Alvarez de Toledo G, Fernandez J M
Department of Physiology, School of Medicine, University of Pennsylvania, Philadelphia 19104-6085.
J Gen Physiol. 1990 Mar;95(3):397-409. doi: 10.1085/jgp.95.3.397.
We have used the whole-cell patch-pipette technique to measure the step increases in the cell membrane capacitance (equivalent to the membrane area) caused by the fusion of secretory granules in degranulating murine mast cells. We have observed that up to 30% of the total membrane expansion caused by degranulation results from large fusion events that cannot be explained by the fusion of single secretory granules. These large events are observed mainly in the initial phase of a degranulation. We have developed a simple mathematical model for a mast cell to test whether these large events are caused by a stimulus-induced, granule-to-granule fusion that occurs before their exocytosis (multigranular exocytosis). Our results suggest that the large fusion events are caused by the exocytosis of granule aggregates that existed before stimulation and that are located at the cell's periphery. We propose a novel mechanism by which granule aggregates can be formed at the periphery of the cell. This mechanism relies on the ability of a transiently fused granule ("flicker") to fuse with more internally located granules in a sequential manner. This pattern may result in the formation of larger peripheral granules that later on can fuse with the membrane. The formation of peripheral granule aggregates may potentiate a subsequent secretory response.
我们运用全细胞膜片钳技术来测量脱颗粒小鼠肥大细胞中分泌颗粒融合所引起的细胞膜电容（等同于膜面积）的阶跃增加。我们观察到，脱颗粒引起的总膜扩张中，高达30%源于无法用单个分泌颗粒融合来解释的大型融合事件。这些大型事件主要在脱颗粒的初始阶段被观察到。我们为肥大细胞建立了一个简单的数学模型，以测试这些大型事件是否由刺激诱导的、在颗粒胞吐作用（多颗粒胞吐）之前发生的颗粒间融合所导致。我们的结果表明，大型融合事件是由刺激前就已存在且位于细胞周边的颗粒聚集体的胞吐作用引起的。我们提出了一种颗粒聚集体能够在细胞周边形成的新机制。该机制依赖于一个瞬时融合的颗粒（“闪烁”）以连续方式与更多位于内部的颗粒融合的能力。这种模式可能导致形成更大的周边颗粒，随后这些颗粒能够与细胞膜融合。周边颗粒聚集体的形成可能会增强后续的分泌反应。
