Unidad de Farmacología, Facultad de Medicina, Universidad de La Laguna, Tenerife, Spain.
Cell Calcium. 2012 Mar-Apr;51(3-4):338-41. doi: 10.1016/j.ceca.2011.12.009. Epub 2012 Jan 4.
Secretory vesicles of chromaffin cells are acidic organelles that maintain an increasing pH gradient towards the cytosol (5.5 vs. 7.3) that is mediated by V-ATPase activity. This gradient is primarily responsible for the accumulation of large concentrations of amines and Ca(2+), although the mechanisms mediating Ca(2+) uptake and release from granules, and the physiological relevance of these processes, remain unclear. The presence of a vesicular matrix appears to create a bi-compartmentalised medium in which the major fractions of solutes, including catecholamines, nucleotides and Ca(2+), are strongly associated with vesicle proteins, particularly chromogranins. This association appears to be favoured at acidic pH values. It has been demonstrated that disrupting the pH gradient of secretory vesicles reduces their rate of exocytosis and promotes the leakage of vesicular amines and Ca(2+), dramatically increasing the movement of secretory vesicles and triggering exocytosis. In this short review, we will discuss the data available that highlights the importance of pH in regulating the association between chromogranins, vesicular amines and Ca(2+). We will also address the potential role of vesicular Ca(2+) in two major processes in secretory cells, vesicle movement and exocytosis.
嗜铬细胞的分泌小泡是酸性细胞器，它们通过 V-ATPase 活性维持朝着细胞质（5.5 与 7.3）不断增加的 pH 梯度。尽管介导 Ca(2+)从颗粒摄取和释放的机制以及这些过程的生理相关性仍不清楚，但这种梯度主要负责胺和 Ca(2+)的大量积累。囊泡基质的存在似乎创造了一个双分隔的介质，其中溶质的主要部分，包括儿茶酚胺、核苷酸和 Ca(2+)，与囊泡蛋白，特别是 chromogranins 强烈相关。这种关联似乎在酸性 pH 值下更为有利。已经证明，破坏分泌小泡的 pH 梯度会降低其胞吐作用的速率，并促进囊泡胺和 Ca(2+)的渗漏，这极大地增加了分泌小泡的运动并触发胞吐作用。在这篇简短的综述中，我们将讨论强调 pH 在调节 chromogranins、囊泡胺和 Ca(2+)之间的关联中的重要性的现有数据。我们还将讨论囊泡 Ca(2+)在分泌细胞中的两个主要过程，即囊泡运动和胞吐作用中的潜在作用。
