Abstract
Localization of fat/muscle-type glucose transporter (GLUT4) was examined in rat soleus muscle by immunofluorescence and immunogold labeling of frozen sections. Semithin and ultrathin frozen sections were stained with anti-peptide antibodies raised against the C-terminus of GLUT4. In the muscle sections from untreated and fasted animals, GLUT4 was concentrated intracellularly in the trans-Golgi and the trans-Golgi reticulum regions. GLUT4 was also found in vesicles and tubules near the plasma membrane. Insulin administration resulted in the appearance of the GLUT4 reactivity at the plasma membrane, while a significant amount of GLUT4 remained intracellularly in vesicles and tubules and also in the Golgi. These observations suggest that vesicles and tubules near the plasma membrane and in the trans-Golgi regions are reservoirs of intracellular GLUT4 and that fusion of these vesicles and tubules with the plasma membrane upon insulin stimulation is the mechanism to supply the plasma membrane with GLUT4.
