INTEGRATIVE PHYSIOLOGY Alveolar epithelial CNGA1 channels mediate cGMP-stimulated, amiloride-insensitive, lung liquid absorption William J. Wilkinson & Audra R. Benjamin & Ian De Proost & Maria C. Orogo-Wenn & Yasuo Yamazaki & Olivier Staub & Takashi Morita & Dirk Adriaensen & Daniela Riccardi & Dafydd V. Walters & Paul J. Kemp Received: 18 March 2011 /Revised: 21 April 2011 /Accepted: 22 April 2011 # Springer-Verlag 2011 Abstract Impairment of lung liquid absorption can lead to severe respiratory symptoms, such as those observed in pulmonary oedema. In the adult lung, liquid absorption is driven by cation transport through two pathways: a well- established amiloride-sensitive Na + channel (ENaC) and, more controversially, an amiloride-insensitive channel that may belong to the cyclic nucleotide-gated (CNG) channel family. Here, we show robust CNGA1 (but not CNGA2 or CNGA3) channel expression principally in rat alveolar type I cells; CNGA3 was expressed in ciliated airway epithelial cells. Using a rat in situ lung liquid clearance assay, CNG channel activation with 1 mM 8Br-cGMP resulted in an approximate 1.8-fold stimulation of lung liquid absorption. There was no stimulation by 8Br-cGMP when applied in the presence of either 100 μM L-cis-diltiazem or 100 nM pseudechetoxin (PsTx), a specific inhibitor of CNGA1 channels. Channel specificity of PsTx and amiloride was confirmed by patch clamp experiments showing that CNGA1 channels in HEK 293 cells were not inhibited by 100 μM amiloride and that recombinant αβγ-ENaC were not inhibited by 100 nM PsTx. Importantly, 8Br-cGMP stimulated lung liquid absorption in situ, even in the presence of 50 μM amiloride. Furthermore, neither L-cis- diltiazem nor PsTx affected the β 2 -adrenoceptor agonist- stimulated lung liquid absorption, but, as expected, ami- loride completely ablated it. Thus, transport through alveolar CNGA1 channels, located in type I cells, underlies the amiloride-insensitive component of lung liquid reab- sorption. Furthermore, our in situ data highlight the potential of CNGA1 as a novel therapeutic target for the treatment of diseases characterised by lung liquid overload. Keywords Cyclic nucleotide-gated channel . Epithelial Na + channel . Lung liquid homeostasis . Pseudechetoxin . Pulmonary oedema . Alveolar pneumocytes Introduction Maintaining a lung lumen relatively free of liquid is crucially important for normal lung function, good gas exchange and health. The volume of liquid normally present in the lung lumen (about 0.37 ml kg -1 body weight; for discussion, see [55]) appears to be tightly controlled. Excess volume leads to respiratory symptoms, as exempli- William J. Wilkinson and Audra R. Benjamin contributed equally to this work. W. J. Wilkinson : I. De Proost : D. Riccardi : P. J. Kemp (*) Division of Pathophysiology and Repair, School of Biosciences, Cardiff University, Museum Avenue, Cardiff CF10 3AX, UK e-mail: kemp@cf.ac.uk A. R. Benjamin : M. C. Orogo-Wenn : D. V. Walters Division of Clinical Sciences, St. George’ s University of London, London, UK I. De Proost : D. Adriaensen Laboratory of Cell Biology and Histology, Department of Veterinary Sciences, University of Antwerp, Antwerp, Belgium Y. Yamazaki : T. Morita Department of Biochemistry, Meiji Pharmaceutical University, Noshio, Kiyose, Tokyo, Japan O. Staub Department of Pharmacology and Toxicology, University of Lausanne, Lausanne, Switzerland Pflugers Arch - Eur J Physiol DOI 10.1007/s00424-011-0971-0