Assays of Glucose Entry, Glucose Transporter Amount, and Translocation

Glucose enters the cell by a carrier-mediated, facilitated diffusion mechanism, which, in most tissues, exhibits no energy or counter-ion requirements. In adipose tissues and skeletal muscle, glucose entry is acutely regulated by insulin and other hormones (1 ,2 ). Indeed, in those tissues, glucose transporter 4 (GLUT4) is the chief isoform which is, in basal conditions, retained in a specific intracellular storage compartment (3 ). The GLUT4-containing vesicles are translocated to the plasma membrane in response to insulin, thus allowing for the massive entry of glucose into the cells (1 ,2 ). Adipocytes also contain a small proportion of the ubiquituously expressed glucose transporter, GLUT1, which is at a similar level at the plasma membranes and inside the cell (3 ). Because of this basal distribution, insulin effect on GLUT1 translocation is minor.