Features of granule motion and of vesicular fusion by local cell signaling

我们监测了毒蕈碱乙酰胆碱刺激单个大鼠胰腺腺泡细胞引起的膜电容（DELTAC）和电导（DELTAG）的变化。乙酰胆碱（Acetylcholine，500 nM）诱导DELTAC和DELTAG同时增加，而低浓度ACh（50 nM）只诱导DELTAC增加，而不诱导DELTAG增加，这些反应可被肝素内灌注所消除。这表明肌醇1，4，5-三磷酸介导的内部Ca^2+动员要么同时激活胞吐和离子通道，要么只启动胞吐。相比之下，低浓度的A23187选择性激活离子通道，但高浓度的胞吐作用和离子通道同时激活。DELTAC和DELTAG的这些选择性反应模式取决于激动剂的选择和内部EGTA浓度。从这一点，我们假设两个可能的解释毒蕈碱乙酰胆碱刺激的选择性作用的胞吐。一是 ...更多信息 高[Ca^<2+>] i区，空间上靠近分泌颗粒，激活胞吐作用。第二，一种未知的信号传导因子使胞吐器的Ca^2+亲和力敏感。将相敏电容测量应用于ER制备，监测膜电容变化的时间过程。在局部膜片膜水平上，这些变化以离散的开和关步骤随机发生，这可以解释为可逆的囊泡形成（膜转化）。台阶的大小分布符合负指数曲线，表明膜转化能似乎有一个单一的能量峰。在整个内质网水平上，随着囊泡内腔Ca^<2+>-浓度的增加，膜电容增加，这表明囊泡可逆地转变为帽状结构，囊泡内部与内质网内腔连接。提示内质网内Ca^<2+>参与了囊泡的转运.少

We have monitored changes in membrane capacitance (DELTAC) and conductance (DELTAG) induced by muscarinic acetylcholine stimulation in single rat pancreatic acinar cells. Acetylcholine (ACh, 500nM) induced simultaneous increases of DELTAC and DELTAG.In contrast, a low concentration (50nM) of ACh exclusively induced DELTAC-increases without DELTAG.These reponses were abolished by the internal perfusion of heparin. It indicates that inositol 1,4,5-trisphosphate-mediated internal Ca^<2+>-mobilization either simultaneously activates exocytosis and ion channels or exclusively initiates exocytosis. In comparison, a low concentration of A23187 selectively activated ion channels but a high concentration exocytosis and ion channels simultaneously. These selective response patterns of DELTAC and DELTAG depend on the choice of agonist and the internal EGTA concentration. From this, we postulated two possible explanation for the selective action of muscarnic ACh stimulation on exocytosis. First, a … More n area of high [Ca^<2+>] i, spatially close to secretory granules, activates exocytosis. Second, an as yet unknown signalling factor sensitizes the Ca^<2+>-affinity of the exocytotic apparatus. Applying a phase-sensitive capacitance measurement to the ER preparation, the time course of the changes in membrane capacitance were monitored. At the local patch-membrane level, the changes occurred at random as discrete on-and off-steps, which can be interpreted as reversible vesicle formation (membrane transformation). The size distribution of the steps were fitted by a negative exponential curve, suggesting the membrane transformation energy seems to have a single energy peak. Increasing the lumenal Ca^<2+>-concentration at the whole-ER level, a rise in the membrane capacitance was found. This indicates that the vesicles are reversibly transformed to caps with a connection between the vesicle interior and the ER lumen. The result suggests the involvement of the ER lumenal Ca^<2+> in the vesicular transport. Less