Regional difference in muscle fiber type and glucose uptake of mouse gastrocnemius at rest

Regional differences in muscle fiber types and their glucose uptake in superficial, middle and deep regions of mouse gastrocnemius at rest were studied. The enzyme activities of succinate dehydrogenase (SDH), alpha-glycerophosphate dehydrogenase (alpha-GPDH) and myofibrillar ATPase were used for the classification of each muscle fiber type. For the evaluations of glucose uptake, 2-deoxyglucose (2-DG) microradioautography and expression of the glucose transporter 4 (GLUT4) protein were applied. In superficial region of mouse gastrocnemius, all fibers were IIx or IIb and were low for 2-DG uptake and GLUT4 expression. They were anaerobic and fast twitch. In middle region, fibers showing low 2-DG uptake and small amounts of GLUT-4 protein (IIx and IIb) dominated (80.4%). Most fibers were anaerobic and fast twitch. Others were type IIc and IIa. In deep region, most fibers (86.9%) showed high 2-DG uptake and large amounts of GLUT4 protein (I, IIc and IIa). They were oxidative and slow twitch.