Fusion-activated Ca 2+ entry via vesicular P2X 4 receptors promotes fusion pore opening and exocytotic content release in pneumocytes
- 15 August 2011
- journal article
- Published by Proceedings of the National Academy of Sciences in Proceedings of the National Academy of Sciences
- Vol. 108 (35), 14503-14508
- https://doi.org/10.1073/pnas.1101039108
Abstract
Ca(2+) is considered a key element in multiple steps during regulated exocytosis. During the postfusion phase, an elevated cytoplasmic Ca(2+) concentration ([Ca(2+)])(c) leads to fusion pore dilation. In neurons and neuroendocrine cells, this results from activation of voltage-gated Ca(2+) channels in the plasma membrane. However, these channels are activated in the prefusion stage, and little is known about Ca(2+) entry mechanisms during the postfusion stage. This may be particularly important for slow and nonexcitable secretory cells. We recently described a "fusion-activated" Ca(2+) entry (FACE) mechanism in alveolar type II (ATII) epithelial cells. FACE follows initial fusion pore opening with a delay of 200-500 ms. The site, molecular mechanisms, and functions of this mechanism remain unknown, however. Here we show that vesicle-associated Ca(2+) channels mediate FACE. Using RT-PCR, Western blot analysis, and immunofluorescence, we demonstrate that P2X(4) receptors are expressed on exocytotic vesicles known as lamellar bodies (LBs). Electrophysiological, pharmacological, and genetic data confirm that FACE is mediated via these vesicular P2X(4) receptors. Furthermore, analysis of fluorophore diffusion into and out of individual vesicles after exocytotic fusion provides evidence that FACE regulates postfusion events of LB exocytosis via P2X(4). Fusion pore dilation was clearly correlated with the amplitude of FACE, and content release from fused LBs was accelerated in fusions followed by FACE. Based on these findings, we propose a model for regulation of the exocytotic postfusion phase in nonexcitable cells in which Ca(2+) influx via vesicular Ca(2+) channels regulates fusion pore expansion and vesicle content release.Keywords
This publication has 58 references indexed in Scilit:
- Push-and-pull regulation of the fusion pore by synaptotagmin-7Proceedings of the National Academy of Sciences, 2010
- Fusion-Activated Ca2+ Entry: An “Active Zone” of Elevated Ca2+ during the Postfusion Stage of Lamellar Body Exocytosis in Rat Type II PneumocytesPLOS ONE, 2010
- Membrane compartments and purinergic signalling: occurrence and function of P2X receptors in lungThe FEBS Journal, 2008
- Emerging Roles of Presynaptic Proteins in Ca ++ -Triggered ExocytosisScience, 2002
- Biogenesis of lamellar bodies, lysosome-related organelles involved in storage and secretion of pulmonary surfactantSeminars in Cell & Developmental Biology, 2002
- Stretch stimulation: its effects on alveolar type II cell function in the lungComparative Biochemistry and Physiology Part A: Molecular & Integrative Physiology, 2001
- Exocytotic Insertion of Calcium Channels Constrains Compensatory Endocytosis to Sites of ExocytosisThe Journal of cell biology, 2000
- Fusion pore expansion in horse eosinophils is modulated by Ca2+ and protein kinase C via distinct mechanismsThe EMBO Journal, 1998
- A novel Ca2+‐dependent step in exocytosis subsequent to vesicle fusionFEBS Letters, 1995
- Peptide secretion: what do we know?The FASEB Journal, 1994