A2A Receptor

The A2A receptor, or A2A adenosine receptor, is a cell-surface receptor activated by the signaling molecule adenosine. It is one of four adenosine receptor subtypes, alongside A1, A2B, and A3, and belongs to the G-protein-coupled receptor family. A2A receptors are expressed in several tissues, including the nervous, cardiovascular, and immune systems .^1,2

A2A receptors primarily couple to stimulatory G proteins, particularly Gs and, in parts of the brain such as the striatum, Golf. Activation of these G proteins stimulates adenylyl cyclase and increases production of the intracellular signaling molecule cyclic AMP (cAMP). A2A receptor signaling can thereby influence enzyme activity, gene expression, ion-channel function, and other cellular processes, depending on the cell involved .^1,2

In the brain, A2A receptors are particularly abundant in the striatum, a region involved in motor control and other functions. There, A2A receptor signaling interacts closely with dopamine D2 receptor signaling. A2A receptors also occur in immune cells and blood vessels, where their activation can influence inflammatory responses and vascular tone .¹

The A2A receptor differs from the A1 receptor in its principal signaling pathway. A2A receptors generally stimulate adenylyl cyclase and increase cAMP, whereas A1 receptors mainly couple to inhibitory Gi/o proteins and reduce adenylyl cyclase activity. Caffeine antagonizes both A1 and A2A receptors at concentrations relevant to its common stimulant effects, thereby reducing adenosine signaling through these receptors .¹