Effect of cold acclimation on the expression of glucose transporter Glut 4

Glucose uptake by brown adipose tissue, measured following deoxyglucose injection in vivo, was increased by 6- and 11-fold following 2 and 14 days of cold exposure, respectively. To look for the possible mechanism of these modifications, the glucose transporter Glut 4 has been characterized at the protein and mRNA levels in brown adipose tissue, skeletal muscle and white adipose tissue following cold acclimation. Crude membranes were prepared from those tissues, and Glut 4 was studied by Western blot analysis. In brown adipose tissue, the total Glut 4 amount was increased by 52 +/- 7% and by 104 +/- 12% following 2 and 14 days of cold exposure, respectively. By contrast, in white adipose tissue of 14-day-cold-exposed mice the total Glut 4 content was decreased by 42 +/- 5%. However, Glut 4 concentration, expressed per mg of membrane protein, was unchanged in both brown and white adipose tissues following cold exposure, since the membrane protein content increased in brown but decreased in white adipose tissue. No modification in Glut 4 content was observed in skeletal muscle from cold-exposed mice. Total RNA were prepared and analyzed for Glut 4, glyceraldehyde phosphate dehydrogenase (GAPDH) and actin. Glut 4 and GAPDH mRNA were increased 2-fold in brown adipose tissue from cold-exposed mice, while actin mRNA content was unmodified. Glut 4 mRNA content was not changed in white adipose tissue and skeletal muscle from cold-exposed mice. Our results suggest that Glut 4 expression is differently modulated in the three insulin-responsive tissues during cold acclimation.