title: Fusion-activated cation entry (FACE) via P2X₄ couples surfactant secretion and alveolar fluid transport.
abstract: Two fundamental mechanisms within alveoli are essential for lung function: regulated fluid transport and secretion of surfactant. Surfactant is secreted via exocytosis of lamellar bodies (LBs) in alveolar type II (ATII) cells. We recently reported that LB exocytosis results in fusion-activated cation entry (FACE) via P2X₄ receptors on LBs. We propose that FACE, in addition to facilitating surfactant secretion, modulates alveolar fluid transport. Correlative fluorescence and atomic force microscopy revealed that FACE-dependent water influx correlated with individual fusion events in rat primary ATII cells. Moreover, ATII cell monolayers grown at air-liquid interface exhibited increases in short-circuit current (Isc) on stimulation with ATP or UTP. Both are potent agonists for LB exocytosis, but only ATP activates FACE. ATP, not UTP, elicited additional fusion-dependent increases in Isc. Overexpressing dominant-negative P2X₄ abrogated this effect by ∼50%, whereas potentiating P2X4 lead to ∼80% increase in Isc. Finally, we monitored changes in alveolar surface liquid (ASL) on ATII monolayers by confocal microscopy. Only stimulation with ATP, not UTP, led to a significant, fusion-dependent, 20% decrease in ASL, indicating apical-to-basolateral fluid transport across ATII monolayers. Our data support the first direct link between LB exocytosis, regulation of surfactant secretion, and transalveolar fluid resorption via FACE.
authors: Institute of General Physiology, University of Ulm, Ulm, Germany.
authors: Kristin E
authors: KE
authors: Thompson
authors: Jonas P
authors: JP
authors: Korbmacher
authors: Elena
authors: E
authors: Hecht
authors: Nina
authors: N
authors: Hobi
authors: Oliver H
authors: OH
authors: Wittekindt
authors: Paul
authors: P
authors: Dietl
authors: Christine
authors: C
authors: Kranz
authors: Manfred
authors: M
authors: Frick
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology*; D000818:Animals; D001692:Biological Transport / Q000187:drug effects; D002412:Cations / Q000378:metabolism; D005089:Exocytosis / Q000502:physiology; D008168:Lung / Q000187:drug effects / Q000378:metabolism; D008561:Membrane Fusion / Q000187:drug effects*; D018625:Microscopy, Atomic Force / Q000379:methods; D011650:Pulmonary Alveoli / Q000166:cytology / Q000378:metabolism*; D011663:Pulmonary Surfactants / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D058848:Receptors, Purinergic P2X4 / Q000378:metabolism*; D014544:Uridine Triphosphate / Q000494:pharmacology
chemical_list: D002412:Cations; D011663:Pulmonary Surfactants; D058848:Receptors, Purinergic P2X4; D000255:Adenosine Triphosphate; D014544:Uridine Triphosphate