Until a mobilization signal is received, glucose transporter 4 (GLUT4) proteins are conserved within muscle and fat cells through a recycling process that cycles them between the plasma membrane and a vesicle storage pool. Clicking on each of the
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GLUT4 proteins leave the Golgi apparatus embedded in a transport vesicle.
When glucose levels outside of the cell are low, only a small amount of the GLUT 4 is found in the plasma membrane.
The GLUT4 transporters in the plasma membrane pool are needed to move any available low levels of glucose into the cell.
During such periods of low glucose availability, the majority of the GLUT4 within the cell is found in GLUT4 storage vesicles (GSVs). This is a group of vesicles that cluster together.
When GLUT4 proteins from the plasma membrane bud off and move to the GSV pool, they are replaced by the movement of vesicles from the GSV pool back to the plasma membrane.
Recycling GLUT4 proteins by way of membrane vesicles balances the cell's current need for the GLUT4 protein with the ability to rapidly mobilize available GLUT4 when glucose levels rise.