Microautoradiographic studies of glucose uptake in skeletal muscle fibers at rest

In the present study, differences in glucose uptake by muscle fibers in deep, middle, and superficial regions of the gastrocnemius were studied at rest by 2-deoxyglucose (2-DG) microautoradiography. Expression of the glucose transporter 4 (GLUT-4) protein, an isoform of the glucose transporter family, was analyzed as well. These data were compared with the activity of succinate dehydrogenase, a marker of oxidative metabolism, a-glycerophosphate dehydrogenase, an indicator of the glycolytic capacity, and myofibrillar ATPase. In the deep regions of the muscle, most fibers (86.9%) showed high 2-DG uptake and large amounts of GLUT-4 protein, whereas in the superficial regions, all fibers showed low 2-DG uptake and GLUT-4 expression. In the middle regions, fibers dominated (80.4%) showed low 2-DG uptake and small amounts of GLUT-4 protein. Analysis of metabolic properties revealed that most fibers in the deep region were oxidative and showed the highest 2-DG uptake; in the superficial region, the fibers were anaerobic and showed the lowest 2-DG uptake. In the middle region, most fibers were of the anaerobic and fast twitch type. It is concluded that 2-DG uptake correlates with GLUT-4 expression in the plasma membrane of type I and IIx fibers rather than with oxidative enzyme activity.