Fusion-Activated Ca2+ Entry: An “Active Zone” of Elevated Ca2+ during the Postfusion Stage of Lamellar Body Exocytosis in Rat Type II Pneumocytes

Miklavc, P, Frick, M, Wittekindt, OH, Haller, T and Dietl, P 2010, 'Fusion-Activated Ca2+ Entry: An “Active Zone” of Elevated Ca2+ during the Postfusion Stage of Lamellar Body Exocytosis in Rat Type II Pneumocytes' , PLoS ONE, 5 (6) , e10982.

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Abstract

Background Ca2+ is essential for vesicle fusion with the plasma membrane in virtually all types of regulated exocytoses. However, in contrast to the well-known effects of a high cytoplasmic Ca2+ concentration ([Ca2+]c) in the prefusion phase, the occurrence and significance of Ca2+ signals in the postfusion phase have not been described before. Methodology/Principal Findings We studied isolated rat alveolar type II cells using previously developed imaging techniques. These cells release pulmonary surfactant, a complex of lipids and proteins, from secretory vesicles (lamellar bodies) in an exceptionally slow, Ca2+- and actin-dependent process. Measurements of fusion pore formation by darkfield scattered light intensity decrease or FM 1-43 fluorescence intensity increase were combined with analysis of [Ca2+]c by ratiometric Fura-2 or Fluo-4 fluorescence measurements. We found that the majority of single lamellar body fusion events were followed by a transient (t1/2 of decay = 3.2 s) rise of localized [Ca2+]c originating at the site of lamellar body fusion. [Ca2+]c increase followed with a delay of ∼0.2–0.5 s (method-dependent) and in the majority of cases this signal propagated throughout the cell (at ∼10 µm/s). Removal of Ca2+ from, or addition of Ni2+ to the extracellular solution, strongly inhibited these [Ca2+]c transients, whereas Ca2+ store depletion with thapsigargin had no effect. Actin-GFP fluorescence around fused LBs increased several seconds after the rise of [Ca2+]c. Both effects were reduced by the non-specific Ca2+ channel blocker SKF96365. Conclusions/Significance Fusion-activated Ca2+ entry (FACE) is a new mechanism that leads to [Ca2+]c transients at the site of vesicle fusion. Substantial evidence from this and previous studies indicates that fusion-activated Ca2+ entry enhances localized surfactant release from type II cells, but it may also play a role for compensatory endocytosis and other cellular functions.

Item Type: Article
Schools: Schools > School of Environment and Life Sciences
Journal or Publication Title: PLoS ONE
Publisher: Public Library of Science
ISSN: 1932-6203
Funders: Austrian Science Fund (FWF) grants P15742, P15743, and P20472, Deutsche Forschungsgemeinschaft (DFG) grant D1402, Marie Curie Research Training Network of the European Union
Depositing User: P Miklavc
Date Deposited: 24 Oct 2016 14:12
Last Modified: 09 Aug 2017 02:36
URI: http://usir.salford.ac.uk/id/eprint/40263

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