Final answer:
GLUT-4, an insulin-sensitive glucose transporter, is expressed primarily in muscle cells and adipose tissue, allowing increased glucose uptake from the blood into these cells in response to insulin.
Step-by-step explanation:
The insulin-sensitive glucose transporter, GLUT-4, is primarily expressed in two types of tissue: muscle cells and adipose tissue.
Upon the presence of insulin, the GLUT-4 transporters are mobilized to the plasma membrane of these cells. Insulin activates insulin receptors, which in turn sets off a cascade of phosphorylation events involving IRS-1. This cascade results in GLUT-4-containing vesicles fusing with the plasma membrane, thereby increasing glucose uptake from the blood. The role of insulin and GLUT-4 is critical for regulating blood sugar levels and storing glucose within cells as glycogen.
GLUT proteins serve different functions in different tissues, with variants like SGLT operating in the kidneys and small intestine. However, GLUT-4 is unique in its sensitivity to insulin, which underscores its special role in tissues like skeletal muscle fibers and fat cells, where glucose uptake is significantly increased following insulin signaling.