Acetylcholine-induced cation translocation across cell membranes and inactivation of the acetylcholine receptor: chemical kinetic measurements in the millisecond time region.
Acetylcholine-induced cation translocation across cell membranes and inactivation of the acetylcholine receptor: chemical kinetic measurements in the millisecond time region.
复制标题
乙酰胆碱诱导的阳离子跨细胞膜易位和乙酰胆碱受体失活：毫秒时间区域的化学动力学测量。
DOI：
10.1073/pnas.78.6.3318
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发表时间：
1981
影响因子：
11.1
通讯作者：
Hess,GP
中科院分区：
文献类型：
--
作者：
Cash,DJ;Aoshima,H;Hess,GP
乙酰胆碱诱导的跨膜无机离子通量和乙酰胆碱受体的失活进行了测量，在pH 7.0，1摄氏度，超过5000倍的浓度范围内的乙酰胆碱。使用从Electrophorus electricus制备的含受体的electroplax膜囊泡和猝灭流技术，允许在2毫秒至1分钟的时间区域内测量通量。进行了五种不同的测量：（i）受体活性状态下的离子移位速率，（ii）活性和非活性受体状态平衡后较慢的离子移位速率，（iii）失活速率，（iv）受体活性和非活性形式之间的平衡，以及（v）失活受体的再活化。在受体控制的离子通量的步骤的动力学遵循单指数速率定律，和简单的分析表达式，其配体浓度依赖性可以使用。因此，可以评估将配体结合步骤与离子易位相关联的方案中的速率和平衡常数。结果发现，受体控制的离子迁移的浓度范围内的依赖性研究服从综合速率方程的基础上提出的机制。失活前的通量率约为10（7）离子sec-1/受体，这与肌细胞中的电生理学测量值相当。当受体被乙酰胆碱饱和时，失活的半衰期约为100 msec。离子迁移的比反应速率（J）为3 × 10（7）M ~（-1）秒~（-1）。结果支持最低限度的反应机制先前提出的实验中使用的氨甲酰胆碱的基础上。
Acetylcholine-induced flux of inorganic ions across membranes and inactivation of the acetylcholine receptor were measured at pH 7.0, 1 degrees C, over a 5000-fold concentration range of acetylcholine. Receptor-containing electroplax membrane vesicles prepared from Electrophorus electricus and a quench-flow technique were used, allowing flux to be measured in the 2-msec to 1-min time region. Five different measurements were made: (i) rate of ion translocation with the active state of the receptor, (ii) rate of the slower ion translocation after equilibration of active and inactive receptor states, (iii) rate of inactivation, (iv) equilibrium between active and inactive forms of the receptor, and (v) reactivation of inactivated receptor. The kinetics of the steps in the receptor-controlled ion flux follow single-exponential rate laws, and simple analytical expressions for their ligand concentration dependence can be used. Thus, the rate and equilibrium constants in a scheme that relates the ligand binding steps to ion translocation could be evaluated. It was found that the dependence of the receptor-controlled ion translocation over the concentration range investigated obeys the integrated rate equation based on the proposed mechanism. The flux rate before inactivation was approximately 10(7) ions sec-1 per receptor, which is comparable with that measured electrophysiologically in muscle cells. The half-time of inactivation is approximately 100 msec when the receptor is saturated with acetylcholine. The specific reaction rate of the ion translocation (J) is 3 X 10(7) M-1 sec-1. The results support a minimum reaction mechanism previously proposed on the basis of experiments in which carbamylcholine was used.