Amperometry recording reveals the exocytosis of catecholamine from individual vesicles as a sequential process, typically beginning slowly with a prespike foot, accelerating sharply to initiate a spike, reaching a peak, and then decaying. This complex sequence reflects the interplay between diffusion, flux through a fusion pore, and possibly dissociation from a vesicle's dense core. In an effort to evaluate the impacts of these factors, a model was developed that combines diffusion with flux through a static pore. This model accurately recapitulated the rapid phase of a spike but generated relations between spike shape parameters that differed from the relations observed experimentally. To explore the possible role of fusion pore dynamics, a transformation of amperometry current was introduced that yields fusion pore permeability divided by vesicle volume (g/V). Applying this transform to individual fusion events yielded a highly characteristic time course. g/V initially tracks the current, increasing ∼15-fold from the prespike foot to the spike peak. After the peak, g/V unexpectedly declines and settles into a plateau that indicates the presence of a stable postspike pore. g/V of the postspike pore varies greatly between events and has an average that is ∼3.5-fold below the peak value and ∼4.5-fold above the prespike value. The postspike pore persists and is stable for tens of milliseconds, as long as catecholamine flux can be detected. Applying the g/V transform to rare events with two peaks revealed a stepwise increase in g/V during the second peak. The g/V transform offers an interpretation of amperometric current in terms of fusion pore dynamics and provides a, to our knowledge, new frameworkfor analyzing the actions of proteins that alter spike shape. The stable postspike pore follows from predictions of lipid bilayer elasticity and offers an explanation for previous reports of prolonged hormone retention within fusing vesicles.

中文翻译：

---

内分泌细胞释放儿茶酚胺过程中的融合孔扩张和收缩

电流测量法记录显示，作为一个连续过程，从单个囊泡中排出儿茶酚胺是一个连续的过程，通常从预尖峰脚开始缓慢，急剧加速以启动尖峰，达到峰值，然后衰减。这种复杂的序列反映了扩散、通过融合孔的通量以及可能与囊泡致密核心的解离之间的相互作用。为了评估这些因素的影响，开发了一个模型，该模型将扩散与通过静态孔的通量相结合。该模型准确地概括了尖峰的快速阶段，但生成的尖峰形状参数之间的关系与实验观察到的关系不同。为了探索融合孔隙动力学的可能作用，引入了安培电流的转换，产生融合孔隙渗透率除以囊泡体积 (g/V)。将这种变换应用于单个融合事件产生了一个极具特征的时间过程。g/V 最初跟踪电流，从预尖峰脚到尖峰峰值增加约 15 倍。在峰值之后，g/V 出乎意料地下降并进入一个平台，表明存在稳定的后刺孔。峰值后孔的 g/V 在不同事件之间变化很大，平均值比峰值低约 3.5 倍，比峰值高约 4.5 倍。只要可以检测到儿茶酚胺通量，后刺孔就会持续存在并稳定数十毫秒。将 g/V 变换应用于具有两个峰的罕见事件显示在第二个峰期间 g/V 逐步增加。g/V 变换在融合孔动力学方面提供了安培电流的解释，并提供了一个新的框架，用于分析改变尖峰形状的蛋白质的作用。稳定的后刺孔遵循脂质双层弹性的预测，并为先前关于融合囊泡内激素滞留时间延长的报道提供了解释。