Masedunskas Andrius, Porat-Shliom Natalie, Weigert Roberto
Commun Integr Biol. 2012 Jan 1;5(1):84-7. doi: 10.4161/cib.18258.
In all the major secretory organs regulated exocytosis is a fundamental process that is used for releasing molecules in the extracellular space. Molecules destined for secretion are packaged into secretory vesicles that fuse with the plasma membrane upon the appropriate stimulus. In exocrine glands, large secretory vesicles fuse with specialized domains of the plasma membrane, which form ductal structures that are in direct continuity with the external environment and exhibit various architectures and diameters. In a recent study, we used intravital microscopy to analyze in detail the dynamics of exocytic events in the salivary glands of live rodents under conditions that cannot be reproduced in in vitro or ex vivo model systems. We found that after the opening of the fusion pore large secretory vesicles gradually collapse with their limiting membranes being completely absorbed into the apical plasma membrane canaliculi within 40-60 sec. Moreover, we observed that this controlled collapse requires the contractile activity of actin and its motor myosin II, which are recruited onto the large secretory vesicles immediately after their fusion with the plasma membrane. Here we suggest that the actomyosin complex may be required to facilitate exocytosis in those systems, such as the salivary glands, in which the full collapse of the vesicles is not energetically favorable due to a difference in membrane tension between the large secretory vesicles and the canaliculi.
在所有受调节的主要分泌器官中，胞吐作用是一个基本过程，用于在细胞外空间释放分子。 destined for secretion are packaged into secretory vesicles that fuse with the plasma membrane upon the appropriate stimulus. 在外分泌腺中，大型分泌囊泡与质膜的特化区域融合，这些区域形成与外部环境直接连续的导管结构，并呈现出各种结构和直径。在最近的一项研究中，我们使用活体显微镜在体外或离体模型系统无法再现的条件下，详细分析了活啮齿动物唾液腺中胞吐事件的动态。我们发现，融合孔打开后，大型分泌囊泡逐渐塌陷，其限制膜在40-60秒内完全被吸收到顶端质膜微管中。此外，我们观察到这种受控的塌陷需要肌动蛋白及其运动肌球蛋白II的收缩活性，它们在与质膜融合后立即被招募到大型分泌囊泡上。在这里，我们认为肌动球蛋白复合物可能是那些系统（如唾液腺）中促进胞吐作用所必需的，在这些系统中，由于大型分泌囊泡和微管之间的膜张力差异，囊泡的完全塌陷在能量上是不利的。
