Association of the Postsynaptic 43K Protein with Sites of Clustered and Diffusely-Distributed Acetylcholine Receptors

Abstract

The formation of the rat neuromuscular junction is a complicated, multistep process that is initiated when the growing nerve first makes contact with embryonic muscle (1). One of the first and most important changes that occurs is an alteration in the distribution of acetylcholine receptors (AChR). Diffusely-distributed receptors become clustered at sites immediately adjacent to the nerve terminal. In adult muscle, receptors are located almost exclusively at synaptic sites at a density of 8–10,000 receptors per square micron of membrane surface (2). Since AChR are multisubunit, transmembrane proteins that are inherently capable of diffusion within the plane of the membrane, special mechanisms must exist that anchor receptors at appropriate sites across the synaptic gap from sites of transmitter release.