Effective interactions between cells and their environment often rely on the creation, maintenance, and regulation of specialized membrane domains. Such domains are typically comprised of selected cytoskeletal, signaling, and adhesion molecules. The task confronting the cell is to deploy these elements into functional units in the right places at the right times. Skeletal muscle cells offer some of the best examples of such selective spatiotemporal regulation of cell surface specializations. For example, the postsynaptic apparatus occupies only about 0.1% of the plasma membrane, yet possesses all of the machinery necessary for rapid communication with the nerve terminal. Most notably, the density of acetylcholine receptors (AChRs) in this domain exceeds 10,000/μm2 (Colledge and Froehner 1998).
The large expanse of extrasynaptic membrane, which in normal muscle bears only about 10 AChRs/μm2, is nonetheless specialized in its...
