Membrane fusion involves the merging of two phospholipid bilayers in an aqueous environment and is involved in many cellular processes, such as cell exocytosis. Synaptic vesicles are nanometer-sized organelles, which are packaged with chemical messengers (e.g., neurotransmitters, neurohormones, and neuropeptides). Each presynaptic nerve terminal contains hundreds of synaptic vesicles. When an action potential depolarizes the presynaptic plasma membrane, Ca2+ channels open, and Ca2+ flows into the nerve terminal to trigger the exocytosis of synaptic vesicles, thereby vesicles migrate to the plasma membrane of a cell, fuse, and release their contents into the extracellular space. These messengers can then bind to receptors on a target cell, thus inducing a cascade of signaling events in a complex network (Figure 14.1). Until now, several types of neurotransmitters, such as amino acids, monoamines, and peptides, have been found, but their function in the brain is not always clear. Exocytotic events occur on a millisecond timescale with transmitter release proportions varying from zepto- to femtomole amounts per vesicle, making them experimentally challenging to monitor. Several different kinds of bioanalytical techniques have been developed to measure chemical messengers in the extracellular fluid following exocytosis from tissue in vivo and to measure individual exocytotic events at single cells under in vitro experimental conditions with biological or artificial models.
All Science Journal Classification (ASJC) codes
- Chemical Engineering(all)
- Materials Science(all)