EFFECT OF IMMOBILIZATION ON GLUCOSE-TRANSPORT AND GLUCOSE-TRANSPORTER EXPRESSION IN RAT SKELETAL-MUSCLE

The effect of 42-48 h of immobilization by casting on maximal velocity of 3-O-methylglucose (3-MG) transport in skeletal muscle was studied in the perfused rat hindquarter. Immobilization resulted in a decrease of similar to 42% for maximum insulin-stimulated 3-MG transport in fast-twitch red fibers and a decrease of similar to 42% for contraction-stimulated transport in slow-twitch red fibers compared with nonimmobilized control muscle. No effect of immobilization on 3-MG transport was found in fast-twitch white muscle. Combination of insulin and muscle contractions always resulted in glucose transport that was identical in immobilized and control muscle. Western blot did not detect a decrease in GLUT-1 or GLUT-4 protein with immobilization. Furthermore, in fast-twitch red fibers, insulin receptor number and receptor kinase activity did not differ between immobilized and control muscle. It is concluded that during short-term immobilization a resistance of muscle glucose transport to stimulation develops that is fiber type specific and selective for insulin or contractions. The resistance can be overcome by the combined action of insulin and contractions and reflect factors other than glucose transporter number and insulin receptor binding and receptor kinase activity.