Glucose Ingestion Causes GLUT4 Translocation in Human Skeletal Muscle

In humans, ingestion of carbohydrates causes an increase in blood glucose concentration, pancreatic insulin release, and increased glucose disposal into skeletal muscle. The underlying molecular mechanism for the increase in glucose disposal in human skeletal muscle after carbohydrate ingestion is not known. We determined whether glucose ingestion increases glucose uptake in human skeletal muscle by increasing the number of glucose transporter proteins at the cell surface and/or by increasing the activity of the glucose transporter proteins in the plasma membrane. Under local anesthesia, ∼1 g of vastus lateralis muscle was obtained from six healthy subjects before and 60 min after ingestion of a 75-g glucose load. Plasma membranes were isolated from the skeletal muscle and used to measure GLUT4 and GLUT1 content and glucose transport in plasma membrane vesicles. Glucose ingestion increased the plasma membrane content of GLUT4 per gram muscle (3,524 ± 729 vs. 4,473 ± 952 arbitrary units for basal and 60 min, respectively; P < 0.005). Transporter-mediated glucose transport into plasma membrane vesicles was also significantly increased (130 ± 11 vs. 224 ± 38 pmol · mg⁻¹ · s⁻¹; P < 0.017), whereas the calculated ratio of glucose transport to GLUT4, an indication of transporter functional activity, was not significantly increased 60 min after glucose ingestion (2.3 ± 0.4 vs. 3.0 ± 0.5 pmol · GLUT4 arbitrary units⁻¹ · s⁻¹; P < 0.17). These results demonstrate that oral ingestion of glucose increases the rate of glucose transport across the plasma membrane and causes GLUT4 translocation in human skeletal muscle. These findings suggest that under physiological conditions the translocation of GLUT4 is an important mechanism for the stimulation of glucose uptake in human skeletal muscle.