Two Distinct Modes of Exocytotic Fusion Pore Expansion in Large Astrocytic Vesicles |
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Authors: | Hong Peng Ning Kang Jun Xu Patric K Stanton Jian Kang |
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Institution: | From the ‡Department of Cell Biology and Anatomy, New York Medical College, Valhalla, New York 10595 and ;the §East Hospital, Tongji University School of Medicine, Shanghai 200120, China |
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Abstract: | Formation of the fusion pore is a central question for regulated exocytosis by which secretory cells release neurotransmitters or hormones. Here, by dynamically monitoring exocytosis of large vesicles (2–7 μm) in astrocytes with two-photon microscopy imaging, we found that the exocytotic fusion pore was generated from the SNARE-dependent fusion at a ring shape of the docked plasma-vesicular membrane and the movement of a fusion-produced membrane fragment. We observed two modes of fragment movements, 1) a shift fragment that shifted to expand the fusion pore and 2) a fall-in fragment that fell into the collapsed vesicle to expand the fusion pore. Shift and fall-in modes are associated with full and partial collapses of large vesicles, respectively. The astrocytic marker, sulforhodamine 101, stained the fusion-produced membrane fragment more brightly than FM 1-43. Sulforhodamine 101 imaging showed that double fusion pores could simultaneously occur in a single vesicle (16% of large vesicles) to accelerate discharge of vesicular contents. Electron microscopy of large astrocytic vesicles showed shift and fall-in membrane fragments. Two modes of fusion pore formation demonstrate a novel mechanism underlying fusion pore expansion and provide a new explanation for full and partial collapses of large secretory vesicles. |
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Keywords: | Astrocytes Exocytosis Fluorescence Membrane Fusion Vesicles Pore Expansion |
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