title: Nucleotide release provides a mechanism for airway surface liquid homeostasis.
abstract: Nucleotides within the airway surface liquid (ASL) regulate airway epithelial ion transport rates by Ca(2+) -and protein kinase C-dependent mechanisms via activation of specific P2Y receptors. Extracellular adenine nucleotides also serve as precursors for adenosine, which promotes cyclic AMP-mediated activation of the cystic fibrosis transmembrane regulator chloride channel via A(2b) adenosine receptors. A biological role for extracellular ATP in ASL volume homeostasis has been suggested by the demonstration of regulated ATP release from airway epithelia. However, nucleotide hydrolysis at the airway surface makes it difficult to assess the magnitude of ATP release and the relative abundance of adenyl purines and, hence, to define their biological functions. We have combined ASL microsampling and high performance liquid chromatography analysis of fluorescent 1,N(6)-ethenoadenine derivatives to measure adenyl purines in ASL. We found that adenosine, AMP, and ADP accumulated in high concentrations relative to ATP within the ASL covering polarized primary human normal or cystic fibrosis airway epithelial cells. By using immortalized epithelial cell monolndogenayers that eously express a luminal A(2b) adenosine receptor, we found that basal as well asforskolin-promoted cyclic AMP production was reduced by exogenous adenosine deaminase, suggesting that A(2b) receptors sense endogenous adenosine within the ASL. The physiological role of adenosine was further established by illustrating that adenosine removal or inhibition of adenosine receptors in primary cultures impaired ASL volume regulation. Our data reveal a complex pattern of nucleotides/nucleosides in ASL under resting conditions and suggest that adenosine may play a key role in regulating ASL volume homeostasis.
authors.affiliation: Cystic Fibrosis/Pulmonary Research and Treatment Center, University of North Carolina School of Medicine, 7017 Thurston-Bowles Building, Chapel Hill, NC 72599, USA. Eduardo_Lazarowski@med.unc.edu
authors.forename: Eduardo R
authors.initials: ER
authors.lastname: Lazarowski
authors.forename: Robert
authors.initials: R
authors.lastname: Tarran
authors.forename: Barbara R
authors.initials: BR
authors.lastname: Grubb
authors.forename: Catharina A
authors.initials: CA
authors.lastname: van Heusden
authors.forename: Seiko
authors.initials: S
authors.lastname: Okada
authors.forename: Richard C
authors.initials: RC
authors.lastname: Boucher
mesh_terms: D000225:Adenine / Q000737:chemistry*; D000241:Adenosine / Q000737:chemistry / Q000378:metabolism; D000244:Adenosine Diphosphate / Q000378:metabolism; D000249:Adenosine Monophosphate / Q000378:metabolism; D000255:Adenosine Triphosphate / Q000737:chemistry / Q000378:metabolism; D002460:Cell Line; D002478:Cells, Cultured; D002851:Chromatography, High Pressure Liquid; D000242:Cyclic AMP / Q000378:metabolism; D003550:Cystic Fibrosis / Q000378:metabolism*; D019005:Cystic Fibrosis Transmembrane Conductance Regulator / Q000378:metabolism*; D004305:Dose-Response Relationship, Drug; D049454:Firefly Luciferin / Q000378:metabolism; D006801:Humans; D006868:Hydrolysis; D008156:Luciferases / Q000378:metabolism; D018613:Microscopy, Confocal; D009092:Mucous Membrane / Q000473:pathology; D009711:Nucleotides / Q000737:chemistry; D011493:Protein Kinase C / Q000378:metabolism*; D011687:Purines / Q000737:chemistry / Q000378:metabolism; D043704:Receptor, Adenosine A2B / Q000378:metabolism; D020545:Respiratory Mucosa / Q000473:pathology; D012137:Respiratory System / Q000378:metabolism; D013997:Time Factors; D014132:Trachea / Q000166:cytology
chemical_list: C505032:CFTR protein, human; D009711:Nucleotides; D011687:Purines; D043704:Receptor, Adenosine A2B; D019005:Cystic Fibrosis Transmembrane Conductance Regulator; D000249:Adenosine Monophosphate; D049454:Firefly Luciferin; D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D000242:Cyclic AMP; D008156:Luciferases; D011493:Protein Kinase C; D000225:Adenine; D000241:Adenosine