EFFECTS OF MUSCLE-ACTIVITY AND FIBER COMPOSITION ON GLUCOSE-TRANSPORTAND GLUT-4

We examined glucose uptake and GLUT-4 in rat muscles [soleus (Sol), pl antaris (PL), extensor digitorum longus (EDL), tibialis anterior, and the red and white gastrocnemius (WG)]. In the normally innervated perf used rat hindlimb muscles the proportion of oxidative fibers was highl y correlated with the muscle's insulin-stimulated 3-0-methyl-D-glucose (3-MG) uptake (R 2 = 0.78) and GLUT-4 content (r = 0.94). Insulin-sti mulated 3-MG uptake and GLUT-4 were also highly correlated ( R 2 = 0.9 96). In 3-day denervated muscles, insulin-stimulated 3-MG uptake was r educed in all six muscles (-41 to -14.6%, P < 0.05), and GLUT-4 conten t was also reduced (-87.5 to -34.9%), except in the WG and EDL (P > 0. 05). A very high correlation was observed between the decrements in GL UT-4 (%) and the decrements in 3-MG uptake (%; r = 0.99). The relative ly greater loss in muscle activity (%) due to denervation in the Sol c ompared with the PL coincided with the reductions (%) in GLUT-4 and 3- MG uptake. These studies demonstrate that glucose uptake and GLUT-4 ar e regulated by insulin-independent means, namely the oxidative capacit y of the muscle and the normal activity level of the muscle.