de Godoy Márcio A F, Rattan Satish
Jefferson Medical College of Thomas Jefferson University, Department of Medicine, Philadelphia, PA 19107, USA.
J Pharmacol Exp Ther. 2006 Dec;319(3):1088-95. doi: 10.1124/jpet.106.108084. Epub 2006 Sep 19.
Previous studies have reported bimodal effects by angiotensin II (Ang II) in the rat internal anal sphincter (IAS), a concentration-dependent contraction (at lower concentrations) and relaxation (at higher concentrations). The experiments suggest the above-mentioned responses are the result of Ang II subtype I receptor(s) (AT(1)-R) and subtype II receptor(s) (AT(2)-R) activation, respectively. These studies determined the role and mechanism of AT(2)-R-induced relaxation of the smooth muscle cells (SMCs) from the IAS in response to Ang II. Laser confocal microscopy showed that in the basal state, the AT(1)-Rs reside in the plasma membrane, whereas AT(2)-Rs are present in the cytosol. Higher concentrations of Ang II caused movement of AT(1)-R and AT(2)-R in opposite directions to the cytosol and the membrane, respectively. Losartan (AT(1)-R antagonist) but not S-(+)-1-([4-(dimethylamino)-3-methylphenyl]methyl)-5-(diphenylacetyl)-4,5,6,7-tetrahydro-1H-imidazo(4,5-c)pyridine-6-carboxylic acid (PD123319; AT(2)-R antagonist) selectively inhibited these movements. These results are based on biotinylation assays, confocal images, and Western blot analyses of the densities of AT(1)-Rs and AT(2)-Rs in the plasma membrane versus cytosolic fractions of the IAS SMCs. Ang II in higher concentrations did not change the total contents of Ang II receptors. These data combined with the functional data using measurements of IAS SMC lengths suggest that internalization of AT(1)-R and externalization of AT(2)-R may be responsible for the activation of the AT(2)-R, which leads to the relaxation of the IAS with higher concentrations of Ang II.
先前的研究报道了血管紧张素II（Ang II）对大鼠内括约肌（IAS）的双峰效应，即浓度依赖性收缩（较低浓度时）和舒张（较高浓度时）。实验表明，上述反应分别是Ang II I型受体（AT(1)-R）和II型受体（AT(2)-R）激活的结果。这些研究确定了AT(2)-R诱导IAS平滑肌细胞（SMC）舒张以响应Ang II的作用和机制。激光共聚焦显微镜显示，在基础状态下，AT(1)-R位于质膜，而AT(2)-R存在于细胞质中。较高浓度的Ang II导致AT(1)-R和AT(2)-R分别向细胞质和质膜的相反方向移动。氯沙坦（AT(1)-R拮抗剂）而非S-(+)-1-([4-(二甲基氨基)-3-甲基苯基]甲基)-5-(二苯乙酰基)-4,5,6,7-四氢-1H-咪唑并(4,5-c)吡啶-6-羧酸（PD123319；AT(2)-R拮抗剂）选择性抑制这些移动。这些结果基于生物素化测定、共聚焦图像以及对IAS SMC质膜与细胞质部分中AT(1)-R和AT(2)-R密度的蛋白质印迹分析。较高浓度的Ang II并未改变Ang II受体的总含量。这些数据与使用IAS SMC长度测量的功能数据相结合表明，AT(1)-R的内化和AT(2)-R的外化可能是AT(2)-R激活的原因，这导致较高浓度的Ang II使IAS舒张。
