title: Insulin-induced recruitment of glucose transporter 4 (GLUT4) and GLUT1 in isolated rat cardiac myocytes. Evidence of the existence of different intracellular GLUT4 vesicle populations.
abstract: Using isolated rat cardiomyocytes we have examined: 1) the effect of insulin on the cellular distribution of glucose transporter 4 (GLUT4) and GLUT1, 2) the total amount of these transporters, and 3) the co-localization of GLUT4, GLUT1, and secretory carrier membrane proteins (SCAMPs) in intracellular membranes. Insulin induced 5.7- and 2.7-fold increases in GLUT4 and GLUT1 at the cell surface, respectively, as determined by the nonpermeant photoaffinity label [3H]2-N-[4(1-azi-2,2,2-trifluoroethyl)benzoyl]-1, 3-bis-(D-mannos-4-yloxy)propyl-2-amine. The total amount of GLUT1, as determined by quantitative Western blot analysis of cell homogenates, was found to represent a substantial fraction ( approximately 30%) of the total glucose transporter content. Intracellular GLUT4-containing vesicles were immunoisolated from low density microsomes by using monoclonal anti-GLUT4 (1F8) or anti-SCAMP antibodies (3F8) coupled to either agarose or acrylamide. With these different immunoisolation conditions two GLUT4 membrane pools were found in nonstimulated cells: one pool with a high proportion of GLUT4 and a low content in GLUT1 and SCAMP 39 (pool 1) and a second GLUT4 pool with a high content of GLUT1 and SCAMP 39 (pool 2). The existence of pool 1 was confirmed by immunotitration of intracellular GLUT4 membranes with 1F8-acrylamide. Acute insulin treatment caused the depletion of GLUT4 in both pools and of GLUT1 and SCAMP 39 in pool 2.
  
  
  CONCLUSIONS
  1) GLUT4 is the major glucose transporter to be recruited to the surface of cardiomyocytes in response to insulin; 2) these cells express a high level of GLUT1; and 3) intracellular GLUT4-containing vesicles consist of at least two populations, which is compatible with recently proposed models of GLUT4 trafficking in adipocytes.
authors.affiliation: Institute of Physiology, Medical Faculty, RWTH Aachen, Pauwelsstrasse 30, Aachen D-52057, Federal Republic of Germany.
authors.forename: Y
authors.initials: Y
authors.lastname: Fischer
authors.forename: J
authors.initials: J
authors.lastname: Thomas
authors.forename: L
authors.initials: L
authors.lastname: Sevilla
authors.forename: P
authors.initials: P
authors.lastname: Muñoz
authors.forename: C
authors.initials: C
authors.lastname: Becker
authors.forename: G
authors.initials: G
authors.lastname: Holman
authors.forename: I J
authors.initials: IJ
authors.lastname: Kozka
authors.forename: M
authors.initials: M
authors.lastname: Palacín
authors.forename: X
authors.initials: X
authors.lastname: Testar
authors.forename: H
authors.initials: H
authors.lastname: Kammermeier
authors.forename: A
authors.initials: A
authors.lastname: Zorzano
mesh_terms: D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002478:Cells, Cultured; D003594:Cytoplasmic Granules / Q000378:metabolism; D005260:Female; D005947:Glucose / Q000378:metabolism; D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D009206:Myocardium / Q000378:metabolism* / Q000648:ultrastructure; D051381:Rats; D017207:Rats, Sprague-Dawley
chemical_list: D051272:Glucose Transporter Type 1; D051275:Glucose Transporter Type 4; D007004:Hypoglycemic Agents; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495679:Slc2a1 protein, rat; C495694:Slc2a4 protein, rat; D005947:Glucose