Adenosine A1 and A2 receptors (ADORA1/ADORA2)

Adenosine A1 and A2 receptors are G protein-coupled receptors (GPCRs) that mediate the biological effects of adenosine, a ubiquitous nucleoside involved in energy metabolism and cellular signaling [1.1.2, 1.4.1]. The A1 receptor (ADORA1) is primarily coupled to Gi/o proteins, inhibiting adenylyl cyclase and reducing cAMP levels, which leads to inhibitory effects such as decreased heart rate and suppressed neurotransmitter release in the brain [1.4.1, 1.4.2]. The A2 receptors, including the high-affinity A2A (ADORA2A) and low-affinity A2B (ADORA2B) subtypes, are typically coupled to Gs proteins, stimulating adenylyl cyclase and increasing cAMP to promote vasodilation, inhibit platelet aggregation, and modulate immune responses [1.1.1, 1.4.1]. These receptors are significant therapeutic targets across multiple areas; for instance, A2A antagonists like istradefylline are used as adjunct treatments in Parkinson's disease to enhance dopaminergic signaling, while A2A agonists like regadenoson are employed in cardiac imaging for their vasodilatory properties [1.1.1, 1.4.4]. Non-selective antagonists like caffeine and theophylline are well-known for their stimulant and bronchodilatory effects, respectively, highlighting the broad physiological impact of modulating these receptors [1.1.2, 1.4.1].

Other names

P1 receptorsAdenosine receptorsADORA1ADORA2AADORA2B

Drugs targeting these receptors act as either agonists or antagonists to modulate intracellular signaling pathways. A1 receptor agonists activate Gi proteins to inhibit adenylyl cyclase, decreasing cAMP and opening potassium channels, which slows cardiac conduction [1.4.1, 1.4.2]. A2A receptor agonists activate Gs proteins to increase cAMP, leading to smooth muscle relaxation and vasodilation [1.1.1, 1.4.1]. Conversely, A2A antagonists block the inhibitory effect of adenosine on dopamine D2 receptors in the striatum, thereby improving motor function in Parkinson's disease [1.2.1, 1.3.1]. Non-selective antagonists like caffeine block both A1 and A2A receptors, preventing adenosine-mediated sedation and promoting alertness [1.1.2, 1.4.1].