Reiness C G, Hogan P G, Marshall J M, Hall Z W
Prog Clin Biol Res. 1977;15:207-15.
During development and after both denervation and reinnervation in adult mammalian skeletal muscle, the level of acetylcholine (ACh) receptors in the extrajunctional membrane undergoes wide variation. We have determined the rate of extrajunctional receptor degradation in denervated muscles in organ culture under a variety of conditions by measuring the rate at which alpha-bungarotoxin bound to the receptors is degraded. Direct electrical stimulation of muscles for several days dramatically reduced the levels of extrajunctional ACh sensitivity, and also reduced the rate of receptor degradation. Since the effect of activity on the rate of receptor degradation is in the opposite direction of the observed change in receptor levels, we conclude that activity must also decrease the rate of receptor synthesis. Receptor degradation was also examined in muscles at various times after denervation. The half-time of degradation increased from approximately 7 hr at 2-5 days after denervation to approximately 14 hr at 10-14 days. Hypophysectomy, which decreases the average rate of protein degradation in muscle, also decreased the rate of extrajunctional receptor degradation, but thyroxine, which restores the normal rate of overall protein breakdown in hypophysectomized animals, did not affect receptor breakdown. Since hypophysectomy did not increase the level of extrajunctional ACh receptors, it must also affect ACh receptor synthesis.
在成年哺乳动物骨骼肌发育期间以及去神经支配和再支配之后，接头外膜中乙酰胆碱（ACh）受体的水平会发生很大变化。我们通过测量与受体结合的α-银环蛇毒素的降解速率，在多种条件下测定了器官培养中去神经肌肉接头外受体的降解速率。对肌肉进行数天的直接电刺激可显著降低接头外ACh敏感性水平，同时也降低了受体降解速率。由于活性对受体降解速率的影响与观察到的受体水平变化方向相反，我们得出结论，活性也必然降低了受体合成速率。我们还研究了去神经后不同时间肌肉中的受体降解情况。降解半衰期从去神经后2 - 5天的约7小时增加到10 - 14天的约14小时。垂体切除会降低肌肉中蛋白质降解的平均速率，同时也降低了接头外受体的降解速率，但甲状腺素（能恢复垂体切除动物中整体蛋白质分解的正常速率）并未影响受体分解。由于垂体切除并未增加接头外ACh受体的水平，所以它必然也影响ACh受体的合成。
