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J Cell Physiol. 2016 Jul;231(7):1593-600. doi: 10.1002/jcp.25256. Epub 2015 Dec 10.

Fusion Pore Size Limits 5-HT Release From Single Enterochromaffin Cell Vesicles.

Author information

1
Department of Human Physiology and Centre for Neuroscience, Flinders University, Adelaide, Australia.
2
Department of Anatomy and Histology and Centre for Neuroscience, Flinders University, Adelaide, Australia.
3
Discipline of Medicine, University of Adelaide, Adelaide, Australia.
4
South Australian Health and Medical Research Institute, Adelaide, Australia.

Abstract

Enterochromaffin cells are the major site of serotonin (5-HT) synthesis and secretion providing ∼95% of the body's total 5-HT. 5-HT can act as a neurotransmitter or hormone and has several important endocrine and paracrine roles. We have previously demonstrated that EC cells release small amounts of 5-HT per exocytosis event compared to other endocrine cells. We utilized a recently developed method to purify EC cells to demonstrate the mechanisms underlying 5-HT packaging and release. Using the fluorescent probe FFN511, we demonstrate that EC cells express VMAT and that VMAT plays a functional role in 5-HT loading into vesicles. Carbon fiber amperometry studies illustrate that the amount of 5-HT released per exocytosis event from EC cells is dependent on both VMAT and the H(+)-ATPase pump, as demonstrated with reserpine or bafilomycin, respectively. We also demonstrate that increasing the amount of 5-HT loaded into EC cell vesicles does not result in an increase in quantal release. As this indicates that fusion pore size may be a limiting factor involved, we compared pore diameter in EC and chromaffin cells by assessing the vesicle capture of different-sized fluorescent probes to measure the extent of fusion pore dilation. This identified that EC cells have a reduced fusion pore expansion that does not exceed 9 nm in diameter. These results demonstrate that the small amounts of 5-HT released per fusion event in EC cells can be explained by a smaller fusion pore that limits 5-HT release capacity from individual vesicles.

PMID:
26574734
DOI:
10.1002/jcp.25256
[Indexed for MEDLINE]

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