Shyng S L, Salpeter M M
Section of Neurobiology and Behavior, Cornell University, Ithaca, New York 14853.
J Neurosci. 1990 Dec;10(12):3905-15. doi: 10.1523/JNEUROSCI.10-12-03905.1990.
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.
在神经肌肉接头（NMJ）去神经支配后，已证明突触后膜中共存着两种降解速率不同的乙酰胆碱受体（AChRs）。其中一种由去神经支配之前插入质膜的降解缓慢的原始AChRs组成，其降解半衰期（t1/2）约为8天。这种降解速率在去神经支配后加快（至t1/2约为3天），但可通过重新神经支配使其减慢回到去神经支配前的速率。第二种是降解迅速的新AChRs，在去神经支配后取代NMJ处正在降解的原始AChRs，类似于胚胎AChRs，t1/2约为1天。在本研究中，我们报告称，重新神经支配后，这些新的接头AChRs的降解速率在3 - 6个半衰期内未发生改变。我们还进一步报告，去神经支配的肌肉中可能也会合成少量（少于10%）降解缓慢的AChRs（t1/2约为3天）。我们认为，与重新神经支配对原始的、降解缓慢的AChRs的作用不同，它不会调节降解迅速的新接头AChRs的降解速率。它仅仅调节在NMJ处合成并插入的快速降解与缓慢降解AChRs的比例。
