Figure 1.

Schematic figure showing the T-tubule (T-T) system and its high cholesterol content compared with the surface membrane (sarcolemma, see inserts). Note the main proteins of the EC coupling complex and the sites of GLUT4 translocation. In response to insulin, the GLUT4 transporters translocate mainly to the T-tubule system, where EC coupling takes place, and also to the surface membrane region. Modifications of cholesterol content affect both EC coupling and GLUT4 mediated glucose transport in skeletal muscle. ↑: increment; ↓: decrease; ?: unknown effect.