Glucose transporter expression in human skeletal muscle fibers

The present study was initiated to investigate GLUT-1 through -5 expression in developing and mature human skeletal muscle. To bypass the problems inh erent in techniques using tissue homogenates, we applied an immunocytochemi cal approach, employing the sensitive enhanced tyramide signal amplificatio n (TSA) technique to detect the localization of glucose transporter express ion in human skeletal muscle. We found expression of GLUT-1, GLUT-3, and GL UT-4 in developing human muscle fibers showing a distinct expression patter n. 1) GLUT-1 is expressed in human skeletal muscle cells during gestation, but its expression is markedly reduced around birth and is further reduced to undetectable levels within the first year of life; 2) GLUT-3 protein exp ression appears at 18 wk of gestation and disappears after birth; and 3) GL UT-4 protein is diffusely expressed in muscle cells throughout gestation, w hereas after birth, the characteristic subcellular localization is as seen in adult muscle fibers. Our results show that GLUT-1, GLUT-3, and GLUT-4 se em to be of importance during muscle fiber growth and development. GLUT-5 p rotein was undetectable in fetal and adult skeletal muscle fibers. In adult muscle fibers, only GLUT-4 was expressed at significant levels. GLUT-1 imm unoreactivity was below the detection limit in muscle fibers, indicating th at this glucose transporter is of minor importance for muscle glucose suppl y. Thus we hypothesize that GLUT-4 also mediates basal glucose transport in muscle fibers, possibly through constant exposure to tonal contraction and basal insulin levels.