EVIDENCE AGAINST PROTEIN-KINASE-B AS A MEDIATOR OF CONTRACTION-INDUCED GLUCOSE-TRANSPORT AND GLUT4 TRANSLOCATION IN RAT SKELETAL-MUSCLE

Both insulin and muscle contraction stimulate glucose transport activi ty. However, contraction stimulation does not involve the insulin sign alling intermediate phosphatidylinositol 3-kinase (PI 3-kinase), Prote in kinase B (PKB) has recently been identified as a direct downstream target of PI 3-kinase in the insulin signalling pathway. We have exami ned here whether the two stimuli share PKB as a convergent step in sep arate signalling pathways. Insulin stimulates both glucose transport, GLUT4 cell-surface content and PKB activity (by 4-6-fold above basal) in a wortmannin-sensitive manner in in vitro incubated rat soleus musc les. By contrast, muscle contraction, which stimulates glucose transpo rt and the cell surface content of GLUT4 by 3-fold above basal levels, had no effect on PKB activity. These data demonstrate that PKB is not a mediator of contraction-induced glucose transport and GLUT4 translo cation. (C) 1998 Federation of European Biochemical Societies.