Effects of activity level and type of muscle on glucose transporter protein concentration

In this study, we investigated the possibility that GLUT 4 protein concentration and mitochondrial enzyme activity is coregulated by muscle contractile activity. In the first experiment, male rats were trained by treadmill running or swimming for 3 wks and training effects in upper-and hind-limb muscle were investigated. Treadmill training program induced increases of 30% in citrate synthase activity, 51% in hexokinase activity, and 35% in GLUT 4 protein concentration in hind-limb soleus muscles without causing training effects in upperlimb epitrochlearis muscles. On the other hand, swimming training program induced increases of 67% in citrate synthase activity, 139% in hexokinase activity, and 89% in GLUT 4 protein concentration in epitrochlearis muscle without causing training effects in soleus muscles. These results suggest that muscle contractile activity which raises mitochondrial enzyme activity increases GLUT 4 protein concentration in skeletal muscle. In a second set of experiment, we investigated relationship between muscle GLUT 4 protein concentration and mitochondrial enzyme activity by use of the various type of rat muscles (soleus, plantaris, red gastrocnemius, white gastrocnemius, epitrochlearis and heart), which possese different contractile activity level. Significant correlation was observed between GLUT 4 protein concentration and citrate synthase activity among different muscles (r=0.936). They suggest that muscle GLUT 4 protein concentration and mitochondrial enzyme activity level may be coregulated according to muscle contractile activity level.