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（ACh, 500nM）诱导DELTAC和DELTAG同时升高。相反，低浓度（50nM）乙酰胆碱只诱导deltac -升高，而不诱导DELTAG。肝素内灌注消除了这些反应。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，要么单独启动胞吐。相比之下，低浓度的A23187选择性激活离子通道，而高浓度的A23187同时激活胞吐和离子通道。这些选择性反应模式的DELTAC和DELTAG取决于激动剂的选择和内部EGTA浓度。由此，我们对肌源性乙酰胆碱刺激对胞吐的选择性作用提出了两种可能的解释。首先，更多的高[Ca^<2+>] i区域，在空间上靠近分泌颗粒，激活胞外分泌。其次，一种未知的信号因子使胞外器的Ca^<2+>-亲和力增敏。采用相敏电容测量方法，对膜电容变化的时间过程进行了监测。在局部斑块-膜水平上，这些变化是随机发生的，可以解释为可逆的囊泡形成（膜转化）。步骤的大小分布采用负指数曲线拟合，表明膜转化能量似乎只有一个能量峰。在全内质网水平上增加腔内Ca^<2+>-浓度，膜电容增加。这表明囊泡可逆地转化为帽状，囊泡内部与内质网腔之间有连接。结果提示内质网腔Ca^<2+>参与了囊泡运输。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