Linder A Elizabeth, Thakali Keshari M, Thompson Janice M, Watts Stephanie W, Webb R Clinton, Leite Romulo
Department of Pharmacology and Toxicology, Michigan State University, B-445 Life Sciences Building, East Lansing, MI 48824-1317, USA.
J Pharmacol Exp Ther. 2007 Oct;323(1):78-84. doi: 10.1124/jpet.107.123463. Epub 2007 Jul 16.
Tachyphylaxis or desensitization is frequently observed following angiotensin II type I (AT1) receptor activation by angiotensin II. One of the possible mechanisms contributing to receptor desensitization involves receptor internalization. In addition to clathrin-coated pits/vesicles, caveolae, small invaginations in the plasma membrane rich in cholesterol, may also be involved in receptor internalization. After activation, AT1 receptor partially redistributes to lipid-enriched domains. We hypothesize that AT1 receptor internalization via caveolae contributes to the tachyphylactic response observed to angiotensin II. Endothelium-denuded rat aortic rings were exposed to increasing concentrations of angiotensin II or phenylephrine, generating two cumulative concentration-effect curves (CCEC) with a 90-min interval separating each curve (CCEC-I and CCEC-II). CCEC-II was performed in the presence of either vehicle or methyl-beta-cyclodextrin (CD), a drug that depletes cholesterol from the membrane and disassembles caveolae. CCEC-II to angiotensin II, but not to phenylephrine, was blunted in aortic rings treated with vehicle. In the presence of CD, CCEC-II did not differ significantly from CCEC-I for both agonists. CCEC-I to angiotensin II was abolished when in the presence of the AT1 receptor antagonist. The presence of AT1 receptors at the aortic smooth muscle cells' membrane treated with angiotensin II was observed by immunofluorescence only in the presence of CD. In addition, caveolin-1 coimmunoprecipitated with AT1 receptor after agonist stimulation, and this interaction was inhibited by CD. Our data suggest that caveolae are involved in the tachyphylactic contractile response induced by angiotensin II in rat aorta, and this effect is related to receptor internalization.
血管紧张素 II 激活血管紧张素 II 1 型（AT1）受体后，常出现快速耐受性或脱敏现象。导致受体脱敏的一种可能机制涉及受体内化。除了网格蛋白包被的小窝/囊泡外，质膜中富含胆固醇的小凹（小的内陷）也可能参与受体内化。激活后，AT1 受体部分重新分布到富含脂质的结构域。我们假设通过小凹的 AT1 受体内化促成了对血管紧张素 II 观察到的快速耐受性反应。将去内皮的大鼠主动脉环暴露于浓度递增的血管紧张素 II 或去氧肾上腺素中，生成两条累积浓度 - 效应曲线（CCEC），每条曲线间隔 90 分钟（CCEC - I 和 CCEC - II）。CCEC - II 在溶剂或甲基 - β - 环糊精（CD）存在的情况下进行，CD 是一种从膜中耗尽胆固醇并拆散小凹的药物。用溶剂处理的主动脉环中，对血管紧张素 II 的 CCEC - II 变钝，但对去氧肾上腺素的 CCEC - II 没有变钝。在 CD 存在的情况下，两种激动剂的 CCEC - II 与 CCEC - I 相比均无显著差异。当存在 AT1 受体拮抗剂时，对血管紧张素 II 的 CCEC - I 被消除。仅在 CD 存在的情况下，通过免疫荧光观察到用血管紧张素 II 处理的主动脉平滑肌细胞膜上存在 AT1 受体。此外，激动剂刺激后，小窝蛋白 - 1 与 AT1 受体共免疫沉淀，且这种相互作用被 CD 抑制。我们的数据表明，小凹参与了血管紧张素 II 在大鼠主动脉中诱导的快速耐受性收缩反应，且这种效应与受体内化有关。
