Insulin-induced translocation of facilitative glucose transporters in fetal/neonatal rat skeletal muscle

1 University of Pittsburgh School of Medicine, Magee-Womens Research Institute, Pittsburgh, Pennsylvania 15213-3180; and 2 Divisions of Neonatology and Developmental Biology, Department of Pediatrics, David Geffen School of Medicine at University of California-Los Angeles, Los Angeles, California 90095-1752 We examined the effect of insulin on fetal/neonatal rat skeletal muscle GLUT-1 and GLUT-4 concentrations and subcellular distribution by employing immunohistochemical analysis and subcellular fractionation followed by Western blot analysis. We observed that insulin did not alter total GLUT-1 or GLUT-4 concentrations or the GLUT-1 subcellular distribution in fetal/neonatal or adult skeletal muscle in 60 min. The basal and insulin-induced changes in subcellular distribution of GLUT-4 were different between the fetal/neonatal and adult skeletal muscle. Under basal conditions, sarcolemma-associated GLUT-4 was higher in the newborn compared with the adult, translating into a higher glucose transport. In contrast, insulin-induced translocation of GLUT-4 to the sarcolemma- and insulin-induced glucose transport was lower in the newborn compared with the adult. This age-related change results in enhanced basal glucose transport to fuel myocytic proliferation and differentiation while relatively curbing the insulin-dependent glucose transport in the newborn. development; glucose transport; subcellular localization * J. He and M. Thamotharan contributed equally to this work.