Insulin affects glucose uptake in muscle and adipose tissue by which mechanism?

• A. It promotes translocation of GLUT4 transporters to the cell surface, increasing glucose uptake and utilization.
• B. It inhibits GLUT4 translocation.
• C. It changes GLUT2 expression.
• D. It reduces glucose uptake.

Answer: (A)

Insulin increases glucose uptake in muscle and adipose tissue by driving GLUT4 transporters to the cell surface. In these tissues, GLUT4 sits in intracellular vesicles when insulin levels are low. When insulin binds its receptor, a signaling cascade (involving IRS, PI3K, and AKT) triggers the vesicles to fuse with the plasma membrane, inserting more GLUT4 transporters. With more GLUT4 on the surface, glucose can enter the cells more readily, elevating uptake to match the post-meal needs and support storage as glycogen or fat. GLUT2 is not the transporter regulated in this acute uptake process in these tissues, and inhibiting GLUT4 translocation or reducing uptake would not reflect the insulin action described.