PHOSPHATIDYLINOSITOL 3-KINASE AND THE ACTIN NETWORK ARE NOT REQUIRED FOR THE STIMULATION OF GLUCOSE-TRANSPORT CAUSED BY MITOCHONDRIAL UNCOUPLING - COMPARISON WITH INSULIN ACTION

In L6 myotubes insulin stimulates glucose transport through the transl ocation of glucose transporters GLUT1, GLUT3 and GLUT4 from intracellu lar stores to the plasma membrane. An intact actin network and phospha tidylinositol 3-kinase activity are required for this process. Glucose transport is also stimulated by the mitochondrial ATP-production unco upler dinitrophenol. We show there that, in serum-depleted myotubes, d initrophenol induced translocation of GLUT1 and GLUT4, but not GLUT3. This response was not affected by inhibiting phosphatidylinositol 3-ki nase or disassembling the actin network. Insulin, but not dinitropheno l, caused tyrosine phosphorylation of several polypeptides, including the insulin-receptor substrate-1 and mitogen-activated protein kinase. Similarly, insulin, but not dinitrophenol, caused actin reorganizatio n, which was inhibited by wortmannin. We conclude that insulin and din itrophenol stimulate glucose transport by different mechanisms.