GLOSSARY

GLUT4 is the main glucose transporter in skeletal muscle, heart muscle and adipose tissue. Its key feature is that at rest it is mostly stored in intracellular vesicles and only moves to the cell membrane when it receives the right signal (translocation).

Two Activation Pathways

• Insulin pathway: insulin binds its receptor → IRS → PI3K → Akt → phosphorylation of AS160 (TBC1D4) → vesicles move to the membrane.
• Contraction pathway: muscle contraction sends vesicles to the membrane independently of insulin, through AMPK (the energy sensor), calcium and calmodulin, and the protein Rac1, acting via TBC1D1.

These two pathways are additive; that is why exercise and insulin together increase glucose uptake more than either alone.

Adaptation to Training

Endurance and resistance training