Burns K D, Harris R C
Department of Medicine, University of Ottawa, Ontario, Canada.
Am J Physiol. 1995 Apr;268(4 Pt 1):C925-35. doi: 10.1152/ajpcell.1995.268.4.C925.
Angiotensin II (ANG II) receptors of the AT1 subtype are present on the apical and basolateral membranes of renal proximal tubule cells. Cells of the proximal tubulelike cell line, LLC-PK1/Cl4, were transfected with an expression plasmid containing cDNA encoding the rabbit AT1 ANG II receptor. In transfected cells, specific binding of 125I-ANG II was detected on both apical and basolateral membranes; wild-type LLC-PK1/Cl4 cells did not express ANG II receptors. In transfected cells, apical or basolateral ANG II increased both S6 kinase activity and incorporation of [3H]leucine. In cells pretreated with pertussis toxin, the stimulatory effect of apical or basolateral ANG II on [3H]leucine incorporation was abolished. In contrast, ANG II did not affect mitogenesis, determined by [3H]thymidine incorporation. Apical or basolateral ANG II (10(-6) M) stimulated phosphoinositide turnover by 13.4 +/- 4.4% (n = 8) and 16.3 +/- 4.2% (n = 9), respectively. The activity of protein kinase C, determined by phosphorylation of a specific protein kinase C peptide substrate, was also stimulated by ANG II in transfected cells. Apical or basolateral ANG II had no significant effect on cellular adenosine 3',5'-cyclic monophosphate levels. In permeabilized transfected cells, apical ANG II (10(-6) M) inhibited the phosphorylation of a specific peptide substrate of protein kinase A; lower apical concentrations or basolateral ANG II were without significant effect. These results indicate that AT1 ANG II receptors sort to both apical and basolateral membranes in renal epithelial cells and are coupled to activation of phospholipase C. ANG II stimulates protein synthesis by binding to either apical or basolateral receptors; this effect requires coupling to G proteins and may be mediated by activation of S6 kinase. Because high concentrations of ANG II exist in proximal tubule, binding to apical and basolateral receptors may regulate proximal tubule cell growth under physiological conditions.
1型血管紧张素II（ANG II）受体存在于肾近端小管细胞的顶端膜和基底外侧膜上。用含有编码兔1型ANG II受体cDNA的表达质粒转染近端小管样细胞系LLC-PK1/Cl4细胞。在转染细胞中，在顶端膜和基底外侧膜上均检测到125I-ANG II的特异性结合；野生型LLC-PK1/Cl4细胞不表达ANG II受体。在转染细胞中，顶端或基底外侧的ANG II均可增加S6激酶活性以及[3H]亮氨酸的掺入。在用百日咳毒素预处理的细胞中，顶端或基底外侧ANG II对[3H]亮氨酸掺入的刺激作用被消除。相反，ANG II不影响通过[3H]胸苷掺入测定的细胞增殖。顶端或基底外侧的ANG II（10^(-6) M）分别刺激磷酸肌醇周转率13.4±4.4%（n = 8）和16.3±4.2%（n = 9）。通过特异性蛋白激酶C肽底物的磷酸化测定的蛋白激酶C活性在转染细胞中也受到ANG II的刺激。顶端或基底外侧的ANG II对细胞3',5'-环磷酸腺苷水平无显著影响。在透化的转染细胞中，顶端的ANG II（10^(-6) M）抑制蛋白激酶A特异性肽底物的磷酸化；较低的顶端浓度或基底外侧的ANG II无显著影响。这些结果表明，1型ANG II受体在肾上皮细胞中定位于顶端膜和基底外侧膜，并与磷脂酶C的激活偶联。ANG II通过与顶端或基底外侧受体结合来刺激蛋白质合成；这种作用需要与G蛋白偶联，并且可能由S6激酶的激活介导。由于近端小管中存在高浓度的ANG II，与顶端和基底外侧受体结合可能在生理条件下调节近端小管细胞的生长。
