Figure 1.

Schematic of the intra- and extra-cellular ATP/adenosine signaling cascades. Intracellularly, adenosine is formed from AMP by cytosolic 5′-nucleotidase. Adenosine kinase and adenosine deaminase convert adenosine to AMP and inosine, respectively. Extracellularly, ATP, ADP, and AMP are converted to adenosine by ecto-5′-nucleotidases. Intracellular and extracellular adenosine levels are regulated by bi-directional equilibrative nucleoside transporters.