Recapture after exocytosis causes differential retention of protein in granules of bovine chromaffin cells.
The Journal of Physiology. 2004-10-01; 560(2): 413-428
DOI: 10.1113/jphysiol.2004.064410
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1. J Physiol. 2004 Oct 15;560(Pt 2):413-28. Epub 2004 Aug 5.
Recapture after exocytosis causes differential retention of protein in granules
of bovine chromaffin cells.
Perrais D(1), Kleppe IC, Taraska JW, Almers W.
Author information:
(1)Vollum Institute, Oregon Health & Science University, 3181 SW Sam Jackson Park
Road, Portland, OR 97239-3098, USA.
After exocytosis, chromaffin granules release essentially all their
catecholamines in small fractions of a second, but it is unknown how fast they
release stored peptides and proteins. Here we compare the exocytic release of
fluorescently labelled neuropeptide Y (NPY) and tissue plasminogen activator from
single granules. Exocytosis was tracked by measuring the membrane capacitance,
and single granules in live cells were imaged by evanescent field microscopy.
Neuropeptide Y left most granules in small fractions of a second, while tissue
plasminogen activator remained in open granules for minutes. Taking advantage of
the dependence on pH of the fluorescence of green fluorescent protein, we used
rhythmic external acidification to determine whether and when granules re-sealed.
One-third of them re-sealed within 100 s and retained significant levels of
tissue plasminogen activator. Re-sealing accounts for only a fraction of the
endocytosis monitored in capacitance measurements. When external [Ca2+] was
raised, even neuropeptide Y remained in open granules until they re-sealed. It is
concluded that a significant fraction of chromaffin granules re-seal after
exocytosis, and retain those proteins that leave granules slowly. We suggest that
granules vary the stoichiometry of release by varying both granule re-sealing and
the association of proteins with the granule matrix.
DOI: 10.1113/jphysiol.2004.064410
PMCID: PMC1665250
PMID: 15297569 [Indexed for MEDLINE]