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. Author manuscript; available in PMC: 2015 Sep 23.
Published in final edited form as: Ultramicroscopy. 2009 Mar 28;109(8):1094–1104. doi: 10.1016/j.ultramic.2009.03.043

Figure 1.

Figure 1

Porosomes at the plasma membrane in pancreatic acinar cell and the nerve terminal. (A) AFM micrograph depicting ‘pits’ (yellow arrow) and ‘porosomes’ within (blue arrow), at the apical plasma membrane in a live pancreatic acinar cell. (B) To the right is a schematic drawing depicting porosomes at the cell plasma membrane (PM), where membrane-bound secretory vesicles called zymogen granules (ZG), dock and fuse to release intravesicular contents. (C) A high resolution AFM micrograph shows a single pit with four 100–180 nm porosomes within. (D) An electron micrograph depicting a porosome (red arrowhead) close to a microvilli (MV) at the apical plasma membrane (PM) of a pancreatic acinar cell. Note association of the porosome membrane (yellow arrowhead), and the zymogen granule membrane (ZGM) (red arrow head) of a docked ZG (inset). Cross section of a circular complex at the mouth of the porosome is seen (blue arrow head). (E) The bottom left panel shows an electron micrograph of a porosome (red arrowhead) at the nerve terminal, in association with a synaptic vesicle (SV) at the presynaptic membrane (Pre-SM). Notice a central plug at the neuronal porosome opening. (F) The bottom right panel is an AFM micrograph of a neuronal porosome in physiological buffer, also showing the central plug (red arrowhead) at its opening. It is believed that the central plug in neuronal porosomes may regulate its rapid close-open conformation during neurotransmitter release. The neuronal porosome is an order of magnitude smaller (10–15 nm) in comparison to porosome in the exocrine pancreas [17].