Journal of Cell Signaling
Open Access

A Short Note on Porosomes

Bhanu. P Jena^{* *}Correspondence: Dr. Bhanu. P Jena, Department of Physiology, Wayne State University School of Medicine, Detroit, USA, Email:

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Description

Porosomes are cup-shaped supra-molecular structures in eukaryotic cell membranes where secretory vesicles attach transiently during the fusion and secretion process. The creation of a fusion pore or continuity for the release of intra-vesicular contents from the cell is caused by the brief fusing of secretory vesicle membrane at the porosome base via SNARE proteins. The fusion hole created at the base of the porosome is briefly shut when secretion is completed. Porosomes are nanometersized vesicles that contain a variety of proteins, including chloride and calcium channels, actin, and SNARE proteins, which facilitate vesicle docking and fusion with the cell membrane. The vesicles swell after docking with the SNARE proteins, increasing their internal pressure. They then transiently fuse at the porosome's base, and the cell's pressured contents are expelled. Using electron microscopy to examine cells after secretion, it was discovered that there were more partially empty vesicles present. This suggests that only a fraction of the vesicular contents can leave the cell during the secretory phase. The size of porosomes varies depending on the cell type. Porosomes that are in the exocrine pancreas, endocrine, and neuroendocrine cells varies in diameter of 100 nm to 180 nm, while neurons varies in diameter of 10 nm to 15 nm about 1/10 the size of pancreatic porosome. Actin normally opens and closes porosomes, but because neurons require a quick response, they include central plugs that open to release contents and close to stop the release and the composition of the central plug. Porosomes have been shown to be the cell's global secretory apparatus. The neuronal porosome proteome has been broke down, revealing the machinery's molecular architecture and entire composition.

Actin normally opens and closes porosomes, but because neurons require a quick response, they include central plugs that open to release contents and close to stop the release and the composition of the central plug. Porosomes have been shown to be the cell's global secretory apparatus. The neuronal porosome proteome has been broke down, revealing the machinery's molecular architecture and entire composition. The porosome structure would be entirely demolished if secretory vesicles completely merged at the cell plasma membrane, and the production of partly empty vesicles following cell secretion would be unexplainable. The formation of partially empty vesicles following cell secretion may now be explained thanks to the discovery of the porosome and the temporary docking, fusion, and dissociation of secretory vesicles at its base. Several studies from a variety of labs agree that "secretory granules are recaptured largely intact after stimulated exocytosis in cultured endocrine cells," that "single synaptic vesicles fuse transiently and successively without loss of identity," that "Zymogen granule exocytosis is characterized by long fusion pore openings and preservation of vesicle lipid identity," and that the "count of growth harmones in secretory vesicles."

Porosomes are specialized plasma membrane structures found in all secretory cells, including exocrine, endocrine, neuroendocrine, and neuronal cells. Because Porosomes in exocrine and neuroendocrine cells measure 100–180 nm and only a 20–35 percent increase in porosome diameter is observed after attaching and binding of 0.2–1.2 m diameter secretory vesicles, it is concluded that secretory vesicles "transiently" dock and fuse at the porosome complex's base to release their contents to the outside. In contrary to popular assumption, secretory vesicles in mammalian cells completely merge at the cell plasma membrane, resulting in passive diffusion of vesicular contents to the cell exterior and subsequent endocytosis retrieval of the surplus membrane at a later period.