AJP - Heart Calcium Transients and Cell-Sarcomere
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Am J Physiol Heart Circ Physiol 292: H2009-H2019, 2007. First published December 22, 2006; doi:10.1152/ajpheart.00663.2006 Free Article
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Immunogold labeling study of the distribution of GLUT-1 and GLUT-4 in cardiac tissue following stimulation by insulin or ischemia

Katherine A. B. Davey,1 Pamela B. Garlick,1 Alice Warley,2 and Richard Southworth1

1Division of Imaging Sciences and 2Centre for Ultrastructural Imaging, Guy's, King's, and St. Thomas' School of Medicine, King's College London, London, United Kingdom

Submitted 22 June 2006 ; accepted in final form 11 December 2006

Whereas glucose transporter 1 (GLUT-1) is thought to be responsible for basal glucose uptake in cardiac myocytes, little is known about its relative distribution between the different plasma membranes and cell types in the heart. GLUT-4 translocates to the myocyte surface to increase glucose uptake in response to a number of stimuli. The mechanisms underlying ischemia- and insulin-mediated GLUT-4 translocation are known to be different, raising the possibility that the intracellular destinations of GLUT-4 following these stimuli also differ. Using immunogold labeling, we describe the cellular localization of these two transporters and investigate whether insulin and ischemia induce differential translocation of GLUT-4 to different cardiac membranes. Immunogold labeling of GLUT-1 and GLUT-4 was performed on left ventricular sections from isolated hearts following 30 min of either insulin, ischemia, or control perfusion. In control tissue, GLUT-1 was predominantly (76%) localized in the capillary endothelial cells, with only 24% of total cardiac GLUT-1 present in myocytes. GLUT-4 was found predominantly in myocytes, distributed between sarcolemmal and T tubule membranes (1.84 ± 0.49 and 1.54 ± 0.33 golds/µm, respectively) and intracellular vesicles (127 ± 18 golds/µm2). Insulin increased T tubule membrane GLUT-4 content (2.8 ± 0.4 golds/µm, P < 0.05) but had less effect on sarcolemmal GLUT-4 (1.72 ± 0.53 golds/µm). Ischemia induced greater GLUT-4 translocation to both membrane types (4.25 ± 0.84 and 4.01 ± 0.27 golds/µm, respectively P < 0.05). The localization of GLUT-1 suggests a significant role in transporting glucose across the capillary wall before myocyte uptake via GLUT-1 and GLUT-4. We demonstrate independent spatial translocation of GLUT-4 under insulin or ischemic stimulation and propose independent roles for T-tubular and sarcolemmal GLUT-4.

glucose transporter; immunogold electron microscopy


Address for reprint requests and other correspondence: R. Southworth, The NMR Laboratory, Division of Imaging Sciences, 5th Floor Thomas Guy House, Guy's Hospital, St. Thomas' St., London, SE1 9RT, UK (e-mail: richard.southworth{at}kcl.ac.uk)






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