Using a Cell Model to Study the Effect of Cholesterol on Exocytosis

Exocytosis is an essential cellular process in neuronal communication. This cellular function involves vesicle fusion and vesicle content release of neurotransmitter molecules. In the quest to determine the molecules affecting exocytosis, simplified model systems such as artificial cells are valuable tools. The models allow us to study the effect of different components such as various lipids on the process of exocytosis in a controlled manner. In this study the effect of cholesterol on membrane dynamics for exocytosis has been investigated. Membrane lipids including cholesterol provide a platform for carrying out and regulating exocytosis. Although cholesterol is a major component of membrane and certainly affects exocytosis, the overall biochemical and biophysical properties are not been fully understood.Two different artificial cell models have been applied in this work. The first cell model is based on pure lipid composition that provides total control of all the components in the system. The second cell model is constructed from cell plasma membrane from PC12 cells. This model gives the advantage of working with a system that is very much like a real cell and has almost all the components of the cell membrane including membrane proteins.Kinetic information of single vesicle release of dopamine is recorded using carbon fiber amperometry in both models. In the former model we have shown that adding cholesterol to the system slows the kinetics of the release in a concentration dependent manner. In the latter model, we show that depleting cholesterol from the membrane enhances the kinetics of the events. The result from the latter model not only validates the result from pure lipid-liposome system but also indicates the importance of lipids in the presence of all the membrane components including proteins.