Parsons T D, Coorssen J R, Horstmann H, Almers W
Abteilung Molekulare Zellforschung, Max-Planck Institut fur Medizinische Forschung, Heidelberg, Federal Republic of Germany.
Neuron. 1995 Nov;15(5):1085-96. doi: 10.1016/0896-6273(95)90097-7.
Ca(2+)-triggered exocytosis was studied in single rat melanotrophs and bovine chromaffin cells by capacitance measurements. Sustained exocytosis required MgATP, but even in the absence of MgATP, Ca2+ could trigger exocytosis of 2700 granules in a typical melanotroph and of 840 granules in a chromaffin cell. Granules undergoing ATP-independent exocytosis were similar in number to those appearing docked to the plasmalemma in quickly frozen unfixed sections (3300 in a melanotroph and 830 in a chromaffin cell). Most exocytosis required tens of seconds, but a small pool of granules was released in tens of milliseconds. Evidently, only a small subset of docked granules is rapidly releasable. We suggest that, temporally, the last ATP-dependent step in exocytosis is closely associated with docking and that docked granules reach fusion competence only after subsequent steps.
通过电容测量法，在单个大鼠黑素细胞和牛嗜铬细胞中研究了Ca(2+)触发的胞吐作用。持续性胞吐作用需要MgATP，但即使在没有MgATP的情况下，Ca2+也能触发典型黑素细胞中2700个颗粒和嗜铬细胞中840个颗粒的胞吐作用。经历不依赖ATP的胞吐作用的颗粒数量与快速冷冻未固定切片中停靠在质膜上的颗粒数量相似（黑素细胞中为3300个，嗜铬细胞中为830个）。大多数胞吐作用需要数十秒，但一小部分颗粒在数十毫秒内释放。显然，只有一小部分停靠的颗粒能够快速释放。我们认为，在时间上，胞吐作用中最后一个依赖ATP的步骤与停靠密切相关，并且停靠的颗粒只有在后续步骤之后才达到融合能力。
