Quamme G, Pfeilschifter J, Murer H
Institute of Physiology, University of Zurich, Switzerland.
Biochim Biophys Acta. 1989 Sep 19;1013(2):159-65. doi: 10.1016/0167-4889(89)90044-x.
Parathyroid hormone (PTH) inhibits sodium/phosphate (Na+/Pi) cotransport across the apical membrane of opossum kidney (OK) cells principally through two pathways. First, cAMP stimulation and activation of protein kinase A; second, diacylglycerol release and stimulation of protein kinase C. Studies were designed to determine the importance of these regulatory cascades. Down-regulation of protein kinase C with prolonged phorbol ester (12-O-tetradecanoylphorbol 13-acetate (TPA] treatment leads to a refractory state in which the cells do not respond to PTH (10(-8) M), cAMP (10(-4) M) or rechallenge of TPA (200 nM) even though Na+/Pi cotransport is similar to control cells (8.1 +/- 0.1 nmol.mg-1 protein.5 min-1). Staurosporine, an inhibitor of protein kinase C, resulted in the complete inhibition of PTH, cAMP and TPA action in a dose-dependent manner. PTH, cAMP and TPA were additive below maximal concentrations, but had no further effect at maximal agonist concentrations. These results suggest that protein kinase C activity is important in PTH-mediated inhibition of Na+/phosphate cotransport in OK cells.
甲状旁腺激素（PTH）主要通过两条途径抑制负鼠肾（OK）细胞顶膜上的钠/磷酸盐（Na+/Pi）协同转运。第一，cAMP刺激并激活蛋白激酶A；第二，二酰基甘油释放并刺激蛋白激酶C。本研究旨在确定这些调节级联反应的重要性。用佛波酯（12-O-十四酰佛波醇13-乙酸酯（TPA））长期处理使蛋白激酶C下调，导致细胞进入不应期，在此期间细胞对PTH（10^(-8) M）、cAMP（10^(-4) M）或再次加入TPA（200 nM）均无反应，尽管Na+/Pi协同转运与对照细胞相似（8.1±0.1 nmol·mg^(-1)蛋白质·5 min^(-1)）。蛋白激酶C抑制剂星形孢菌素以剂量依赖方式完全抑制PTH、cAMP和TPA的作用。在最大浓度以下，PTH、cAMP和TPA的作用具有加和性，但在最大激动剂浓度时不再有进一步作用。这些结果表明，蛋白激酶C活性在PTH介导的OK细胞Na+/磷酸盐协同转运抑制中起重要作用。
