Which glucose transporter is translocated to the cell surface in response to insulin in muscle and adipose tissue?

• A. GLUT4
• B. GLUT1
• C. GLUT2
• D. SGLT1

Answer: (A)

Insulin boosts glucose uptake in muscle and fat by moving a specific glucose transporter to the cell surface. This transporter, GLUT4, sits inside vesicles when insulin isn’t active; after insulin binds its receptor, a signaling cascade (involving IRS proteins, PI3K, and Akt) triggers these GLUT4-containing vesicles to fuse with the plasma membrane. Once on the surface, GLUT4 facilitates glucose entry into the cell, helping to lower blood glucose quickly after meals.

Other transporters don’t behave the same way. GLUT1 provides constitutive glucose uptake in many tissues and isn’t mobilized by insulin. GLUT2 is found in liver, kidney, and pancreatic beta cells and is not insulin-dependent translocation. SGLT1 is a sodium-glucose cotransporter in the intestinal lining (and certain renal reabsorption sites) that uses active transport with sodium, not a regulated insertion into the membrane by insulin.