Fusion Pore Expansion Is a Slow, Discontinuous, and Ca2+-Dependent Process Regulating Secretion from Alveolar Type II Cells

In alveolar type II cells, the release of surfactant is considerably delayed after the formation of exocytotic fusion pores, suggesting that content dispersal may be limited by fusion pore diameter and subject to regulation at a postfusion level. To address this issue, we used confocal FRAP and N-(3...

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Bibliographic Details
Published in:The Journal of cell biology 2001-10, Vol.155 (2), p.279-289
Main Authors: Haller, Thomas, Dietl, Paul, Pfaller, Kristian, Frick, Manfred, Mair, Norbert, Paulmichl, Markus, Hess, Michael W., Fürst, Johannes, Maly, Karl
Format: Article
Language:English
Subjects:
Adenosine Triphosphate - pharmacology
Animals
Calcium
Calcium - physiology
Cells
Cells, Cultured
Cellular biology
Dyes
Epithelial cells
Exocytosis
Fluorescence
Fluorescent Dyes - chemistry
Fusion
Kinetics
Lungs
Membrane Fusion
Microscopy, Confocal
Microscopy, Electron, Scanning
Physiological regulation
Pulmonary alveoli
Pulmonary Alveoli - secretion
Pulmonary Alveoli - ultrastructure
Pulmonary Surfactants - secretion
Pyridinium Compounds - chemistry
Quaternary Ammonium Compounds - chemistry
Rats
Rats, Sprague-Dawley
Regulation
Reproducibility of Results
Secretion
Secretory Vesicles - ultrastructure
Surfactants
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Summary:In alveolar type II cells, the release of surfactant is considerably delayed after the formation of exocytotic fusion pores, suggesting that content dispersal may be limited by fusion pore diameter and subject to regulation at a postfusion level. To address this issue, we used confocal FRAP and N-(3-triethylammoniumpropyl)-4-(4-[dibutylamino]styryl) pyridinium dibromide (FM 1-43), a dye yielding intense localized fluorescence of surfactant when entering the vesicle lumen through the fusion pore (Haller, T., J. Ortmayr, F. Friedrich, H. Volkl, and P. Dietl. 1998. Proc. Natl. Acad. Sci. USA. 95:1579-1584). Thus, we have been able to monitor the dynamics of individual fusion pores up to hours in intact cells, and to calculate pore diameters using a diffusion model derived from Fick's law. After formation, fusion pores were arrested in a state impeding the release of vesicle contents, and expanded at irregular times thereafter. The expansion rate of initial pores and the probability of late expansions were increased by elevation of the cytoplasmic Ca2+concentration. Consistently, content release correlated with the occurrence of Ca2+oscillations in ATP-treated cells, and expanded fusion pores were detectable by EM. This study supports a new concept in exocytosis, implicating fusion pores in the regulation of content release for extended periods after initial formation.
ISSN:0021-9525
1540-8140
DOI:10.1083/jcb.200102106