Synaptic vesicle recycling and changes in synaptic efficacy

我们希望阐明突触小泡内吞作用的机制，以及内吞作用在果蝇神经肌肉接头突触传递中的作用。突触小泡的胞吞作用和内吞作用被认为是由相同的钙离子内流控制的，因为胞吞作用总是伴随着胞吐作用，而且这两个过程都需要外部的钙离子。我们发现，钙通道阻断剂La3+和氟桂利嗪抑制内吞作用而不影响胞吐作用，而蜘蛛毒素钙通道阻断剂PLTXII则主要抑制胞吐作用。这些结果表明，钙离子通过不同的途径内流控制胞吐和内吞作用。使用钙通道阻滞剂，我们发现了两种不同的内吞作用：活跃区内吞作用和非活跃区内吞作用。活动区内吞作用是胞苷非依赖性的，在高活性的早期起作用，而非活动区的内吞作用是胞苷依赖的，在高活性的后期起作用。这些结果表明，高活性的突触传递是由两种类型的内吞作用协调维持的。

We wish to clarify mechanisms of endocytosis of synaptic vesicles and roles of endocytosis in synaptic transmission at Drosophila Neuromuscular junction.1. It has been believed that exocytosis and endocytosis of synaptic vesicles are controlled by the same Ca2+ influx, because endocytosis always follows exocytosis and both process require external Ca2+. We found that La3+ and fulunarizine, Ca2+ channel blocker, depressed endocytosis without affecting exocytosis, while PLTXII, Ca2+ channel blocker from spider toxin, depressed predominantly exocytosis. These results suggest that Ca2+ influx through distinct routes controls exocytosis and endocytosis.2. Using Ca2+ channel blockers, we revealed two distinct endocytosis; active-zone endocytosis and non-active-zone endocytosis. Active-zone endocytosis is clathrin-independent and operate early phase of high activity, whereas non-active-zone endocytosis is clathrin-dependent and works in late phase of high activity. These results suggest that synaptic transmission at high activity is maintained coordinately by two types of endocytosis.