2-deoxyglucose transport and metabolism in caco-2 cells.
Bissonnette, Pierre, H[acute]el[grave]ene Gagn[acute]e, Anne Blais,
and Alfred Berteloot.
Membrane Transport Research Group, Department of Physiology,
Faculty of Medicine, University of Montreal, CP 6128, succursale
"Centre-Ville", Montr[acute]eal (Qu[acute]ebec) Canada H3C
3J7, Phone: (514) 343-5634, Fax: (514) 343-2111
APStracts 2:0148G, 1995.
We investigated the kinetics of 2-deoxyglucose (DG) uptake and
metabolism in Caco-2 cells since this human cell line may represent a
valid enterocyte model to assess the dynamics between sugar transport
and metabolism, and hence to get insights into the factors involved
during the intracellular phase of glucose absorption. When studied in
14-day-old monolayers, DG uptake is characterized by a lag phase with
a time course matching the decrease in intracellular glucose
concentrations, and no intracellular glucose-6-phosphate (G6P) can be
detected at any time during incubation. Following 1-h preincubation
of Caco-2 cells in substrate-free transport medium, however, steady
-state DG uptake matches deoxyglucose-6-phosphate (DG6P) accumulation
with undetectable levels of free DG. This complex behaviour in DG
uptake is linked to high hexokinase activity in Caco-2 cells, and the
enzyme has a Km value for glucose that is typical of hexokinase type
II (0.120 +/- 0.003 mM). Caco-2 cells also contain low level glucose
-6-phosphatase (G6Pase) activity that may account for the levelling
-off in DG uptake, and the kinetics of DG transport may be attributed
to the existence of a predominant pathway with a Km of 1.7 +/- 0.2
mM. Finally, analysis of the growth-related expression of DG
transport and hexokinase activity clearly shows that DG uptake is
lowest in post-confluent cells when hexokinase is at its highest
levels. We thus conclude that: i) transport is the rate-limiting step
during DG accumulation; ii) G6P is a potent inhibitor of hexokinase
activity as compared to DG6P, so that enzyme inhibition may have
physiological relevance in diverting glucose from metabolism during
its active reabsorption in the small intestine; iii) low levels of
G6Pase activity seem to exclude this enzyme and, hence, the
endoplasmic reticulum, as important factors during the intracellular
phase of glucose transport.
Received 28 July 1994; accepted in final form 10 July 1995.
APS Manuscript Number G282-4.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on 30 July 1995.