Fructose transport and GLUT-5 protein in human sarcolemmal vesicles.

“The exercise-induced translocation of glucose transporters is due to an increase in the plasma membrane content of the GLUT-4 isoform, because a single bout of exercise does not alter the abundance of plasma membrane GLUT-1 (23, 36, 38) or GLUT-5 (66).”

“GLUT5 SLC2A5 Human muscle [90,91] C2C12 [71] Mouse muscle [92] L6 myotubes [93] Rat muscle [94]”

“The facilitative fructose transporter, GLUT5, is expressed in but not limited to tissues which are insulin sensitive in both humans and rodents (Shepherd et al. 1992, Kristiansen et al. 1997, Darakhshan et al. 1998, Hajduch et al. 1998) where it transports dietary fructose into cells.”

“However, mammalian studies reveal that dietary fructose is converted to glucose by the liver (Delarue et al., 1993); blood fructose concentration is low and skeletal muscles display low capacities for fructose oxidation (Kristiansen et al., 1997; Kristiansen et al., 1996).”

“In rat skeletal muscles, maximal rates of fructose transport are approximately eightfold lower than rates of glucose transport (Kristiansen et al., 1997).”

“This raises the possibility that these animals, which receive ,50% of their calories in the form of fructose [57,58], may be capable of transporting this hexose directly from circulation into their muscle cells and oxidizing it at rates much higher than maximal capacities seen in most mammals [59,60].”

“This con rasts with the skeletal muscles of rats and hum ns that t ansport and metabolize fructose at much lower rates than gluco [65,66] and, as not d previously, their more limited capacity to directly fuel exercise metabolism with dietary glucose and fructose [67].”

“In contrast, fructose is primarily absorbed by the protein carrier, GLUT-5 (SLC2A5), which is not Na+ dependent [34, 41].”

“In human muscle preparations ex vivo, fructose was readily taken up and metabolized to lactate in a dose-responsive manner [51], and in human skeletal muscle sarcolemmal vesicles (which express GLUT5), fructose uptake occurred but at a lower rate than glucose and via a distinct pathway [52,53].”

“For the ingestion of fructose GLUT-5 is of major importance [1] [2] [3] [4] [5] [6].”

“The higher concentration of glucose in the blood and the greater abundance of membrane glucose transporters than fructose transporters, in combination, result in the preferential uptake and extrahepatic metabolism of glucose (Zierath et al., 1995; Kristiansen et al., 1997).”

“Skeletal muscles possess lower capacities for fructose transport (Kristiansen et al. 1997) and oxidation (Zierath et al. 1995) relative to glucose.”

“Der GLUT5, der in der Muskulatur des Schweins nur sehr schwer nachzuweisen war, wurde als passiver D-Fruktose-Transporter in der Skelettmuskulatur des Menschen bereits beschrieben (KRISTIANSEN et al. 1997).”