title: Alveolar epithelial CNGA1 channels mediate cGMP-stimulated, amiloride-insensitive, lung liquid absorption.
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, amiloride completely ablated it. Thus, transport through alveolar CNGA1 channels, located in type I cells, underlies the amiloride-insensitive component of lung liquid reabsorption. 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.
authors.affiliation: Division of Pathophysiology and Repair, School of Biosciences, Cardiff University, Museum Avenue, Cardiff, UK.
authors.forename: William J
authors.initials: WJ
authors.lastname: Wilkinson
authors.forename: Audra R
authors.initials: AR
authors.lastname: Benjamin
authors.forename: Ian
authors.initials: I
authors.lastname: De Proost
authors.forename: Maria C
authors.initials: MC
authors.lastname: Orogo-Wenn
authors.forename: Yasuo
authors.initials: Y
authors.lastname: Yamazaki
authors.forename: Olivier
authors.initials: O
authors.lastname: Staub
authors.forename: Takashi
authors.initials: T
authors.lastname: Morita
authors.forename: Dirk
authors.initials: D
authors.lastname: Adriaensen
authors.forename: Daniela
authors.initials: D
authors.lastname: Riccardi
authors.forename: Dafydd V
authors.initials: DV
authors.lastname: Walters
authors.forename: Paul J
authors.initials: PJ
authors.lastname: Kemp
mesh_terms: D000042:Absorption; D000584:Amiloride / Q000378:metabolism; D000818:Animals; D051402:Aquaporin 5 / Q000378:metabolism; D001692:Biological Transport / Q000502:physiology; D006152:Cyclic GMP / Q000031:analogs & derivatives / Q000378:metabolism*; D054815:Cyclic Nucleotide-Gated Cation Channels / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D004232:Diuretics / Q000378:metabolism; D004546:Elapid Venoms / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism*; D005260:Female; D057809:HEK293 Cells; D006801:Humans; D015640:Ion Channel Gating / Q000502:physiology; D008168:Lung / Q000166:cytology / Q000378:metabolism*; D008297:Male; D018408:Patch-Clamp Techniques; D020033:Protein Isoforms / Q000235:genetics / Q000378:metabolism*; D011650:Pulmonary Alveoli / Q000378:metabolism*; D051381:Rats; D017208:Rats, Wistar
chemical_list: C496040:Aqp5 protein, rat; D051402:Aquaporin 5; C568128:CNGA1 protein, rat; D054815:Cyclic Nucleotide-Gated Cation Channels; D004232:Diuretics; D004546:Elapid Venoms; D020033:Protein Isoforms; C016276:8-bromocyclic GMP; D000584:Amiloride; D006152:Cyclic GMP