Translocation of the Glucose Transporter GLUT4 in Cardiac Myocytes of the Rat

• Published in: Proceedings of the National Academy of Sciences - PNAS Vol. 88; no. 17; pp. 7815 - 7819
• Main Authors: SLOT, J. W, GEUZE, H. J, GIGENGACK, S, JAMES, D. E, LIENHARD, G. E
• Format: Journal Article
• Language: English
• Published: Washington, DC National Academy of Sciences of the United States of America 01-09-1991; National Acad Sciences
• Subjects: Adipocytes; Albumins; Analytical, structural and metabolic biochemistry; Animals; Binding and carrier proteins; Biological and medical sciences; Brown adipocytes; Cell Membrane - metabolism; Cell membranes; Cells; exocytosis; Facilitative glucose transport proteins; Fundamental and applied biological sciences. Psychology; Glucose - pharmacology; Heart - drug effects; Insulin; Insulin - pharmacology; Male; Monosaccharide Transport Proteins - metabolism; Myocardium - cytology; Myocardium - metabolism; Physical Exertion; Proteins; Rats; Rats, Inbred Strains; Sarcolemma; White adipocytes; Heart; Rat; Immunocytochemistry; Biological transport; Diabetes mellitus; Rodentia; Glucose; Insulin; Myocyte; Vertebrata; Mammalia; Carbohydrate; Carrier protein
• ISSN: 0027-8424; 1091-6490
• DOI: 10.1073/pnas.88.17.7815

The insulin-regulated glucose transporter GLUT4 was immunolocalized in rat cardiac muscle under conditions of basal and stimulated glucose uptake, achieved by fasting and a combined exercise/insulin stimulus, respectively. In basal myocytes there was very little (<1%) GLUT4 in the different domains of the plasma membrane (sarcolemma, intercalated disk, and transverse tubular system). GLUT4 was localized in small tubulo-vesicular elements that occur predominantly near the sarcolemma and the transverse tubular system and in the trans-Golgi region. Upon stimulation ≈42% of GLUT4 was found in the plasma membrane. Each domain of the plasma membrane contributed equally to this effect. GLUT4-positive, clathrin-coated pits were also present at each cell surface domain. The remainder of the labeling was in tubulo-vesicular elements at the same sites as in basal cells and in the intercalated disk areas. The localization of GLUT4 in cardiac myocytes is essentially the same as in brown adipocytes, skeletal muscle, and white adipocytes. We conclude that increased glucose transport in muscle and fat is accounted for by translocation of GLUT4 from the intracellular tubulo-vesicular elements to the plasma membrane. The labeling of coated pits indicates that in stimulated myocytes, as in adipocytes, GLUT4 recycles constantly between the endosomal compartment and the plasma membrane and that stimulation of the exocytotic rate constant is likely the major mechanism for GLUT4 translocation.