cell Biochem. 1994 Nov 9;140(1):49-54. doi: 10.1007/BF00928365.
beta-Adrenoreceptor has been studied in a clonal capillary endothelial cell line established from the vascular bed of the bovine adrenal medulla. [3H]Dihydroalprenolol ([3H]DHA) binding to the isolated plasma membranes from these cells has demonstrated the presence of beta-adrenoreceptors with two different affinities. The dissociation constants (Kd) have been found to be 0.27 +/- 0.09 x 10(-9) M and 2.96 +/- 0.31 x 10(-9) M, respectively with the corresponding Bmax of 5.1 +/- 0.05 and 70.0 +/- 0.2 pmol/mg protein, respectively. Inhibition of [3H]DHA binding to the beta-receptor by atenolol (a beta 1-antagonist) and ICI 118,551 (a beta 2-antagonist) has suggested that the IC50cor (= Ki) for atenolol and ICI 118,551 for high affinity site are 0.08 +/- 0.03 x 10(-12) M and 0.25 +/- 0.08 x 10(-12) M, respectively. This, therefore, indicates that both atenolol and ICI 118,551 are able to displace the bound ligand effectively but the beta 1-selective antagonist atenolol is 3 times more potent than its beta 2 counterpart, ICI 118,551. Displacement of [3H]DHA binding to the endothelial cell plasma membrane by the agonists isoproterenol, epinephrine and norepinephrine has established a relative order of Ki for these agents as isoproterenol (0.56 +/- 0.19 x 10(-9) M) < epinephrine (0.77 +/- 0.26(-9) M) > or = norepinephrine (0.71 +/- 0.24 x 10(-9) M) for the high affinity site. The corresponding values for the low affinity site, however, are 4.62 +/- 0.64 x 10(-9) M, 6.21 +/- 0.86 x 10(-9) M and 5.90 +/- 0.82 x 10(-9) M, respectively for the same agonists. Increased intracellular cAMP accompanied with cellular proliferation in the presence of isoproterenol has suggested not only the coupling of beta-adrenoreceptors to the adenylate cyclase system but also its involvement in endothelial cell proliferation.
已在源自牛肾上腺髓质血管床的克隆性毛细血管内皮细胞系中对β-肾上腺素能受体进行了研究。[3H]二氢心得舒（[3H]DHA）与这些细胞分离的质膜结合，已证明存在具有两种不同亲和力的β-肾上腺素能受体。已发现解离常数（Kd）分别为0.27±0.09×10⁻⁹ M和2.96±0.31×10⁻⁹ M，相应的最大结合容量（Bmax）分别为5.1±0.05和70.0±0.2 pmol/mg蛋白质。阿替洛尔（一种β1拮抗剂）和ICI 118,551（一种β2拮抗剂）对[3H]DHA与β受体结合的抑制作用表明，阿替洛尔和ICI 118,551对高亲和力位点的半数抑制浓度（IC50cor = Ki）分别为0.08±0.03×10⁻¹² M和0.25±0.08×10⁻¹² M。因此，这表明阿替洛尔和ICI 118,551均能有效取代结合的配体，但β1选择性拮抗剂阿替洛尔的效力比其β2对应物ICI 118,551强3倍。激动剂异丙肾上腺素、肾上腺素和去甲肾上腺素对[3H]DHA与内皮细胞质膜结合的取代作用，确定了这些药物对高亲和力位点的Ki相对顺序为异丙肾上腺素（0.56±0.19×10⁻⁹ M）＜肾上腺素（0.77±0.26×10⁻⁹ M）≥去甲肾上腺素（0.71±0.24×10⁻⁹ M）。然而，对于低亲和力位点，相同激动剂的相应值分别为4.62±0.64×10⁻⁹ M、6.21±0.86×10⁻⁹ M和5.90±0.82×10⁻⁹ M。在异丙肾上腺素存在下，细胞内cAMP增加并伴有细胞增殖，这不仅表明β-肾上腺素能受体与腺苷酸环化酶系统偶联，还表明其参与内皮细胞增殖。
