Coordinated release of nucleotides and mucin from human airway epithelial Calu-3 cells.
The efficiency of the mucociliary clearance (MCC) process that removes noxious materials from airway surfaces depends on the balance between mucin secretion, airway surface liquid (ASL) volume, and ciliary beating. Effective mucin dispersion into ASL requires salt and water secretion onto the mucosal surface, but how mucin secretion rate is coordinated with ion and, ultimately, water transport rates is poorly understood. Several components of MCC, including electrolyte and water transport, are regulated by nucleotides in the ASL interacting with purinergic receptors. Using polarized monolayers of airway epithelial Calu-3 cells, we investigated whether mucin secretion was accompanied by nucleotide release. Electron microscopic analyses of Calu-3 cells identified subapical granules that resembled goblet cell mucin granules. Real-time confocal microscopic analyses revealed that subapical granules, labelled with FM 1-43 or quinacrine, were competent for Ca(2+)-regulated exocytosis. Granules containing MUC5AC were apically secreted via Ca(2+)-regulated exocytosis as demonstrated by combined immunolocalization and slot blot analyses. In addition, Calu-3 cells exhibited Ca(2+)-regulated apical release of ATP and UDP-glucose, a substrate of glycosylation reactions within the secretory pathway. Neither mucin secretion nor ATP release from Calu-3 cells were affected by activation or inhibition of the cystic fibrosis transmembrane conductance regulator. In SPOC1 cells, an airway goblet cell model, purinergic P2Y(2) receptor-stimulated increase of cytosolic Ca(2+) concentration resulted in secretion of both mucins and nucleotides. Our data suggest that nucleotide release is a mechanism by which mucin-secreting goblet cells produce paracrine signals for mucin hydration within the ASL.
Kreda
Silvia M
SM
Cystic Fibrosis/Pulmonary Research and Treatment Center, The University of North Carolina at Chapel Hill, 7017 Thurston Bowles Building, Chapel Hill, NC 27599-7248, USA. silvia_kreda@med.unc.edu
Okada
Seiko F
SF
van Heusden
Catharina A
CA
O'Neal
Wanda
W
Gabriel
Sherif
S
Abdullah
Lubna
L
Davis
C William
CW
Boucher
Richard C
RC
Lazarowski
Eduardo R
ER
D000255:Adenosine Triphosphate / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D045744:Cell Line, Tumor; D005089:Exocytosis / Q000502:physiology*; D006801:Humans; D009077:Mucins / Q000378:metabolism*; D009711:Nucleotides / Q000378:metabolism*; D020545:Respiratory Mucosa / Q000378:metabolism*; D022142:Secretory Vesicles / Q000502:physiology; D014539:Uridine Diphosphate Sugars / Q000378:metabolism; D014867:Water / Q000502:physiology*
D009077:Mucins; D009711:Nucleotides; D014539:Uridine Diphosphate Sugars; D014867:Water; D000255:Adenosine Triphosphate; D002118:Calcium