Blank P S, Cho M S, Vogel S S, Kaplan D, Kang A, Malley J, Zimmerberg J
Laboratory of Cellular and Molecular Biophysics, National Institute of Child Health and Human Development, Bethesda, Maryland 20892, USA.
J Gen Physiol. 1998 Nov;112(5):559-67. doi: 10.1085/jgp.112.5.559.
A graded response to calcium is the defining feature of calcium-regulated exocytosis. That is, there exist calcium concentrations that elicit submaximal exocytotic responses in which only a fraction of the available population of secretory vesicles fuse. The role of calcium-dependent inactivation in defining the calcium sensitivity of sea urchin egg secretory vesicle exocytosis in vitro was examined. The cessation of fusion in the continued presence of calcium was not due to calcium-dependent inactivation. Rather, the calcium sensitivity of individual vesicles within a population of exocytotic vesicles is heterogeneous. Any specific calcium concentration above threshold triggered subpopulations of vesicles to fuse and the size of the subpopulations was dependent upon the magnitude of the calcium stimulus. The existence of multiple, stable subpopulations of vesicles is consistent with a fusion process that requires the action of an even greater number of calcium ions than the numbers suggested by models based on the assumption of a homogeneous vesicle population.
对钙的分级反应是钙调节性胞吐作用的决定性特征。也就是说，存在一些钙浓度会引发次最大胞吐反应，其中只有一部分可用的分泌囊泡群体发生融合。研究了钙依赖性失活在体外定义海胆卵分泌囊泡胞吐作用的钙敏感性方面的作用。在持续存在钙的情况下融合的停止并非由于钙依赖性失活。相反，一群胞吐囊泡中单个囊泡的钙敏感性是异质的。任何高于阈值的特定钙浓度都会触发囊泡亚群融合，且亚群的大小取决于钙刺激的强度。囊泡存在多个稳定亚群这一现象与融合过程相一致，该过程所需的钙离子数量比基于均匀囊泡群体假设的模型所暗示的数量还要多。
