Correlation Between Adenine Nucleotide-Induced Cyclic AMP Elevation and Extracellular Adenosine Formation in NG108-15 Cells

We previously demonstrated that extracellular adenine nucleotides induced cyclic AMP elevation in NG108-15 cells. This response was resistant to adenosine deaminase (ADA) and the ecto-5'-nucleotidase (CD73) inhibitor alpha,beta-methylene ADP (alpha,beta-MeADP), but was inhibited by both P1- and P2-receptor antagonists. In the present study, we investigated the relationship between adenine nucleotide-induced cyclic AMP elevation and extracellular adenosine formation. ATP, AMP and beta,gamma-methylene ATP (beta,gamma-MeATP) were time-dependently metabolized to adenosine in NG108-15 cells. Adenosine formations from ATP, AMP and beta,gamma-MeATP were not affected by alpha,beta-MeADP, but suppressed by the P2-receptor antagonist pyridoxalphosphate-6-azophenyl-2',4'-disulphonic acid (PPADS). A close correlation between extracellular adenosine formation and cyclic AMP increasing effects were obtained with several adenine nucleotide agonists in NG108-15 cells as well as their parent cell line C6Bu-1 and N18TG-2 cells, all of which possess functional adenosine A2 receptors. When NG108-15 cells were incubated with [3H]ATP or [3H]AMP in the presence of ADA, [3H]adenosine was found to distribute dominantly on the cell surface. NG108-15 cells expressed mRNA for the ecto-ATPase and nucleotide pyrophosphatase, but not for CD73. These results suggest that local adenosine formation by an ecto-enzyme distinct from CD73 is involved in adenine nucleotide-induced cyclic AMP formation in NG108-15 cells.