Albuquerque E X, Barnard E A, Porter C W, Warnick J E
Proc Natl Acad Sci U S A. 1974 Jul;71(7):2818-22. doi: 10.1073/pnas.71.7.2818.
In various skeletal muscles, the mean density of acetylcholine receptors in the muscle postsynaptic membrane is constant at about 8700 per mum(2), even though the overall size of an endplate ranged from 400 mum(2) to 1300 mum(2) in these muscles. This measurement was by electron microscope autoradiography of alpha-[(3)H]bungarotoxin binding sites; only one-half of these, however, appear to be true active centers of the acetylcholine receptor. The highest density of these receptors is on the juxtaneuronal regions of the postsynaptic membrane, and their density in the depths of the fold is less than one quarter of that at the tips. A maximum sensitivity to externally applied acetylcholine, about 3000-5000 mV/nC, is found in diverse types of endplates when truly focal recording is achieved. This acetylcholine sensitivity appears to be determined by the local density of receptors in the membrane, and not by their total number at the endplate. A quantal efficiency term is also disclosed. The maximal sensitivity per molecule obtainable by microiontophoresis of acetylcholine is 5-10% of that operative when a quantum reacts. When acetylcholine is released from a vesicle, in contrast to its application from outside, geometric factors are more favorable. Consideration of the local packing density, acetylcholine molecule numbers, and the current flow when one quantum of acetylcholine interacts at the membrane suggests that one, or possibly two, activated receptor active centers are linked to one open gate of the ionic conductance modulator.
在各种骨骼肌中，肌肉突触后膜上乙酰胆碱受体的平均密度恒定在每平方微米约8700个，尽管在这些肌肉中终板的总面积范围为400平方微米至1300平方微米。该测量是通过对α-[(3)H]银环蛇毒素结合位点进行电子显微镜放射自显影；然而，其中只有一半似乎是乙酰胆碱受体的真正活性中心。这些受体的最高密度位于突触后膜的近神经元区域，其在褶皱深处的密度不到尖端密度的四分之一。当实现真正的焦点记录时，在不同类型的终板中发现对外源性乙酰胆碱的最大敏感性约为3000 - 5000 mV/nC。这种乙酰胆碱敏感性似乎由膜中受体的局部密度决定，而非终板上受体的总数。还揭示了一个量子效率项。通过乙酰胆碱微离子电泳可获得的每个分子的最大敏感性是一个量子反应时的5% - 10%。与从外部施加乙酰胆碱相比，当乙酰胆碱从囊泡释放时，几何因素更有利。考虑局部堆积密度、乙酰胆碱分子数量以及当一个乙酰胆碱量子在膜上相互作用时的电流流动表明，一个或可能两个活化的受体活性中心与离子电导调节剂的一个开放门相连。
