Extracellular adenosine mediates a multitude of biological effects, including wakefulness, antiarrythmia, bronchoconstriction and response to ischemia and oxidative stress. A family of four G protein-coupled adenosine receptors, A1, α2A, α2B and A3, is responsible for these effects. α2A, which couples to Gs, is expressed in basal ganglia and immune cells. α2A reduces ischemia-induced inflammation; however, α2A antagonists protect from neurodegeneration during Parkinson's disease (Chen, 2003). Caffeine, the most widely used psychoactive drug, is a nonselective adenosine receptor antagonist, but its psychomotor stimulant affect is attributed to α2A expressed on striatal projection neurons (Fisone et al., 2004). Cloned α2A receptor-expressing ChemiBrite cells were made by stable transfection of HEK293 cells with ChemiBrite clytin and the receptor and a promiscuous G protein to couple the receptor to the calcium signaling pathway. These stability-tested cells are ready for luminescent analysis of agonists, antagonists and modulators at the α2A receptor.