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Volume 17, Number 21,
Issue of November 1, 1997
pp. 8194-8200
Copyright ©1997 Society for Neuroscience
Acetylcholine Receptors in Innervated Muscles of Dystrophic
mdx Mice Degrade as after Denervation
Received May 29, 1997; revised Aug. 20, 1997; accepted Aug. 21, 1997.
Rufeng Xu and
Miriam M. Salpeter
Section of Neurobiology and Behavior, Cornell University, Ithaca,
New York 14853
Acetylcholine receptors (AChRs) are present at the top of the
postsynaptic membrane of the neuromuscular junction (NMJ) at very high
density, possibly anchored to cytoskeletal elements. The present study
investigated whether AChR degradation is affected in animals lacking
dystrophin, a protein that is an integral part of the cytoskeletal
complex and is missing in Duchenne muscular dystrophy. The animal model
for Duchenne muscular dystrophy, the mutant mdx mouse,
was used to determine whether disruption of the cytoskeleton, caused by
the absence of dystrophin, affects AChR degradation. Of the two
populations of junctional AChRs, Rs (expressed in innervated adult
muscles) and Rr (expressed in embryonic or denervated muscles), only Rs
are affected in mdx animals. In innervated
mdx soleus, diaphragm, and sternomastoid muscles, the
AChRs have an accelerated degradation rate
(t1/2 of ~3-5 d), similar to that
acquired by Rs in control muscles after denervation. The Rs in
mdx NMJs do not accelerate further when the muscles are
denervated. The absence of dystrophin does not affect the degradation
rate of the Rr AChRs (t1/2 of 1 d), which are expressed after denervation in mdx as in
control muscles. These results suggest that dystrophin or an intact
cytoskeletal complex may be required for neuronal stabilization of Rs
receptors at the adult neuromuscular junctions.
Key words:
cAMP;
forskolin;
soleus;
diaphragm;
sternomastoid;
turnover
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