Fig. 2

Adenosine is a purine nucleoside produced by many different organs throughout the body. Extracellular adenosine is a primordial molecule that is produced by many cell types in the body. These include heart, lung, gut, brain and immune cells. Adenosine produced by these cells can in turn act on the producing cells or on adjacent cells to modulate function. Extracellular adenosine is produced from ATP released in the extracellular environment upon cell damage and is converted to ADP and AMP by CD39. AMP is further converted to adenosine by CD73. Extracellular adenosine binds to its receptors expressed on the same cell or adjacent cells to mediate its function. Adenosine is rapidly degraded to inosine by adenosine deaminase