Fructose transport and glut5 protein in human sarcolemmal vesicles.. Kristiansen, S_ren, Froogh Darakhshan, Erik A. Richter, and Harinder S. Hundal. Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, 13 Universitetsparken, DK-2100, Copenhagen, Denmark, Department of Anatomy and Physiology, University of Dundee, Dundee, Scotland, U.K.
APStracts 4:0119E, 1997.
Sarcolemmal vesicles were produced from human skeletal muscle biopsy material obtained at rest and immediately after maximal (100% VO2 max) dynamic exercise for analysis of fructose transport and hexose transporter (GLUT5) protein concentration. Human sarcolemmal vesicles displayed a time dependent uptake of of D-fructose which displayed saturable Michaelis-Menten type kinetics (Vmax: 477 +/- 37 pmol min-1 mg-1 protein, Km : 8.3 +/- 1.2 mM). At a hexose concentration of 5 mM vesicle transport rate was 8 times faster for glucose than for fructose. Preincubation of human muscle vesicles with 35 [mu]M cytochalasin B prior to the uptake assay resulted in over 95 % inhibition in D-glucose uptake, whereas transport of D-fructose was unaffected. Sarcolemmal vesicles prepared from exercised human muscle showed a significant increase (49%) in vesicle GLUT4 content (p<0.03, n=10) which accounts for the increase in vesicle glucose transport which we have recently reported (Kristiansen et al., Am. J. Physiol, 270: E197-E201, 1996). In contrast exercise did not increase the vesicle GLUT5 protein content or induce changes in vesicle fructose transport activity. In conclusion, we propose that fructose transport into human skeletal muscle occurs via a mechanism distinct from that utilized by glucose based on differences in sensitivity to cytochalasin B and responsiveness to exercise. Furthermore, our findings signify that uptake of fructose in human skeletal muscle is mediated by the GLUT5 transporter. 

Received 1997 January 17; accepted in final form 1997 May 21
APS Manuscript Number E0028-7.
Article publication pending Am. J. Physiol. (Endocrinol. Metab.).
ISSN 1080-4757 Copyright 1997 The American Physiological Society.
Published in APStracts on 11 June 1997