Receptor-promoted exocytosis of airway epithelial mucin granules containing a spectrum of adenine nucleotides

J Physiol. 2010 Jun 15;588(Pt 12):2255-67. doi: 10.1113/jphysiol.2009.186643. Epub 2010 Apr 26.


Purinergic regulation of airway innate defence activities is in part achieved by the release of nucleotides from epithelial cells. However, the mechanisms of airway epithelial nucleotide release are poorly understood. We have previously demonstrated that ATP is released from ionomycin-stimulated airway epithelial goblet cells coordinately with mucin exocytosis, suggesting that ATP is released as a co-cargo molecule from mucin-containing granules. We now demonstrate that protease-activated-receptor (PAR) agonists also stimulate the simultaneous release of mucins and ATP from airway epithelial cells. PAR-mediated mucin and ATP release were dependent on intracellular Ca(2+) and actin cytoskeleton reorganization since BAPTA AM, cytochalasin D, and inhibitors of Rho and myosin light chain kinases blocked both responses. To test the hypothesis that ATP is co-released with mucin from mucin granules, we measured the nucleotide composition of isolated mucin granules purified based on their MUC5AC and VAMP-8 content by density gradients. Mucin granules contained ATP, but the levels of ADP and AMP within granules exceeded by nearly 10-fold that of ATP. Consistent with this finding, apical secretions from PAR-stimulated cells contained relatively high levels of ADP/AMP, which could not be accounted for solely based on ATP release and hydrolysis. Thus, mucin granules contribute to ATP release and also are a source of extracellular ADP and AMP. Direct release of ADP/AMP from mucin granules is likely to provide a major source of airway surface adenosine to signal in a paracrine faction ciliated cell A(2b) receptors to activate ion/water secretion and appropriately hydrate goblet cell-released mucins.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Actin Cytoskeleton / metabolism
  • Adenine Nucleotides / metabolism*
  • Adenosine Diphosphate / metabolism
  • Adenosine Monophosphate / metabolism
  • Adenosine Triphosphate / metabolism
  • Calcium / metabolism
  • Cell Line, Tumor
  • Chelating Agents / pharmacology
  • Exocytosis* / drug effects
  • Goblet Cells / drug effects
  • Goblet Cells / metabolism*
  • Humans
  • Hydrolysis
  • Mucin 5AC / metabolism*
  • Myosin-Light-Chain Kinase / antagonists & inhibitors
  • Myosin-Light-Chain Kinase / metabolism
  • Peptides / pharmacology
  • Protein Kinase Inhibitors / pharmacology
  • R-SNARE Proteins / metabolism
  • Receptors, Proteinase-Activated / agonists
  • Receptors, Proteinase-Activated / metabolism*
  • Respiratory Mucosa / drug effects
  • Respiratory Mucosa / metabolism*
  • Secretory Vesicles / drug effects
  • Secretory Vesicles / metabolism*
  • Thrombin / pharmacology
  • rho-Associated Kinases / antagonists & inhibitors
  • rho-Associated Kinases / metabolism


  • Adenine Nucleotides
  • Chelating Agents
  • MUC5AC protein, human
  • Mucin 5AC
  • Peptides
  • Protein Kinase Inhibitors
  • R-SNARE Proteins
  • Receptors, Proteinase-Activated
  • Adenosine Monophosphate
  • Adenosine Diphosphate
  • Adenosine Triphosphate
  • rho-Associated Kinases
  • Myosin-Light-Chain Kinase
  • Thrombin
  • Calcium