Secretory granules are recaptured largely intact after stimulated exocytosis in cultured endocrine cells.

J. W. Taraska, D. Perrais, M. Ohara-Imaizumi, S. Nagamatsu, W. Almers
Proceedings of the National Academy of Sciences. 2003-01-21; 100(4): 2070-2075
DOI: 10.1073/pnas.0337526100

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1. Proc Natl Acad Sci U S A. 2003 Feb 18;100(4):2070-5. Epub 2003 Jan 21.

Secretory granules are recaptured largely intact after stimulated exocytosis in
cultured endocrine cells.

Taraska JW(1), Perrais D, Ohara-Imaizumi M, Nagamatsu S, Almers W.

Author information:
(1)Vollum Institute, Oregon Health and Sciences University, 3181 SW Sam Jackson
Park Road, Portland, OR 97201, USA.

Comment in
Proc Natl Acad Sci U S A. 2003 Mar 4;100(5):2171-3.

Classical cell biology teaches that exocytosis causes the membrane of exocytic
vesicles to disperse into the cell surface and that a cell must later retrieve by
molecular sorting whatever membrane components it wishes to keep inside. We have
tested whether this view applies to secretory granules in intact PC-12 cells.
Three granule proteins were labeled with fluorescent proteins in different
colors, and two-color evanescent-field microscopy was used to view single
granules during and after exocytosis. Whereas neuro-peptide Y was lost from
granules in seconds, tissue plasminogen activator (tPA) and the membrane protein
phogrin remained at the granule site for over 1 min, thus providing markers for
postexocytic granules. When tPA was imaged simultaneously with cyan fluorescent
protein (CFP) as a cytosolic marker, the volume occupied by the granule appeared
as a dark spot where it excluded CFP. The spot remained even after tPA reported
exocytosis, indicating that granules failed to flatten into the cell surface.
Phogrin was labeled with GFP at its luminal end and used to sense the pH in
granules. When exocytosis caused the acidic granule interior to neutralize,
GFP-phogrin at first brightened and later dimmed again as the interior separated
from the extracellular space and reacidified. Reacidification and dimming could
be reversed by application of NH(4)Cl. We conclude that most granules reseal in

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