GLUT4 ready to go

Vesicles containing the glucose transporter GLUT4 travel rapidly on a microtubule network that lies just under the plasma membrane in resting cells, according to results from Lizunov et al. (page 481). The vesicles occasionally touch the plasma membrane and, when stimulated by insulin, quickly fuse with it.

GLUT4 is sequestered in vesicles in resting cells. Insulin exposure induces the vesicles to fuse to the plasma membrane. But how these vesicles are stored in the resting cell was unclear.

To find out, the team used total internal reflection fluorescence (TIRF) microscopy on freshly isolated adipose cells transfected with GLUT4-GFP. Whereas confocal microscopy illuminated vesicles scattered throughout the cytoplasm, TIRF movies showed the vesicles just under the plasma membrane. These sub-membrane vesicles were moving on microtubules in unstimulated cells. Within ten minutes of insulin exposure,...