Glucose transporter 3 (GLUT3) protein is present in human myocardium

Glucose and fructose enter mammalian cells via facilitated diffusion, a process regulated by five glucose transporter isoforms (GLUT1-5) at the plasma membrane. The tissue-specific pattern of GLUT isoform expression likely reflects differing needs for glucose transport by various tissues. Myocytes must respond expeditiously to increased metabolic demand. A basal isoform, GLUT1, and the insulin-regulatable glucose transporter, GLUT4, have been demonstrated in human myocytes. GLUT3 has a high affinity for glucose, but its presence in human myocardium has not been clearly established. The purpose of this study was to determine whether GLUT3 protein is present in human cardiac myocytes. We examined rapidly frozen myocardial tissue from the explanted heart of seven patients undergoing cardiac transplantation, from the heart of a young, previously healthy male organ donor, from the heart of a 67-year-old woman without known cardiac disease who had a fatal stroke, and from the heart of six human fetuses. GLUT3 protein was detected by immunoblots and localized by light and electron microscopy immunohistochemistry. The presence of GLUT3 protein was verified in myocardial tissue by both immunoblots and immunohistochemistry. Light and electron microscopy confirmed that GLUT3 was in cardiac myocytes. GLUT3 was also demonstrated as a 48 kDa protein in fetal myocardium, which was present at 10 weeks, increased at 15 weeks, then decreased at 20 weeks of gestation. GLUT3 is present in human adult and fetal myocardium. Human myocardial GLUT3 regulation and its role in myocardial glucose uptake remain to be elucidated.