Chu Chih-Ying, Kao Ying-Shun, Fong Jim C
Institute of Biochemistry, School of Life Sciences, National Yang-Ming University, Taipei, Taiwan, Republic of China.
J Cell Biochem. 2002;85(1):83-91.
We used nigericin, a K+/H+ exchanger, to test whether glucose transport in 3T3-L1 adipocytes was modulated by changes in intracellular pH. Our results showed that nigericin increased basal but decreased insulin-stimulated glucose uptake in a time- and dose-dependent manner. Whereas the basal translocation of GLUT1 was enhanced, insulin-stimulated GLUT4 translocation was inhibited by nigericin. On the other hand, the total amount of neither transporter protein was altered. The finding that insulin-stimulated phosphoinositide 3-kinase (PI 3-kinase) activity was not affected by nigericin implies that nigericin exerted its inhibition at a step downstream of PI 3-kinase activation. At maximal dose, nigericin rapidly lowered cytosolic pH to 6.7; however, this effect was transient and cytosolic pH was back to normal in 20 min. Removal of nigericin from the incubation medium after 20 min abolished its enhancing effect on basal but had little influence on its inhibition of insulin-stimulated glucose transport. Moreover, lowering cytosolic pH to 6.7 with an exogenously added HCl solution had no effect on glucose transport. Taken together, it appears that nigericin may inhibit insulin-stimulated glucose transport mainly by interfering with GLUT4 translocation, probably by a mechanism not related to changes in cytosolic pH.
我们使用尼日利亚菌素（一种钾离子/氢离子交换剂）来测试3T3-L1脂肪细胞中的葡萄糖转运是否受细胞内pH值变化的调节。我们的结果表明，尼日利亚菌素以时间和剂量依赖性方式增加基础葡萄糖摄取，但降低胰岛素刺激的葡萄糖摄取。虽然GLUT1的基础转位增强，但尼日利亚菌素抑制胰岛素刺激的GLUT4转位。另一方面，两种转运蛋白的总量均未改变。胰岛素刺激的磷酸肌醇3-激酶（PI 3-激酶）活性不受尼日利亚菌素影响这一发现表明，尼日利亚菌素在PI 3-激酶激活的下游步骤发挥其抑制作用。在最大剂量下，尼日利亚菌素迅速将胞质pH值降至6.7；然而，这种作用是短暂的，胞质pH值在20分钟内恢复正常。20分钟后从孵育培养基中去除尼日利亚菌素消除了其对基础葡萄糖摄取的增强作用，但对其抑制胰岛素刺激的葡萄糖转运影响不大。此外，用外源添加的盐酸溶液将胞质pH值降至6.7对葡萄糖转运没有影响。综上所述，尼日利亚菌素可能主要通过干扰GLUT4转位来抑制胰岛素刺激的葡萄糖转运，其机制可能与胞质pH值变化无关。
