No evidence for expression of the insulin-regulatable glucose transporter in endothelial cells

Article Abstract:

Insulin causes increased transport of glucose, the form of sugar used for the production of energy, into muscles and fat. A family of genes has been identified that encode glucose transport molecules. One of these genes, known as the insulin-regulatable glucose transporter (IRGT) is expressed in muscles and fat, tissues where the transport of glucose is dependent on insulin. Insulin causes the movement of the glucose transporter protein from a location inside the cell to the outer membrane of the cell. It has been suggested that insulin may also be involved in the transport of glucose across the endothelial (inner layer of cells) of the capillaries (small blood vessels) in these tissues. If this was true, the IRGT protein would be present only in endothelial cells of the blood vessels in muscle and fat tissues. Studies with antibodies that react specifically to the IRGT protein show that IRGT is present in muscle and fat cells, it is located inside the cell when insulin is not present, but it is on the outer membrane when insulin is present. This change in location is especially seen in fat tissue. Studies using the electron microscope, which magnifies cells so that structural detail can be seen, also show the change in location from intracellular to the outer membrane when tissues are treated with insulin. IRGT could not be found in endothelial cells. When endothelial and fat cells were purified and separated from each other, IRGT was again found in fat cells, but not in endothelial cells. Therefore, the IRGT protein appears to allow the transport of glucose, depending on the presence of insulin, into muscle and fat cells, but not into endothelial cells of blood capillaries. (Consumer Summary produced by Reliance Medical Information, Inc.)

Muscle cells, Fat, Fats

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Expression of an insulin-regulatable glucose carrier in muscle and fat endothelial cells

Article Abstract:

Glucose is taken up into muscle and fat cells by a protein carrier or transporter, which is located in the cell membrane. The hormone insulin increases the transport of glucose into some tissues such as muscle and fat, but not in others such as liver and brain. The access of glucose to fat and muscle tissue may be restricted by endothelial cells that line the capillaries, or small blood vessels supplying blood to these tissues. In order to determine whether the endothelial cells affect the availability of glucose to fat and muscle, the endothelial cells were examined for the presence of a glucose transporter. Using antibodies, proteins that specifically bind to the glucose transporter, the presence of an abundant amount of the glucose carrier was detected in the endothelial cells. However, this endothelial cell glucose carrier was not present in the brain and liver, tissues in which insulin does not activate glucose transport. When insulin was given to animals, there was a rapid increase in the number of glucose carriers in the cell membranes of capillary endothelial cells in fat and muscle, suggesting that insulin increases the movement or translocation of glucose transporters to the cell membrane, possibly from the cell interior, where the carrier proteins are produced. The results show that endothelial cells play an active role in the regulation or control of glucose entry into insulin-sensitive tissues such as muscle and fat. (Consumer Summary produced by Reliance Medical Information, Inc.)

Medical examination, Control, Biological transport

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Dialogue between muscle and fat

Article Abstract:

Issues are presented concerning the storage of energy within fat, muscle and liver cells in mammals for use as required. The role of insulin in the storage and transportation of glucose within an organism is discussed.

Mammals

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