Ca2+-dependent ATP release from A549 cells involves synergistic autocrine stimulation by coreleased uridine nucleotides

J Physiol. 2007 Oct 15;584(Pt 2):419-35. doi: 10.1113/jphysiol.2007.133314. Epub 2007 Aug 16.


Extracellular ATP is a potent surfactant secretagogue but its origin in the alveolus, its mechanism(s) of release and its regulatory pathways remain unknown. Previously, we showed that hypotonic swelling of alveolar A549 cells induces Ca(2+)-dependent secretion of several adenosine and uridine nucleotides, implicating regulated exocytosis. In this study, we examined sources of Ca(2+) for the elevation of intracellular Ca(2+) concentration ([Ca(2+)](i)) evoked by acute 50% hypotonic stress and the role of autocrine purinergic signalling in Ca(2+)-dependent ATP release. We found that ATP release does not directly involve Ca(2+) influx from extracellular spaces, but depends entirely on Ca(2+) mobilization from intracellular stores. The [Ca(2+)](i) response consisted of slowly rising elevation, representing mobilization from thapsigargin (TG)-insensitive stores and a superimposed rapid spike due to Ca(2+) release from TG-sensitive endoplasmic reticulum (ER) Ca(2+) stores. The latter could be abolished by hydrolysis of extracellular triphospho- and diphosphonucleotides with apyrase; blocking P2Y(2)/P2Y(6) receptors of A549 cells with suramin; blocking UDP receptors (P2Y(6)) with pyridoxal phosphate 6-azophenyl-2',4'-disulfonic acid (PPADS); emptying TG-sensitive stores downstream with TG or caffeine in Ca(2+)-free extracellular solution; or blocking the Ca(2+)-release inositol 1,4,5-triphosphate receptor channel of the ER with 2-aminoethyldiphenylborinate. These data demonstrate that the rapid [Ca(2+)](i) spike results from the autocrine stimulation of IP(3)/Ca(2+)-coupled P2Y, predominantly P2Y(6), receptors, accounting for approximately 70% of total Ca(2+)-dependent ATP release evoked by hypotonic shock. Our study reveals a novel paradigm in which stress-induced ATP release from alveolar cells is amplified by the synergistic autocrine/paracrine action of coreleased uridine and adenosine nucleotides. We suggest that a similar mechanism of purinergic signal propagation operates in other cell types.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adenosine Triphosphate / metabolism*
  • Apyrase / pharmacology
  • Autocrine Communication*
  • Caffeine / pharmacology
  • Calcium / metabolism*
  • Calcium Signaling* / drug effects
  • Calcium-Transporting ATPases / antagonists & inhibitors
  • Calcium-Transporting ATPases / metabolism
  • Cell Line, Tumor
  • Endoplasmic Reticulum / drug effects
  • Endoplasmic Reticulum / metabolism
  • Enzyme Inhibitors / pharmacology
  • Epithelial Cells / drug effects
  • Epithelial Cells / metabolism*
  • Epithelial Cells / pathology
  • Humans
  • Hydrolysis
  • Hypotonic Solutions
  • Inositol 1,4,5-Trisphosphate Receptors / antagonists & inhibitors
  • Inositol 1,4,5-Trisphosphate Receptors / metabolism
  • Lung Neoplasms / metabolism*
  • Lung Neoplasms / pathology
  • Osmotic Pressure
  • Paracrine Communication*
  • Purinergic P2 Receptor Antagonists
  • Pyridoxal Phosphate / analogs & derivatives
  • Pyridoxal Phosphate / pharmacology
  • Receptors, Purinergic P2 / metabolism
  • Receptors, Purinergic P2Y2
  • Suramin / pharmacology
  • Thapsigargin / pharmacology
  • Time Factors
  • Uracil Nucleotides / metabolism*


  • Enzyme Inhibitors
  • Hypotonic Solutions
  • Inositol 1,4,5-Trisphosphate Receptors
  • P2RY2 protein, human
  • Purinergic P2 Receptor Antagonists
  • Receptors, Purinergic P2
  • Receptors, Purinergic P2Y2
  • Uracil Nucleotides
  • purinoceptor P2Y6
  • pyridoxal phosphate-6-azophenyl-2',4'-disulfonic acid
  • Caffeine
  • Pyridoxal Phosphate
  • Suramin
  • Thapsigargin
  • Adenosine Triphosphate
  • Apyrase
  • Calcium-Transporting ATPases
  • Calcium