Alveolar epithelial CNGA1 channels mediate cGMP-stimulated, amiloride-insensitive, lung liquid absorption

作者：Wilkinson William J; Benjamin Audra R; De Proost Ian; Orogo Wenn Maria C; Yamazaki Yasuo; Staub Olivier; Morita Takashi; Adriaensen Dirk; Riccardi Daniela; Walters Dafydd V; Kemp Paul J^*

来源：Pflugers Archiv-European Journal of Physiology, 2011, 462(2): 267-279.

DOI：10.1007/s00424-011-0971-0

• Cyclic nucleotide-gated channel
• Epithelial Na+ channel
• Lung liquid homeostasis
• Pseudechetoxin
• Pulmonary oedema
• Alveolar pneumocytes

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 mu M 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 mu M amiloride and that recombinant alpha beta gamma-ENaC were not inhibited by 100 nM PsTx. Importantly, 8Br-cGMP stimulated lung liquid absorption in situ, even in the presence of 50 mu M amiloride. Furthermore, neither L-cis-diltiazem nor PsTx affected the beta(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.

• 出版日期2011-8