Direct evidence of fiber type-dependent GLUT-4 expression in human skeletal muscle

Departments of Pathology and of Endocrinology, Odense University Hospital, DK-5000 Odense; and Department of Physiology, Panum Institute, University of Copenhagen, DK-2200 Copenhagen, Denmark GLUT-4 expression in individual fibers of human skeletal muscles in younger and older adults was studied. Furthermore, the dependency of insulin-stimulated glucose uptake on fiber type distribution was investigated. Fiber type distribution was determined in cryosections of muscle biopsies from 8 younger (29 yr) and 8 older (64 yr) healthy subjects, and estimates of GLUT-4 expression in individual fibers were obtained by combining immunohistochemistry and stereology. GLUT-4 was more abundantly expressed in slow compared with fast muscle fibers in both younger ( P