Extracellular adenosine binds to its 4 receptor subtypes A1, A2A, A2B, and A3 to exert its effect in the CNS.30 A1R and A2AR have high affinities of 70 and 150 nM, respectively, while A2BR and A3R have a distinctly lower affinities of 5100 and 6500 nM, respectively, for adenosine.58 All ARs are present on neurons,52 astrocytes,59 oligodendrocytes,60 and microglia.61
