ABSTRACT
Insulin stimulation was robust with a 6-fold increase in activity relative to basal values. This stimulation rate was also fairly constant over the course of the experiment. Despite the loss of insulin-sensitive glucose transport in glucose-deprived cells, the level of GLUT4 in the plasma membrane after exposure to insulin appears similar to glucose-fed cells. Raising glucose concentrations decreased transport activity in a protein synthesis-independent manner. Glucose deprivation increased the basal activity and over time reduced the ability of insulin to further stimulate. In 3T3-L1 adipocytes and other insulin-sensitive cells, GLUT4 expression must be considered in addition to GLUT1 in order to understand the effects of glucose deprivation. Removal of glucose from the medium results in a time-dependent loss of glycogen. Interestingly, there appears to be little difference in the level of GLUT4 in the low-density membrane fraction fraction in glucose-deprived cells relative to the fed controls.
