exocytóze

Exocytóze, also known as exocytose or exocitose in some languages, is a fundamental cellular process in which secretory vesicles fuse with the plasma membrane to release their contents outside the cell or to embed membrane components into the cell surface. Most exocytosis begins with vesicles budding from the Golgi apparatus or from endosomes, followed by trafficking along cytoskeletal tracks to the plasma membrane. Upon arrival, vesicles are docked and primed for fusion, a step regulated by a core set of proteins known as SNAREs. The vesicle-associated SNARE (v-SNARE, for example VAMP/synaptobrevin) forms a complex with target-SNAREs on the plasma membrane (such as syntaxin and SNAP-25), bringing membranes into close proximity. Fusion is tightly regulated by accessory proteins, including Munc18, complexin, and the Ca2+ sensor synaptotagmin, which couples calcium influx to membrane fusion in regulated exocytosis.

Exocytosis occurs in two main modes. Constitutive exocytosis is a continuous, unregulated process that delivers membrane proteins and lipids and supports membrane turnover. Regulated exocytosis is triggered by stimuli such as neural activity or hormones, leading to rapid release of secretory cargo (e.g., neurotransmitters, hormones, enzymes).

Functions include secretion, provision of extracellular signaling molecules, and expansion of the plasma membrane. Disruptions to exocytosis are linked to various diseases, including diabetes, neurodegenerative disorders, and immune dysfunction. Understanding exocytosis relies on studies of vesicle trafficking, SNARE biology, and calcium signaling.