ACETYLCHOLINE-RECEPTOR CLUSTERING IN C2 MUSCLE-CELLS REQUIRES CHONDROITIN SULFATE

Proteoglycans have been implicated in the clustering of acetylcholine receptors (AChRs) on cultured myotubes and at the neuromuscular juncti on. We report that the presence of chondroitin sulfate is associated w ith the ability of cultured myotubes to form spontaneous clusters of A ChRs. Three experimental manipulations of wild type C2 cells in cultur e were found to affect both glycosaminoglycans (GAGs) and AChR cluster ing in concert. Chlorate was found to have dose-dependent negative eff ects both on GAG sulfation and on the frequency of AChR clusters. When extracellular calcium was raised from 1.8 to 6.8 mM in cultures of wi ld-type C2 myotubes, increases were observed both in the level of cell layer-associated chondroitin sulfate and in the frequency of AChR clu sters. Culture of wild-type C2 myotubes in the presence of chondroitin ase ABC eliminated cell layer-associated chondroitin sulfate while lea ving heparan sulfate intact and simultaneously prevented the formation of AChR clusters. Treatment with either chlorate or chondroitinase in hibited AChR clustering only if begun prior to the spontaneous formati on of clusters. We propose that chondroitin sulfate plays an essential role in the initiation of AChR clustering and in the early events of synapse formation on muscle. (C) 1995 John Wiley & Sons, Inc.