Molecular mechanisms involved in GLUT4 translocation in muscle during insulin and contraction stimulation.

Studies in mammalian cells have established the existence of numerous intracellular signaling cascades that are critical intermediates in the regulation of various biological functions. Over the past few years considerable research has shown that many of these signaling proteins are expressed in skeletal muscle. However, the detailed mechanisms involved in the regulation of glucose transporter (GLUT4) translocation from intracellular compartments to the cell surface membrane in response to insulin and contractions in skeletal muscle are not well understood. In the present essay we report three different approaches to unravel the GLUT4 translocation mechanism: 1. specific pertubation of the insulin and/or contraction signaling pathways; 2. characterization of the protein composition of GLUT4-containing vesicles with the expectation that knowledge of the constituent proteins of the vesicles may help in understanding their trafficking; 3. degree of co-immunolocalization of the GLUT4 glucose transporters with other membrane marker proteins assessed by immunofluorescense and electron microscopy.