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.

Lung epithelia regulate the water flux between gas filled airways and the interstitial compartment in order to maintain organ function. Current methodology to assess transepithelial water transport is limited. We present a D2O dilution method to quantify submicroliter volumes of aqueous solutions on epithelial cell layers. Evaluating D2O/H2O mixtures using mid-infrared (2-25 μm) attenuated total reflection (ATR) spectroscopy, with a resolution of 0.06% vol/vol change, corresponding to 24 nL, was achieved. Using this method, we demonstrate that water transport across NCI-H441 lung epithelial cell layers and apical surface liquid (ASL) volumes are coupled to dexamethasone dependent amiloride-sensitive ion transport. However, contrary to current dogma, electrogenic transport is not rate-limiting for water transport. This clearly indicates the need to directly assess net water rather than ion transport across epithelial cell layers. The presented D2O dilution method enables such direct and quick quantification of transepithelial water transport with high resolution.

Proper apical airway surface hydration is essential to maintain lung function. This hydration depends on well‐balanced water resorption and secretion. The mechanisms involved in resorption are still a matter of debate, especially as the measurement of transepithelial water transport remains challenging. In this study, we combined classical short circuit current (ISC) measurements with a novel D2O dilution method to correlate ion and water transport in order to reveal basic transport mechanisms in lung epithelia. D2O dilution method enabled precise analysis of water resorption with an unprecedented resolution. NCI‐H441 cells cultured at an air–liquid interface resorbed water at a rate of 1.5 ± 0.4 μL/(h cm2). Water resorption and ISC were reduced by almost 80% in the presence of the bulk Cl− channel inhibitor 5‐nitro‐2‐(3‐phenylpropylamino)benzoic acid (NPPB) or amiloride, a specific inhibitor of epithelial sodium channel (ENaC). However, water resorption and ISC were only moderately affected by forskolin or cystic fibrosis transmembrane regulator (CFTR) channel inhibitors (CFTRinh‐172 and glybenclamide). In line with previous studies, we demonstrate that water resorption depends on ENaC, and CFTR channels have only a minor but probably modulating effect on water resorption. However, the major ENaC‐mediated water resorption depends on an apical non‐CFTR Cl− conductance.

Hintergrund: Bei schwerster Erkrankung der Augenoberfläche, bei der eine perforierende Keratoplastik nicht erfolgreich ist, kann die Implantation einer Keratoprothese eine Visusrehabilitation erreichen. Die Osteo-Odonto-Keratoprothese bietet durch die biologische Haptik eine gute Gewebeintegration und damit eine bessere Überlebensrate und geringere Extrusionsrate. Aufgrund der häufig vollständig Hornhautintransparenz stellt die Abschätzung des Visuspontential präoperativ eine besondere Herausforderung dar. Auch während der Implantation einer Keratoprothese oder bei notwendigen intraokularen Revisionseingriffen besteht aufgrund der kleinen zentrale Prothesenoptik und der geometrischen Bedingungen der Prothesenhaptik ein eingeschränkter Einblick auf die periphere Netzhaut, bzw. die Ziliarkörperregion und kann den Eingriff erschweren. Methoden: An 7 Augen von 6 verschiedenen Patienten (6 männlich, 2 weiblich, mittleres Alter 66  9 Jahre) wurde die endoskopische Videoassistenz eingesetzt. Dies erfolgte an drei Augen zur Indikationsprüfung und Abschätzung des Visusopotentials im Rahmen einer 23G-Vitrektomie, an zwei Augen während der Implantation und an 2 Augen bei erforderlichen Revisionseingriffen ebenfalls im Rahmen einer Vitrektomie. Es wurde ein Endoskop mit semirigider Optik und einem Bildleitsystem mit 3000 Pixel und 70° Blickfeld der Firma PolyDiagnost® und 23 G-Trokarsyteme verwendet. Ergebnisse: Die Endoskopie konnte bei allen untersuchten Augen erfolgreich eingesetzt werden. Nur bei 1 von 3 Augen, bei denen sie zur Abschätzung des Visuspotentials durchgeführt wurde, erfolgte im Weiteren die Planung der Keratoprothese, während das Visuspotential befundbedingt bei zwei Augen als unzureichend bewertet wurde. Die Beurteilung von Makula und Papille war jedoch durch die Bildauflösung auf den Ausschluss grober Pathologien limitiert. Bei der Implantation konnte die korrekte Positionierung der posterioren Haptik hinter der Wirtshornhaut visualisiert werden. Mittels Endoskopie-assistierter Vitrektomie konnten retroprothetische Membranen erfolgreich entfernt werden. Schlussfolgerung: Die Endoskopie-Assistenz bietet Vorteile in der Visualisierung sowohl bei der Indikationsstellung, während der Implantation sowie beim Management von Komplikationen nach der Implantation einer Keratoprothese. Die Auflösung des Bildsystems erlaubte jedoch nur eine eingeschränkte Beurteilung. Auch wenn technische Weiterentwicklungen wünschenswert sind, stellt die Endoskopie im Kontext der Keratoprothesenchirurgie schon heute eine wertvolle Ergänzung dar. Abstract (en): Introduction: In severe ocular surface disease where penetrating keratoplasty cannot be successfully performed, implantation of a keratoprosthesis can achieve visual rehabilitation. Osteoodonto keratoprosthesis offers good tissue integration due to its biological haptics, resulting in a better survival rate and lower extrusion rate. Due to the often complete corneal intransparency, the estimation of the visual pontential is challenging. Also, during implantation of a keratoprosthesis or during later intraocular revision surgery, there is a limited field of view of the peripheral retina or ciliary body region. This is due to the small central prosthetic optic and the geometric conditions of the prosthetic haptic. These factors can complicate surgery. Methods: Endoscopic video assistance was used in 7 eyes of 6 different patients (6 male, 2 female, mean age 66  9 years). In 3 eyes the indication was for preoperative estimation of potential visual acuity during a 23G vitrectomy. In 2 eyes it was used during implantation surgery itself, and in 2 eyes during revision surgery and vitrectomy. An endoscope with semirigid optics and an image guidance system with 3000 pixels and 70° field of view from PolyDiagnost® and 23 G trocar system was used. Results: Endoscopy was successfully applied in all eyes examined. In 1 of 3 eyes where endoscopy was performed to estimate the visual potential a keratoprosthesis was planned. In the other two eyes the visual potential was rated insufficient for future keratoprosthesis surgery. Detailed assessment of retina and optic disc was limited to gross pathologies because of low image resolution. During implantation, correct positioning of the posterior haptic behind the host cornea could be visualized. Retroprosthetic membranes could successfully be removed by endoscopy-assisted vitrectomy. Conclusion: Endoscopy assistance offers advantages in visualization both for indication, during implantation and in the management of complications after implantation of a keratoprosthesis. Low resolution of the imaging system limited assessment capabilities. Although technical improvements and miniaturization may enhance its future capabilities, endoscopy in its current form is already a valuable addition in the context of keratoprosthesis surgery