Wu L G, Betz W J
Department of Physiology, University of Colorado Health Science Center, Denver 80262, USA.
Biophys J. 1998 Jun;74(6):3003-9. doi: 10.1016/S0006-3495(98)78007-5.
We measured the time courses of two key components of the synaptic vesicle cycle during recovery from synaptic depression under different conditions, and used this and other information to create a kinetic model of the vesicle cycle. End plate potential (EPP) amplitudes were used to follow recovery from synaptic depression after different amounts of tetanic stimulation. This provided an estimate of the time course of vesicle mobilization from the reserve pool to the docked (readily releasable) pool. In addition, FM1-43 was used to measure the rate of membrane retrieval after tetanic stimulation, and the amount of membrane transferred to the surface membrane. This provided a measure of the rate of refilling of the reserve pool with recycled vesicles. The time courses of both synaptic depression and endocytosis were slowed by prolonged tetanic stimulation. This behavior could be fitted by a simple model, assuming a first-order kinetics for both vesicle endocytosis and mobilization. The results show that a nearly 20-fold decrease in the rate constant of endocytosis greatly delays refilling of the depleted reserve pool. However, to fully account for the slower recovery of depression, a decrease in the rate constant of vesicle mobilization from the reserve pool of about sixfold is also required.
我们在不同条件下从突触抑制恢复过程中测量了突触小泡循环的两个关键成分的时间进程，并利用这些及其他信息创建了一个小泡循环的动力学模型。终板电位（EPP）幅度用于追踪不同程度强直刺激后从突触抑制中的恢复情况。这提供了从储备池到停靠（易于释放）池的小泡动员时间进程的估计值。此外，FM1-43用于测量强直刺激后的膜回收速率以及转移到表面膜的膜量。这提供了用回收小泡重新填充储备池速率的一种测量方法。长时间的强直刺激会减缓突触抑制和内吞作用的时间进程。这种行为可以用一个简单的模型来拟合，假设小泡内吞作用和动员均为一级动力学。结果表明，内吞作用速率常数近20倍的下降极大地延迟了耗尽的储备池的重新填充。然而，为了充分解释抑制恢复较慢的情况，还需要储备池中小泡动员速率常数下降约6倍。
