Development of synaptic specializations on Xenopus laevis muscle cells in culture

Embryonic Xenopus muscle cells grown in culture develop patches of high acetylcholine receptor (AChR) density which can be visualized using fluorescent -bungarotoxin. In the present study it was found that these AChR patches often occur at sites of strong adhesion with the culture dish and remain in a fixed position, relatively unchanged for several days. Discrete patches of cholinesterase (ChE) also develop, often at the same sites as the AChR patches, even if the muscle cells have never been innervated in vivo. ChE, like AChRs, also becomes localized at sites of nerve-muscle contact in cultures grown with spinal cord cells whether or not neuromuscular transmission is blocked by curare. The results further indicate that in addition to directing AChR and ChE localization to the site of nerve-muscle contact, the nerve prevents the formation and reduces the survival of AChR and ChE patches elsewhere on the muscle cell