Koenig J H, Yamaoka K, Ikeda K
Division of Neurosciences, Beckman Research Institute of the City of Hope, 1450 East Duarte Road, Duarte, CA 91010, USA.
Proc Natl Acad Sci U S A. 1998 Oct 13;95(21):12677-82. doi: 10.1073/pnas.95.21.12677.
A Ca2+-dependent synaptic vesicle-recycling pathway emanating from the plasma membrane adjacent to the dense body at the active zone has been demonstrated by blocking pinch-off of recycling membrane by using the Drosophila mutant, shibire. Exposure of wild-type Drosophila synapses to low Ca2+/high Mg2+ saline is shown here to block this active zone recycling pathway at the stage in which invaginations of the plasma membrane develop adjacent to the dense body. These observations, in combination with our previous demonstration that exposure to high Ca2+ causes "docked" vesicles to accumulate in the identical location where active zone endocytosis occurs, suggest the possibility that a vesicle-recycling pathway emanating from the active zone may exist that is stimulated by exposure to elevated Ca2+, thereby causing an increase in vesicle recycling, and is suppressed by exposure to low Ca2+ saline, thereby blocking newly forming vesicles at the invagination stage. The presence of a Ca2+-dependent endocytotic pathway at the active zone opens up the following possibilities: (i) electron microscopic omega-shaped images (and their equivalent, freeze fracture dimples) observed at the active zone adjacent to the dense body could represent endocytotic images (newly forming vesicles) rather than exocytotic images; (ii) vesicles observed attached to the plasma membrane adjacent to the dense body could represent newly formed vesicles rather than vesicles "docked" for release of transmitter.
通过使用果蝇突变体“麻木”阻断循环膜的缢断，已证明存在一条从与活性区致密体相邻的质膜发出的钙离子依赖性突触囊泡循环途径。本文显示，将野生型果蝇突触暴露于低钙/高镁盐溶液中，会在质膜在致密体附近内陷的阶段阻断这条活性区循环途径。这些观察结果，结合我们之前的证明，即暴露于高钙会使“停靠”的囊泡在活性区内吞发生的相同位置积累，表明可能存在一条从活性区发出的囊泡循环途径，该途径受到高钙暴露的刺激，从而导致囊泡循环增加，并受到低钙盐溶液暴露的抑制，从而在凹陷阶段阻断新形成的囊泡。活性区存在钙离子依赖性内吞途径开启了以下可能性：（i）在与致密体相邻的活性区观察到的电子显微镜下的ω形图像（及其等效的冷冻断裂凹坑）可能代表内吞图像（新形成的囊泡）而非外排图像；（ii）在与致密体相邻的质膜上观察到的附着囊泡可能代表新形成的囊泡，而非为释放递质而“停靠”的囊泡。
