Division of Neurobiology, Department of Physiology, University of California, San Francisco, School of Medicine, San Francisco, California 94143, USA.
Dev Biol. 1981 Jun;84(2):247-54. doi: 10.1016/0012-1606(81)90392-4.
The turnover of acetylcholine receptors (AChRs) was studied at developing motor endplates in embryonic rat diaphragm and at newly formed ectopic endplates in soleus muscles of adult rats. After the receptors were labeled in situ with 125I-alpha-bungarotoxin, the rate of loss of bound toxin was determined by autoradiography of single muscle fibers and was used to calculate the turnover time of AChRs. A new, convenient method for preparing large numbers of single muscle fibers is described. AChRs in extrajunctional regions of embryonic diaphragms turn over with a short half-time (24 hr) similar to that of AChRs in cultured myotubes and of extrajunctional AChRs in denervated adult muscle. AChRs in newly formed clusters in developing muscle and in ectopically innervated adult muscle also turn over with short half-times. Within a few days, however, the turnover time increases to values characteristic of adult junctional receptors (6-10 days). Transection of the nerve at newly formed ectopic endplates prevents the change. The metabolic stabilization of AChRs at motor endplates in rat muscles is thus a relatively early event in synapse formation; it coincides neither with the clustering of receptors, which precedes it, nor with the decrease in AChR channel open time which has been shown to occur postnatally.
乙酰胆碱受体（AChR）的周转率在胚胎大鼠膈肌发育中的运动终板和成年大鼠比目鱼肌中新形成的异位终板中进行了研究。在受体用 125I-α-银环蛇毒素原位标记后，通过单根肌纤维的放射自显影测定结合毒素的损失率，并用于计算 AChR 的周转率。描述了一种新的、方便的制备大量单根肌纤维的方法。在胚胎膈肌的关节外区域的 AChR 周转率半衰期短（24 小时），与培养的肌管中的 AChR 和去神经成年肌肉中的关节外 AChR 相似。在发育中的肌肉中新形成的簇和异位神经支配的成年肌肉中的 AChR 也以短半衰期进行周转。然而，在几天内，周转率增加到具有成年连接受体特征的时间（6-10 天）。在新形成的异位终板处切断神经可防止这种变化。因此，大鼠肌肉运动终板处 AChR 的代谢稳定性是突触形成中相对较早的事件；它既不与受体的聚集同时发生，也不与已经表明发生在出生后的 AChR 通道开放时间减少同时发生。
