Glucose transporters: structure, function, and regulation.
Glucose is transported into the cell by facilitated diffusion via a family of structurally related proteins, whose expression is tissue-specific. One of these transporters, GLUT4, is expressed specifically in insulin-sensitive tissues. A possible change in the synthesis and/or in the amount of GLUT4 has therefore been studied in situations associated with an increase or a decrease in the effect of insulin on glucose transport. Chronic hyperinsulinemia in rats produces a hyper-response of white adipose tissue to insulin and resistance in skeletal muscle. The hyper-response of white adipose tissue is associated with an increase in GLUT4 mRNA and protein. In contrast, in skeletal muscle, a decrease in GLUT4 mRNA and a decrease (tibialis) or no change (diaphragm) in GLUT4 protein are measured, suggesting a divergent regulation by insulin of glucose transport and transporters in the 2 tissues. In rodents, brown adipose tissue is very sensitive to insulin. The response of this tissue to insulin is decreased in obese insulin-resistant fa/fa rats. Treatment with a beta-adrenergic agonist increases insulin-stimulated glucose transport, GLUT4 protein and mRNA. The data suggest that transporter synthesis can be modulated in vivo by insulin (muscle, white adipose tissue) or by catecholamines (brown adipose tissue).
Assimacopoulos-Jeannet
F
F
Laboratories de Recherches Métaboliques, University of Geneva, Switzerland.
Cusin
I
I
Greco-Perotto
R M
RM
Terrettaz
J
J
Rohner-Jeanrenaud
F
F
Zarjevski
N
N
Jeanrenaud
B
B
D000273:Adipose Tissue / Q000378:metabolism; D002001:Adipose Tissue, Brown / Q000378:metabolism; D000818:Animals; D001693:Biological Transport, Active / Q000187:drug effects; D002395:Catecholamines / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism*; D007328:Insulin / Q000494:pharmacology; D009004:Monosaccharide Transport Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D009132:Muscles / Q000378:metabolism; D051381:Rats; D011919:Rats, Inbred Strains
D002395:Catecholamines; D007328:Insulin; D009004:Monosaccharide Transport Proteins; D005947:Glucose