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This Article Full Text Full Text (PDF) All Versions of this Article: 287/2/E348    most recent 00538.2003v1 Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via ISI Web of Science (7) Citing Articles via Google Scholar Google Scholar Articles by Capilla, E. Articles by Planas, J. V. Search for Related Content PubMed PubMed Citation Articles by Capilla, E. Articles by Planas, J. V.

Functional characterization of an insulin-responsive glucose transporter (GLUT4) from fish adipose tissue

¹Departament de Fisiologia, Facultat de Biologia, Universitat de Barcelona, 08028 Barcelona, Spain; ²Department of Pharmacology, The State University of New York, Stony Brook, New York 11794; ³Institut für Pharmakologie, Freie Universität Berlin, 14195 Berlin, Germany

Submitted 26 November 2003 ; accepted in final form 21 April 2004

Glucose transport across the plasma membrane is mediated by a family of glucose transporter proteins (GLUTs), several of which have been identified in mammalian, avian, and, more recently, in fish species. Here, we report on the cloning of a salmon GLUT from adipose tissue with a high sequence homology to mammalian GLUT4 that has been named okGLUT4. Kinetic analysis of glucose transport following expression in Xenopus laevis oocytes demonstrated a 7.6 ± 1.4 mM K_m for 2-deoxyglucose (2-DG) transport measured under zero-trans conditions and 14.4 ± 1.5 mM by equilibrium exchange of 3-O-methylglucose. Transport of 2-DG by okGLUT4-injected oocytes was stereospecific and was competed by D-glucose, D-mannose, and, to a lesser extent, D-galactose and D-fructose. In addition, 2-DG uptake was inhibited by cytochalasin B and ethylidene glucose. Moreover, insulin stimulated glucose uptake in Xenopus oocytes expressing okGLUT4 and in isolated trout adipocytes, which contain the native form of okGLUT4. Despite differences in protein motifs important for insulin-stimulated translocation of mammalian GLUT4, okGLUT4 was able to translocate to the plasma membrane from intracellular localization sites in response to insulin when expressed in 3T3-L1 adipocytes. These data demonstrate that okGLUT4 is a structural and functional fish homolog of mammalian GLUT4 but with a lower affinity for glucose, which could in part explain the lower ability of fish to clear a glucose load.

glucose uptake; Xenopus oocytes; immunolocalization

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