Exocytosis means transport from inside of the cell to extracellular space. For exocytosis, the secretory vesicles inside the cell fuses with the plasma membrane and the contents of the vesicles are released outside the cell. Exocytosis is of two types: a. constitutive i.e. exocytosis performed by all cells, and b. regulated i.e., exocytosis performed by cells such as neurons and cells of endocrine and exocrine glands.
Exocytosis is triggered by various factors. Regulated exocytosis is regulated by calcium ions. Many calcium ion binding proteins are involved in exocytosis. The level of calcium ions inside the cells regulate the calcium ion binding proteins which in turn regulate the process of exocytosis. In nerve cell synapses, synaptotagmin is essential for exocytosis. GTP-binding proteins are involved in both constitutive and regulated exocytosis. Another protein, SNARE mediate vesicle fusion into the cell membrane.
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