Glucose transporters in the regulation of intestinal, renal and
liver glucose fluxes.
Thorens, Bernard.
Institute of Pharmacology and Toxicology, University of Lausanne,
27, Bugnon
APStracts 3:0022G, 1996.
Five functional mammalian facilitated hexose carriers (GLUTs) have
been characterized by molecular cloning. By functional expression in
heterologous systems, their specificity and affinity for different
hexoses have been defined. There are three high affinity (GLUT1,
GLUT3 and GLUT4) and one low affinity (GLUT2) transporters and GLUT5
is primarily a fructose carrier. Because their Michaelis constant is
below the normal blood glucose concentration, the high affinity
transporters function at rates close to Vmax. Thus, their level of
cell surface expression greatly influences the rate of glucose uptake
into the cells. In contrast, the rate of glucose uptake by GLUT2 (Km
= 17 mM) increases in parallel with the rise in blood glucose over
the physiological concentration range. High affinity transporters are
found in almost every tissues but their expression is higher in cells
with high glycolytic activity. GLUT2, however, is found in tissues
carrying large glucose fluxes such as intestine, kidney and liver. As
an adaptive response to variations in metabolic conditions the
expression of these transporters is regulated by glucose and
different hormones. Thus, because of their specific characteristics
and regulated expression, the facilitated glucose transporters
control fundamental aspects of glucose homeostasis. Here, I will
review data pertaining to the structure and regulated expression of
the glucose carriers present in intestine, kidney and liver and
discuss their role in the control of glucose fluxes into or out of
these different tissues.
Received 1 January 1996; accepted in final form 5 January 1996.
APS Manuscript Number G9-6.
Article publication pending Am. J. Physiol. (Gastrointest. Liver
Physiology).
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 29 January 96