EFFECT OF IMMOBILIZATION ON GLUCOSE-TRANSPORT AND GLUCOSE-TRANSPORTEREXPRESSION 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 fa st-twitch red fibers and a decrease of similar to 42% for contraction- stimulated transport in slow-twitch red fibers compared with nonimmobi lized control muscle. No effect of immobilization on 3-MG transport wa s 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 decre ase in GLUT-1 or GLUT-4 protein with immobilization. Furthermore, in f ast-twitch red fibers, insulin receptor number and receptor kinase act ivity did not differ between immobilized and control muscle. It is con cluded that during short-term immobilization a resistance of muscle gl ucose transport to stimulation develops that is fiber type specific an d selective for insulin or contractions. The resistance can be overcom e by the combined action of insulin and contractions and reflect facto rs other than glucose transporter number and insulin receptor binding and receptor kinase activity.