Microautoradiographic studies of glucose uptake in skeletal muscle fibers at rest

In the present study, differences in glucose uptake by muscle fibers in dee p, middle, and superficial regions of the gastrocnemius were studied at res t by 2-deoxyglucose (2-DG) microautoradiography. Expression of the glucose transporter 4 (GLUT-4) protein, an isoform of the glucose transporter famil y, was analyzed as well. These data were compared with the activity of succ inate dehydrogenase, a marker of oxidative metabolism, a-glycerophosphate d ehydrogenase, an indicator of the glycolytic capacity, and myofibrillar ATP ase. In the deep regions of the muscle, most fibers (86.9%) showed high 2-D G uptake and large amounts of GLUT-4 protein, whereas in the superficial re gions, all fibers showed low 2-DG uptake and GLUT-4 expression. In the midd le regions, fibers dominated (80.4%) showed low 2-DG uptake and small amoun ts of GLUT-4 protein. Analysis of metabolic properties revealed that most f ibers 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 f ast twitch type. It is concluded that 2-DG uptake correlates with GLUT-4 ex pression in the plasma membrane of type I and IIx fibers rather than with o xidative enzyme activity.