This comes to an uptake of 15–40 µmol/min/leg. At rest in an overnight fasted individual, leg glucose uptake is very low, reflected by the small femoral arterial minus femoral venous (A-V) glucose difference in the order of 0.05–0.1 mmol/L and the leg blood flow around 300–400 mL/min ( 5– 12). In humans, muscle glucose uptake during exercise is mostly measured across one or two legs or across the arm by measuring the arteriovenous difference of glucose (glucose extraction) multiplied by the blood flow in the leg or arm. GLUT4, glucose transporter type 4 G6P, glucose 6-phosphate. This includes plasma glucose concentration, capillary perfusion, transcapillary transport of glucose out of the capillary, transmembrane transport into the myocyte and phosphorylation, and further metabolism of glucose inside the myocyte. 1).įigure 1.Potential sites of regulation of muscle glucose uptake during exercise. These are as follows: 1) glucose supply (plasma glucose concentration and blood flow), 2) transcapillary transport out of the capillaries to the interstitium, 3) glucose transport across the sarcolemma and t-tubules, and 4) glucose phosphorylation and subsequent metabolism inside the muscle cell ( Fig. Nevertheless, in vivo muscle glucose uptake is dependent on four factors and three of them do not depend on GLUT4. Studies in GLUT4 knockout mice have convincingly shown that GLUT4 is necessary for contractions as well as insulin to increase muscle glucose uptake ( 1– 4). Glucose entry into skeletal muscle cells occurs by facilitated diffusion provided by glucose transporter type 4 (GLUT4) and a concentration gradient of glucose from the interstitial space (the outside of the muscle cell) to the inside (cytoplasm) of the muscle cell. Exercise markedly increases muscle glucose uptake.
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