Vacuolar sequential exocytosis of large dense-core vesicles in adrenal medulla.
Individual exocytic events in intact adrenal medulla were visualized by two-photon extracellular polar-tracer imaging. Exocytosis of chromaffin vesicles often occurred in a sequential manner, involving first vesicles located at the cell periphery and then those present deeper within the cytoplasm. Sequential exocytosis occurred preferentially at regions of the plasma membrane facing the intercellular space. The compound vesicles swelled to more than five times their original volume and formed vacuolar exocytic lumens as a result of expansion of intravesicular gels and their confinement within the lumen by the fusion pore and the narrow intercellular space. Such luminal swelling greatly promoted sequential exocytosis. The SNARE protein SNAP25 rapidly migrated from the plasma membrane to the membrane of fused vesicles. These data indicate that vesicles present deeper within the cytoplasm can be fusion ready like those at the cell periphery, and that swelling of exocytic lumens promotes assembly of the fusion machinery. We suggest the existence of two molecular configurations for fusion-ready states in Ca2+ -dependent exocytosis.
Division of Biophysics, Center for Disease Biology and Integrative Medicine, Faculty of Medicine, University of Tokyo, Hongo, Tokyo, Japan.
Takuya
T
Kishimoto
Ryoichi
R
Kimura
Ting-Ting
TT
Liu
Tomomi
T
Nemoto
Noriko
N
Takahashi
Haruo
H
Kasai
D000313:Adrenal Medulla / Q000166:cytology / Q000502:physiology*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D002417:Cattle; D002462:Cell Membrane / Q000378:metabolism*; D019439:Chromaffin Cells / Q000166:cytology / Q000502:physiology*; D005089:Exocytosis / Q000502:physiology*; D018613:Microscopy, Confocal; D021381:Protein Transport / Q000502:physiology; D051381:Rats; D050825:Synaptosomal-Associated Protein 25 / Q000378:metabolism*; D014617:Vacuoles / Q000502:physiology*
D050825:Synaptosomal-Associated Protein 25; D002118:Calcium