Use of quantitative immunofluorescence microscopy to study intracellular trafficking: studies of the GLUT4 glucose transporter.

Insulin regulates the glucose uptake in muscle and adipose cells by acutely modulating the amount of the GLUT4 glucose transporter in the plasma membrane. The steady-state cell surface distribution of a membrane protein is an equilibrium between exocytosis and endocytosis. The authors study the effect of insulin on GLUT4 using quantitative immunofluorescence microscopy adapted to single-cell analysis. They use an HA-GLUT4-GFP reporter molecule as a surrogate of GLUT4 trafficking. Insulin induces an increase of GLUT4 in the plasma membrane by both increasing GLUT4 exocytosis and decreasing its endocytosis. Quantitative immunofluorescence techniques such as those described in this review can be used to study the trafficking of virtually any membrane protein.