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

• DOI: 10.1371/journal.pone.0010982
• Publication Date: 2010-06-08T20:00:06Z
• Authors: Pika Miklavc; Manfred Frick; Oliver H. Wittekindt; Thomas Haller; Paul Dietl
• Keywords: Lamellar granule; Thapsigargin

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