Get 20M+ Full-Text Papers For Less Than $1.50/day. Start a 14-Day Trial for You or Your Team.

Learn More →

ATP-dependent sugar transport complexity in human erythrocytes

ATP-dependent sugar transport complexity in human erythrocytes Human erythrocyte glucose sugar transport was examined in resealed red cell ghosts under equilibrium exchange conditions (sugar intracellular = sugar extracellular , where brackets indicate concentration). Exchange 3- O -methylglucose (3MG) import and export are monophasic in the absence of cytoplasmic ATP but are biphasic when ATP is present. Biphasic exchange is observed as the rapid filling of a large compartment (66% cell volume) followed by the slow filling of the remaining cytoplasmic space. Biphasic exchange at 20 mM 3MG eliminates the possibility that the rapid exchange phase represents ATP-dependent 3MG binding to the glucose transport protein (GLUT1; cellular GLUT1 of ≤20 µM). Immunofluorescence-activated cell sorting analysis shows that biphasic exchange does not result from heterogeneity in cell size or GLUT1 content. Nucleoside transporter-mediated uridine exchange proceeds as rapidly as 3MG exchange but is monoexponential regardless of cytoplasmic ATP. This eliminates cellular heterogeneity or an ATP-dependent, nonspecific intracellular diffusion barrier as causes of biphasic exchange. Red cell ghost 3MG and uridine equilibrium volumes (130 fl) are unaffected by ATP. GLUT1 intrinsic activity is unchanged during rapid and slow phases of 3MG exchange. Two models for biphasic sugar transport are presented in which 3MG must overcome a sugar-specific, physical (diffusional), or chemical (isomerization) barrier to equilibrate with cell water. Partial transport inhibition with the use of cytochalasin B or maltose depresses both rapid and slow phases of transport, thereby eliminating the physical barrier hypothesis. We propose that biphasic 3MG transport results from ATP-dependent, differential transport of 3MG anomers in which V max /apparent K m for -3MG exchange transport is 19-fold greater than V max /apparent K m for α-3MG transport. carrier-mediated transport; transport kinetics; transport regulation Address for reprint requests and other correspondence: A. Carruthers, Dept. of Biochemistry and Molecular Pharmacology, Univ. of Massachusetts Medical School, 364 Plantation St., Worcester, MA 01605 (e-mail: anthony.carruthers@umassmed.edu ) http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png AJP - Cell Physiology The American Physiological Society

ATP-dependent sugar transport complexity in human erythrocytes

AJP - Cell Physiology , Volume 292 (2): C974 – Feb 1, 2007

Loading next page...
 
/lp/the-american-physiological-society/atp-dependent-sugar-transport-complexity-in-human-erythrocytes-ktXzrrgXM8

References (82)

Publisher
The American Physiological Society
Copyright
Copyright © 2010 the American Physiological Society
ISSN
0363-6143
eISSN
1522-1563
DOI
10.1152/ajpcell.00335.2006
pmid
16928769
Publisher site
See Article on Publisher Site

Abstract

Human erythrocyte glucose sugar transport was examined in resealed red cell ghosts under equilibrium exchange conditions (sugar intracellular = sugar extracellular , where brackets indicate concentration). Exchange 3- O -methylglucose (3MG) import and export are monophasic in the absence of cytoplasmic ATP but are biphasic when ATP is present. Biphasic exchange is observed as the rapid filling of a large compartment (66% cell volume) followed by the slow filling of the remaining cytoplasmic space. Biphasic exchange at 20 mM 3MG eliminates the possibility that the rapid exchange phase represents ATP-dependent 3MG binding to the glucose transport protein (GLUT1; cellular GLUT1 of ≤20 µM). Immunofluorescence-activated cell sorting analysis shows that biphasic exchange does not result from heterogeneity in cell size or GLUT1 content. Nucleoside transporter-mediated uridine exchange proceeds as rapidly as 3MG exchange but is monoexponential regardless of cytoplasmic ATP. This eliminates cellular heterogeneity or an ATP-dependent, nonspecific intracellular diffusion barrier as causes of biphasic exchange. Red cell ghost 3MG and uridine equilibrium volumes (130 fl) are unaffected by ATP. GLUT1 intrinsic activity is unchanged during rapid and slow phases of 3MG exchange. Two models for biphasic sugar transport are presented in which 3MG must overcome a sugar-specific, physical (diffusional), or chemical (isomerization) barrier to equilibrate with cell water. Partial transport inhibition with the use of cytochalasin B or maltose depresses both rapid and slow phases of transport, thereby eliminating the physical barrier hypothesis. We propose that biphasic 3MG transport results from ATP-dependent, differential transport of 3MG anomers in which V max /apparent K m for -3MG exchange transport is 19-fold greater than V max /apparent K m for α-3MG transport. carrier-mediated transport; transport kinetics; transport regulation Address for reprint requests and other correspondence: A. Carruthers, Dept. of Biochemistry and Molecular Pharmacology, Univ. of Massachusetts Medical School, 364 Plantation St., Worcester, MA 01605 (e-mail: anthony.carruthers@umassmed.edu )

Journal

AJP - Cell PhysiologyThe American Physiological Society

Published: Feb 1, 2007

There are no references for this article.