Fusion Pores as Regulators of Quantal Size and Cellular Physiology

The timely release of chemical messengers is a crucial step in cell-to-cell communication. Does this release occur as a passive diffusion from the donor membrane or it is actively regulated? A series of studies indicated that chemical messengers' secretion is "sub-quantal". This mode of secretion demands a strongly regulated release mechanism and calls for a thorough characterization of the release sites. When secretory vesicles fuse with the plasma membrane, ephemeral fusion pores serve as the first aqueous connection between the lumen of secretory vesicle and the cell exterior through which chemical messengers are released. Here, we discuss the molecular players that directly regulate fusion pore properties. This has consequences in controlling the amount of chemical messengers' secretion, hence controlling the quantal size. A thorough understanding of the role of regulatory factors in controlling quantal size can help design potent therapeutics to alter vesicular secretion under pathological conditions.