How does skeletal muscle contraction increase glucose uptake independently of insulin?

• A. Activation of cAMP-PKA Pathway
• B. Increased GLUT4 Transcription Without Translocation
• C. Activation of AMPK Leading to GLUT4 Translocation
• D. Inhibition of GLUT4 Endocytosis

Answer: (C)

When muscle cells contract, their energy demand rises and the cellular energy state shifts to a higher AMP/ADP level relative to ATP. This activates AMP-activated protein kinase (AMPK). Activated AMPK triggers the movement of GLUT4-containing vesicles to the muscle cell surface, increasing glucose transport into the cell without requiring insulin signaling. This rapid translocation provides the glucose needed for glycolysis to fuel ongoing contraction, explaining why glucose uptake can rise even in the absence of insulin.

Other options don’t explain the fast, contraction-driven uptake as well. The cAMP-PKA pathway isn’t the primary driver of GLUT4 translocation during exercise and is more tied to other metabolic effects like glycogen breakdown or lipolysis. Simply increasing GLUT4 transcription would take longer and wouldn’t account for the immediate uptake seen during activity. While reducing GLUT4 endocytosis could influence surface levels, the established acute mechanism that aligns with contraction is AMPK-mediated translocation of GLUT4 to the membrane.