Fructose transport and GLUT-5 protein in human sarcolemmal vesicles.
Sarcolemmal vesicles were produced from human skeletal muscle biopsy material obtained at rest and immediately after maximal dynamic exercise (100% maximal O2 uptake) for analysis of fructose transport and hexose transporter (GLUT-5) protein concentration. Human sarcolemmal vesicles displayed a time-dependent uptake of D-fructose that displayed saturable Michaelis-Menten type kinetics (maximal transport 477 +/- 37 pmol.min-1.mg protein-1; half-maximal concentration constant 8.3 +/- 1.2 mM). At a hexose concentration of 5 mM, vesicle transport rate was eight times faster for glucose than for fructose. Preincubation of human muscle vesicles with 35 microM cytochalasin B before the uptake assay resulted in > 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 GLUT-4 content (P < 0.03, n = 10), which accounts for the increase in vesicle glucose transport that we have recently reported [S. Kristiansen, M. Hargreaves, and E.A. Richter. Am. J. Physiol. 270 (Endocrinol. Metab. 33): E197-E201, 1996]. In contrast, exercise did not increase the vesicle GLUT-5 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 on the basis of 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 GLUT-5 transporter.
Kristiansen
S
S
Copenhagen Muscle Research Centre, August Krogh Institute, University of Copenhagen, Denmark.
Darakhshan
F
F
Richter
E A
EA
Hundal
H S
HS
D000328:Adult; D001692:Biological Transport; D001706:Biopsy; D015444:Exercise; D005632:Fructose / Q000378:metabolism*; D005947:Glucose / Q000378:metabolism*; D051275:Glucose Transporter Type 4; D051296:Glucose Transporter Type 5; D006801:Humans; D007700:Kinetics; D008297:Male; D009004:Monosaccharide Transport Proteins / Q000378:metabolism*; D009124:Muscle Proteins; D018482:Muscle, Skeletal / Q000166:cytology / Q000502:physiology*; D005082:Physical Exertion / Q000502:physiology*; D012016:Reference Values; D012508:Sarcolemma / Q000378:metabolism*
D051275:Glucose Transporter Type 4; D051296:Glucose Transporter Type 5; D009004:Monosaccharide Transport Proteins; D009124:Muscle Proteins; C495692:SLC2A4 protein, human; D005632:Fructose; D005947:Glucose