The evidence for two opposite, ATP-generating and ATP-consuming, extracellular pathways on endothelial and lymphoid cells

Biochem J. 2002 Oct 1;367(Pt 1):121-8. doi: 10.1042/BJ20020439.


Extracellular purines are important signalling molecules in the vasculature that are regulated by a network of cell surface ectoenzymes. By using human endothelial cells and normal and leukaemic lymphocytes as enzyme sources, we identified the following purine-converting ectoenzymes: (1) ecto-nucleotidases, NTP diphosphohydrolase/CD39 (EC and ecto-5'-nucleotidase/CD73 (EC; (2) ecto-nucleotide kinases, adenylate kinase (EC and nucleoside diphosphate kinase (EC; (3) ecto-adenosine deaminase (EC Evidence for this was obtained by using enzyme assays with (3)H-labelled nucleotides and adenosine as substrates, direct evaluation of gamma-phosphate transfer from [gamma-(32)P]ATP to AMP/NDP, and bioluminescent measurement of extracellular ATP synthesis. In addition, incorporation of radioactivity into an approx. 20 kDa surface protein was observed following incubation of Namalwa B cells with [gamma-(32)P]ATP. Thus two opposite, ATP-generating and ATP-consuming, pathways coexist on the cell surface, where basal ATP release, re-synthesis of high-energy phosphoryls, and selective ecto-protein phosphorylation are counteracted by stepwise nucleotide breakdown with subsequent adenosine inactivation. The comparative measurements of enzymic activities indicated the predominance of the nucleotide-inactivating pathway via ecto-nucleotidase reactions on the endothelial cells. The lymphocytes are characterized by counteracting ATP-regenerating/adenosine-eliminating phenotypes, thus allowing them to avoid the lymphotoxic effects of adenosine and maintain surrounding ATP at a steady-state level. These results are in agreement with divergent effects of ATP and adenosine on endothelial function and haemostasis, and provide a novel regulatory mechanism of local agonist availability for nucleotide- or nucleoside-selective receptors within the vasculature.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • 5'-Nucleotidase / biosynthesis
  • Adenosine / metabolism
  • Adenosine Deaminase / chemistry
  • Adenosine Triphosphate / metabolism*
  • Cell Membrane / metabolism
  • Cells, Cultured
  • Endothelium, Vascular / cytology
  • Endothelium, Vascular / metabolism*
  • Enzyme-Linked Immunosorbent Assay
  • Flow Cytometry
  • Humans
  • Immunoblotting
  • Jurkat Cells
  • Kinetics
  • Lymphocytes / metabolism
  • Models, Biological
  • Phosphorylation
  • Purines / metabolism
  • Radioligand Assay
  • Time Factors
  • Tumor Cells, Cultured


  • Purines
  • Adenosine Triphosphate
  • 5'-Nucleotidase
  • Adenosine Deaminase
  • Adenosine