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Increased insulin levels cause the uptake of glucose into the cells. GLUT4 is stored in the cell in transport vesicles, and is quickly incorporated into the plasma membrane of the cell when insulin binds to membrane receptors. [24] Under conditions of low insulin, most GLUT4 is sequestered in intracellular vesicles in muscle and fat cells.
When the insulin binds to these alpha subunits, 'glucose transport 4' (GLUT4) is released and transferred to the cell membrane to regulate glucose transport in and out of the cell. With the release of GLUT4, the allowance of glucose into cells is increased, and therefore the concentration of blood glucose might decrease.
This hormone, insulin, causes the liver to convert more glucose into glycogen (this process is called glycogenesis), and to force about 2/3 of body cells (primarily muscle and fat tissue cells) to take up glucose from the blood through the GLUT4 transporter, thus decreasing blood sugar.
Circulating insulin also affects the synthesis of proteins in a wide variety of tissues. It is thus an anabolic hormone, promoting the conversion of small molecules in the blood into large molecules in the cells. Low insulin in the blood has the opposite effect, promoting widespread catabolism, especially of reserve body fat.
GLUT4 transporters are insulin sensitive, and are found in muscle and adipose tissue. As muscle is a principal storage site for glucose and adipose tissue for triglyceride (into which glucose can be converted for storage), GLUT4 is important in post-prandial uptake of excess glucose from the bloodstream. Moreover, several recent papers show ...
The insulin receptor (IR) is a transmembrane receptor that is activated by insulin, IGF-I, IGF-II and belongs to the large class of receptor tyrosine kinase. [5] Metabolically, the insulin receptor plays a key role in the regulation of glucose homeostasis; a functional process that under degenerate conditions may result in a range of clinical manifestations including diabetes and cancer.
Levels in cell membranes are increased by reduced glucose levels and decreased by increased glucose levels. GLUT1 expression is upregulated in many tumors. GLUT2: Is a bidirectional transporter, allowing glucose to flow in 2 directions. Is expressed by renal tubular cells, liver cells and pancreatic beta cells.
In addition, Rab-4B is thought to be important in the insulin pathway with its involvement with GLUT4 trafficking. GLUT4 plays a crucial role in maintaining glucose balance, and is primarily found in cells that respond to insulin for glucose uptake, such as adipocytes. Upon stimulation by insulin, RAB-4B is activated and able to contribute to ...