A series of aminotriarylmethane dyes were examined for binding to the nicotinic acetylcholine receptor (AChR) from Torpedo californica. Several compounds were found to bind to the noncompetitive antagonist site of the AChR as demonstrated by inhibition of [3H]phencyclidine binding; apparent KD values ranged from 50 nM to >100 microM. One dye with high affinity, crystal violet, revealed a greate...

The acetylcholine receptor (AChR)-associated protein rapsyn is essential for neuromuscular synapse formation and clustering of AChRs, but its mode of action remains unclear. We have investigated whether agrin, a key nerve-derived synaptogenic factor, influences rapsyn-AChR interactions and how this affects clustering and cytoskeletal linkage of AChRs. By precipitating AChRs and probing for asso...

lustering of acetylcholine receptors (AChRs) is a critical step in neuromuscular synaptogenesis, and is induced by agrin and laminin which are thought to act through different signaling mechanisms. We addressed whether laminin redistributes postsynaptic proteins and requires key elements of the agrin signaling pathway to cause AChR aggregation. In myotubes, laminin-1 rearranged dystroglycans an...

To investigate the role of thymic myoid cells in the pathogenesis of myasthenia gravis (MG), mRNA of nonneoplastic thymuses from eight MG patients was analyzed by dot blot hybridization for the occurrence of acetylcholine receptor (AChR) subunit transcripts, using the five AChR-subunit cDNAs (alpha, beta, gamma, delta, and epsilon) as probes. Attention was particularly paid to the gamma- and ep...

Agrin triggers signaling mechanisms of high temporal and spatial specificity to achieve phosphorylation, clustering, and stabilization of postsynaptic acetylcholine receptors (AChRs). Agrin transiently activates the kinase MuSK; MuSK activation has largely vanished when AChR clusters appear. Thus, a tyrosine kinase cascade acts downstream from MuSK, as illustrated by the agrin-evoked long-lasti...

BACKGROUND Myasthenia gravis is a potentially serious but treatable muscle disease caused by autoantibodies directed at the acetylcholine receptor (AChR) on the postsynaptic membrane of the neuromuscular junction. There is anecdotal evidence that the diagnosis is sometimes missed in older patients. OBJECTIVE To examine the incidence and age distribution of positive AChR antibodies in samples ...

Postnatal stabilization and maturation of the postsynaptic membrane are important for development and function of the neuromuscular junction (NMJ), but the underlying mechanisms remain poorly characterized. We examined the role of Src-family kinases (SFKs) in vivo. Electroporation of kinase-inactive Src constructs into soleus muscles of adult mice caused NMJ disassembly: acetylcholine receptor ...

Myasthenia gravis is usually caused by autoantibodies to the acetylcholine receptor (AChR). The AChR is clustered and anchored in the postsynaptic membrane of the neuromuscular junction (NMJ) by a cytoplasmic protein called rapsyn. We previously showed that resistance to experimental autoimmune myasthenia gravis (EAMG) in aged rats correlates with increased rapsyn concentration at the NMJ. It i...

Chick ciliary ganglion neurons receive innervation from a single source, the accessory oculomotor nucleus (AON), and nicotinic ACh receptors (AChRs) mediate chemical synaptic transmission through the ganglion. Previous experiments examining the developmental expression of AChRs in embryonic chick ciliary ganglion neurons in situ have shown that AChR levels increase substantially in the neurons ...

Cultured rat myotubes develop high concentrations of acetylcholine receptors (AChR) in specialized areas of attachment to their substrate. We examined the ultrastructure of identified AChR clusters by quick-freeze, deep-etch, rotary replication or by thin sectioning of whole myotubes fixed in the presence of saponin and tannic acid to preserve the cytoskeleton. Our findings show that AChR clust...