Department of Chemistry, Institute of Technology, University of Minnesota, Minneapolis, 55455, USA.
ACS Chem Biol. 2010 Sep 17;5(9):819-28. doi: 10.1021/cb100130b.
Exocytosis is a fundamental cellular process, pivotal in a wide range of cell types, used to deliver chemical messengers from one cell to another cell or tissue. While a tremendous amount of knowledge has been gained in the past several decades about the exocytotic machinery, recently it has become clear that the role of membrane lipids is also crucial in this process. In particular, the critical role of the abundant and ubiquitous cholesterol molecules has not been well-defined. Early insight has been gleaned from single cell amperometric studies on several commonly used secretory cell models, including chromaffin cells and PC12 cells; however, these secretory cell models are not ideal because manipulations of membrane cholesterol content may influence downstream cholesterol-dependent processes, making data interpretation difficult. Herein, blood platelets are employed as a simpler secretory cell model based on their anuclear nature and unique chemical messenger exocytosis behavior. Carbon-fiber microelectrochemistry was employed to measure real-time exocytosis from single platelets with depleted or enriched cholesterol either in the naturally occurring form or as the synthetic analogue epicholesterol. The experimental results show that membrane cholesterol directly modulates the secretion efficiency of individual platelets, as well as the kinetics of secretion events. Moreover, substitution of platelet membrane cholesterol with epicholesterol yields exocytotic behavior indistinguishable from that of normal platelets, arguing against the possibility of cholesterol-specific interactions in regulating exocytosis. It is clear from this work that membrane cholesterol plays a critical biophysical, rather than biochemical, role in platelet exocytosis and likely in exocytosis in general.
胞吐作用是一种基本的细胞过程，在广泛的细胞类型中都起着关键作用，用于将化学信使从一个细胞传递到另一个细胞或组织。尽管在过去几十年中，人们对胞吐作用机制已经有了大量的了解，但最近人们清楚地认识到，膜脂在这个过程中也起着至关重要的作用。特别是，丰富而普遍存在的胆固醇分子的关键作用尚未得到很好的定义。早期的认识是从对几种常用分泌细胞模型（包括嗜铬细胞和 PC12 细胞）的单细胞安培研究中获得的；然而，这些分泌细胞模型并不理想，因为膜胆固醇含量的操纵可能会影响下游依赖胆固醇的过程，使得数据解释变得困难。在此，血小板被用作一种更简单的分泌细胞模型，基于其无核性质和独特的化学信使胞吐作用行为。碳纤维微电化学被用来测量单个血小板实时的胞吐作用，这些血小板的胆固醇含量要么是自然存在的形式，要么是合成类似物表胆固醇。实验结果表明，膜胆固醇直接调节单个血小板的分泌效率，以及分泌事件的动力学。此外，用表胆固醇替代血小板膜胆固醇产生的胞吐作用与正常血小板的胞吐作用无法区分，这排除了胆固醇特异性相互作用在调节胞吐作用中的可能性。从这项工作中可以清楚地看出，膜胆固醇在血小板胞吐作用中起着至关重要的物理作用，而不是生化作用，而且可能在一般的胞吐作用中也是如此。
