Study of glucose uptake in adipose cells.

Glucose is the main metabolic fuel in mammalian cells. Glucose entry into cells is facilitated by a family of ubiquitously expressed glucose transporter proteins. Typically, glucose transporters are localized on the plasma membrane. One notable exception is the glucose transporter isoform 4 (Glut4), which is specifically expressed in insulin sensitive tissues, i.e., skeletal muscle, heart muscle, and fat, and is responsible for the insulin effect on blood glucose clearance (1). Under basal conditions, Glut4 is compartmentalized in intracellular membrane vesicles and thus has no access to the extracellular space. Upon insulin administration, Glut4-containing vesicles fuse with the plasma membrane and deliver the transporter to its site of action. As a result, Glut4 content on the plasma membrane is increased, and glucose uptake in the cell is significantly elevated. Here, we describe two complementary techniques. The first one uses tritiated 2-deoxyglucose and is designed to measure insulin-stimulated glucose transport into cultured adipose cells. The second allows one to quantify the degree of Glut4 translocation from an intracellular compartment to the plasma membrane.