Mechanisms of Exocytosis

Abstract

Vesicles are cellular organelles, in which signaling molecules (neurotransmitters or hormones) are stored and are essential for the function of neurons and endocrine cells in supporting the communication between tissues and organs. Upon stimulation the signaling molecules stored inside vesicles are released from cells by exocytosis. This fundamental biological process consists of membrane fusion between the vesicles and the plasma membrane, leading to the formation of an aqueous channel – the fusion pore – through which signaling molecules exit into the extracellular space or blood stream. The vesicle cargo discharge initially requires the delivery of vesicles to the plasma membrane, where vesicles dock and get primed for fusion with the plasma membrane. Classical view holds that stimulation initiates the fusion pore formation and vesicle cargo discharge in an all-or-none fashion. Once formed the fusion pore may close (transient, “kiss-and-run” exocytosis) or expand, leading to the full collapse of the vesicle membrane into the plasma membrane (full fusion exocytosis). However, recent studies indicate that exocytosis may not be as simple. Here we highlight the novel findings which indicate that transient fusion pore is subject to regulations, which affect the release competence of a single vesicle. Our recent studies have shown that in pituitary lactotrophs vesicle release of peptide signaling molecules involves modulation of fusion pore kinetics and fusion pore conductance.

Keywords

• exocytosis
• vesicle
• fusion pore
• transient/full fusion
• pituitary lactotrophs
• peptide hormones