Intestinal glucose transport: evidence for a membrane traffic-based pathway in humans.
OBJECTIVE
The presence of glucose transporter 2 (GLUT2) molecules in the basolateral membrane of enterocytes has long been considered to be of major importance for intestinal glucose absorption. The aim of this study was to reevaluate the role of GLUT2 in a patient with congenital GLUT2 deficiency (Fanconi-Bickel syndrome, FBS).


METHODS
Oral mono- and disaccharide tolerance tests including gaschromatographic determination of breath hydrogen concentrations were performed in an FBS patient. For comparison, a patient with a microsomal carbohydrate transport defect, glucose-6-phosphate translocase 1 (G6PT1) deficiency, and a control individual were investigated.


RESULTS
No increase in breath hydrogen concentration was found in the GLUT2-deficient patient after a glucose load. In G6PT1 deficiency, basal hydrogen concentrations were repeatedly found to be elevated.


CONCLUSIONS
From the fact that a GLUT2-deficient patient does not show any impairment of intestinal monosaccharide transport measurable by the hydrogen breath test, we conclude that mechanisms other than facilitative glucose transport by GLUT2 must be involved in the transport of monosaccharides at the basolateral membrane of enterocytes. When relating this observation to the high intestinal expression of human hexokinase, G6PT1, and glucose-6-phosphatase and to our results of oral carbohydrate tolerance tests in a G6PT1-deficient patient, there is evidence that a microsomal membrane traffic-based transport pathway, as recently suggested for GLUT2-deficient animals, also plays a major role in transcellular monosaccharide transport of the human intestine.
Santer
René
R
University Children's Hospital, Schwanenweg 20, D-24105 Kiel, Germany. santer@pediatrics.uni-kiel.de
Hillebrand
Georg
G
Steinmann
Beat
B
Schaub
Jürgen
J
D000328:Adult; D017920:Antiporters / Q000172:deficiency; D001944:Breath Tests; D002648:Child; D005260:Female; D005947:Glucose / Q000494:pharmacology; D051273:Glucose Transporter Type 2; D006801:Humans; D006859:Hydrogen; D007413:Intestinal Mucosa / Q000378:metabolism*; D008297:Male; D008566:Membranes / Q000378:metabolism; D008661:Metabolism, Inborn Errors / Q000378:metabolism; D009004:Monosaccharide Transport Proteins / Q000172:deficiency* / Q000378:metabolism*; D009994:Osmolar Concentration; D012119:Respiration
D017920:Antiporters; D051273:Glucose Transporter Type 2; D009004:Monosaccharide Transport Proteins; C503531:SLC37A4 protein, human; C111261:glucose 6-phosphate(transporter); D006859:Hydrogen; D005947:Glucose