GLUT2 (and GLUT1) is found in liver and is always present in the plasma membrane of
hepatocytes. GLUT3 is always present in the plasma membrane of certain brain cells. GLUT4 is
normally sequestered in vesicles in cells of muscle and adipose tissue and enters the plasma
membrane only in response to insulin. Thus, liver and brain can take up glucose from blood
regardless of insulin level, but muscle and adipose tissue take up glucose only when insulin
levels are elevated in response to high blood glucose.