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J Cell Biol ; 153(7): 1441-52, 2001 Jun 25.
Article in English | MEDLINE | ID: mdl-11425874

ABSTRACT

Aggregation of acetylcholine receptors (AChRs) in muscle fibers by nerve-derived agrin plays a key role in the formation of neuromuscular junctions. So far, the effects of agrin on muscle fibers have been studied in culture systems, transgenic animals, and in animals injected with agrin--cDNA constructs. We have applied purified recombinant chick neural and muscle agrin to rat soleus muscle in vivo and obtained the following results. Both neural and muscle agrin bind uniformly to the surface of innervated and denervated muscle fibers along their entire length. Neural agrin causes a dose-dependent appearance of AChR aggregates, which persist > or = 7 wk after a single application. Muscle agrin does not cluster AChRs and at 10 times the concentration of neural agrin does not reduce binding or AChR-aggregating activity of neural agrin. Electrical muscle activity affects the stability of agrin binding and the number, size, and spatial distribution of the neural agrin--induced AChR aggregates. Injected agrin is recovered from the muscles together with laminin and both proteins coimmunoprecipitate, indicating that agrin binds to laminin in vivo. Thus, the present approach provides a novel, simple, and efficient method for studying the effects of agrin on muscle under controlled conditions in vivo.


Subject(s)
Agrin/administration & dosage , Agrin/metabolism , Muscle, Skeletal/drug effects , Muscle, Skeletal/metabolism , Agrin/isolation & purification , Animals , Cell Line , Chickens , Dose-Response Relationship, Drug , Electric Stimulation , Humans , Injections, Intramuscular , Laminin/metabolism , Muscle Denervation , Muscle Fibers, Skeletal/drug effects , Muscle Fibers, Skeletal/metabolism , Muscle, Skeletal/innervation , Precipitin Tests , Protein Binding/physiology , Protein Isoforms/administration & dosage , Protein Isoforms/isolation & purification , Protein Isoforms/metabolism , Rats , Receptor Aggregation/drug effects , Receptors, Cholinergic/metabolism , Recombinant Proteins/metabolism , Recombinant Proteins/pharmacology
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