Journal of Neuroscience, Vol 10, 3905-3915, Copyright © 1990 by Society for Neuroscience
Effect of reinnervation on the degradation rate of junctional acetylcholine receptors synthesized in denervated skeletal muscles
SL Shyng and MM Salpeter
Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853.
Two populations of ACh receptors (AChRs) with different degradation rates
have been shown to coexist in the postsynaptic membrane after denervation
of the neuromuscular junction (NMJ). One population, consisting of the
slowly degrading original AChRs inserted into the plasma membrane prior to
denervation, has a degradation half-life (t1/2) of approximately 8 d. This
degradation rate accelerates after denervation (to a t1/2 approximately 3
d), but can be decelerated back to the predenervation rate by
reinnervation. The second population, the rapidly degrading new AChRs,
which replace the degrading original AChRs at the NMJ after denervation,
resembles embryonic AChRs, with a t1/2 of approximately 1 d. In the present
study, we report that the degradation rate of these new junctional AChRs is
unaltered for 3-6 half-lives after reinnervation. We further report that a
small amount (less than 10%) of slowly degrading AChRs (t1/2 approximately
3 d) may also be synthesized in denervated muscle. We suggest that, unlike
its effect on the original, slowly degrading AChRs, reinnervation does not
modulate the degradation rate of the rapidly degrading new junctional
AChRs. It merely regulates the ratio of rapidly to slowly degrading AChRs
being synthesized and inserted at the NMJ.
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