title: Immunolocalization of GLUT-1 glucose transporter in rat skeletal muscle and in normal and hypoxic cardiac tissue.
abstract: We compared the expression and cell-type localization of GLUT-1 mRNA and protein between cardiac and skeletal muscle of normal rats. Also, since we recently showed that cardiac GLUT-1 is upregulated in rats exposed to hypobaric hypoxia, we examined the cellular localization of GLUT-1 in cardiac tissue of normal and hypoxic rats. Confocal light microscopy and double immunofluorescent labeling revealed intense localization of GLUT-1 around neurofilament immunoreactivity within gastrocnemius muscle consistent with the previously described localization of large amounts of GLUT-1 in perineurial sheaths of skeletal muscle. However, using the same methods, we were unable to visualize GLUT-1 adjacent to nerve fibers in numerous sections of right or left ventricles or atria. Compared with skeletal myoctes, however, GLUT-1 immunofluorescence among cardiomyocytes was much more intense, particularly along the plasma membrane and especially intercalated discs. GLUT-1 immunofluorescence was also seen within the walls of arterioles within the heart. The predominant localization of GLUT-1 expression to cardiomyocytes in heart tissue was confirmed by in situ mRNA hybridization to digoxigenin-conjugated GLUT-1 cDNA. Northern blot analysis demonstrated that GLUT-1 mRNA was increased severalfold in the cardiac tissues compared with skeletal muscle. Although we detected GLUT-1 protein by immunoblotting of detergent extracts of the heart, we could not detect GLUT-1 in similar extracts of skeletal muscle. The cell type distribution of GLUT-1 in hearts of hypoxic rats was not different by immunohistochemistry from normals. These data indicate that 1) the cell-type distribution of GLUT-1 in the heart differs markedly from that in skeletal muscle. GLUT-1 in cardiac tissue, unlike skeletal muscle, is predominantly expressed within myocytes. 2) Cardiac GLUT-1 is not located along nerve fibers. 3) GLUT-1 mRNA and protein levels in cardiac tissue are considerably greater than in skeletal muscle. 4) The hypoxia-induced increase in cardiac GLUT-1 that we previously reported must occur within cardiomyocytes.
authors.affiliation: Department of Internal Medicine, Veterans Affairs Medical Center, Iowa City, Iowa.
authors.forename: C L
authors.initials: CL
authors.lastname: Doria-Medina
authors.forename: D D
authors.initials: DD
authors.lastname: Lund
authors.forename: A
authors.initials: A
authors.lastname: Pasley
authors.forename: A
authors.initials: A
authors.lastname: Sandra
authors.forename: W I
authors.initials: WI
authors.lastname: Sivitz
mesh_terms: D000818:Animals; D051272:Glucose Transporter Type 1; D000860:Hypoxia / Q000378:metabolism*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000235:genetics / Q000378:metabolism*; D009132:Muscles / Q000378:metabolism*; D009206:Myocardium / Q000378:metabolism*; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012016:Reference Values
chemical_list: D051272:Glucose Transporter Type 1; D009004:Monosaccharide Transport Proteins; D012333:RNA, Messenger; C495679:Slc2a1 protein, rat