Measurement of Contraction-Stimulated GLUT-4 Translocation in Isolated Skeletal Muscle

The ability of cells to transport glucose through the plasma membrane and into the cell for use in metabolism is of prime importance in cellular metabolism. This process occurs through a family of glucose transport proteins (1 ). In insulin-sensitive cells, such as heart, skeletal muscle, and adipose tissue, glucose transport is mediated by two members of this family, termed GLUT-1 and GLUT-4. Of these two transporters, GLUT-1 is found primarily in the plasma membrane and functions in regulation of basal glucose transport. However, in the basal non-stimulated state, GLUT-4 is found primarily in an intracellular storage site, and in response to insulin GLUT-4-containing vesicles, they translocate to the plasma membrane, where they dock, fuse, and allow the exposed GLUT-4 transporters to transport glucose (2 ). In fact, a major feature of type 2 diabetes mellitus (NIDDM) is a defect in insulin-stimulated GLUT-4 translocation to the plasma membrane in skeletal muscle. Interestingly, in skeletal muscle, contractile activity possesses an insulin-like ability to stimulate GLUT-4 translocation, although it is unclear if the same population of GLUT-4 vesicles are recruited by both stimuli (3 ). Therefore, the ability to measure and quantify GLUT-4 translocation is of major importance in investigating this disease.