Becker B N, Harris R C
Department of Medicine, Vanderbilt University School of Medicine, Nashville, Tennessee, USA.
Kidney Int Suppl. 1996 Dec;57:S66-72.
Angiotensin II (Ang II) receptors in the proximal nephron significantly affect renal salt and water reabsorption. The predominant tubular-epithelial cell Ang II receptor, type 1 Ang II receptors (AT1R), is a member of the superfamily of G-protein-coupled receptors. Tubular cell AT1R are unusual as they are polarized to apical (AP) and basolateral (BL) cell membranes. In a proximal tubule cell model that mimics the in vivo polar distribution of AT1R (LLC-PKC14 cells transfected with rabbit AT1R), we have determined that AP and BL AT1R display differential rates of endocytosis and recycling. In addition, AP AT1R recycling was selectively inhibited by quinacrine, a non-specific inhibitor of phospholipase A2 (PLA2) activity and HELSS, a mechanism-based inhibitor of calcium-independent PLA2 activity. PLA2 catalyzes the hydroysis of sn-2 fatty acyl bonds, liberating free fatty acids and lysophosphoslipids, and proximal tubule AT1R are known to couple to PLA2 as a signaling pathway. In this model, AP Ang II treatment selectively stimulated [3H]-arachidonic acid ([3H]-AA) release. Furthermore, inhibiting AP AT1R endocytosis+recycling with either phenylarsine oxide (PAO) or HELSS, decreased AP Ang II-stimulated [3H]-AA release. In other studies, Ang II internalization also has been linked to vectorial sodium (Na+) flux. Preliminary studies in our model also suggested that HELSS inhibited AP Ang II-stimulated Na+ flux (AP --> BL), raising the possibility that AP AT1R targeting in proximal tubular epithelium, the endocytic profile of these receptors, and AP AT1R-mediated arachidonic acid release combine to serve as additional contributors to Ang II-mediated Na+ flux in the nephron.
近端肾单位中的血管紧张素II（Ang II）受体显著影响肾脏对盐和水的重吸收。主要的肾小管上皮细胞Ang II受体，即1型Ang II受体（AT1R），是G蛋白偶联受体超家族的成员。肾小管细胞AT1R不同寻常，因为它们在顶端（AP）和基底外侧（BL）细胞膜上呈极化分布。在一个模拟AT1R体内极性分布的近端小管细胞模型（转染了兔AT1R的LLC-PKC14细胞）中，我们已经确定AP和BL的AT1R表现出不同的内吞和再循环速率。此外，AP AT1R的再循环被喹吖因（一种磷脂酶A2（PLA2）活性的非特异性抑制剂）和HELSS（一种基于机制的钙非依赖性PLA2活性抑制剂）选择性抑制。PLA2催化sn-2脂肪酰键的水解，释放游离脂肪酸和溶血磷脂，并且已知近端小管AT1R作为一种信号通路与PLA2偶联。在这个模型中，AP Ang II处理选择性地刺激了[3H]-花生四烯酸（[3H]-AA）的释放。此外，用氧化苯胂（PAO）或HELSS抑制AP AT1R的内吞+再循环，降低了AP Ang II刺激的[3H]-AA释放。在其他研究中，Ang II的内化也与向量性钠（Na+）通量有关。我们模型中的初步研究还表明，HELSS抑制了AP Ang II刺激的Na+通量（AP→BL），这增加了一种可能性，即近端肾小管上皮细胞中AP AT1R的靶向、这些受体的内吞特征以及AP AT1R介导的花生四烯酸释放共同作为肾单位中Ang II介导的Na+通量的额外促成因素。
