Adenosine receptor A1, Adenosine receptor A2B, Adenosine receptor A3 (A1 receptor (A1R), A2B receptor (A2BR), A3 receptor (A3R))

Adenosine receptor A1, A2B, and A3 are three of the four known subtypes of the adenosine (P1 purinergic) receptors, which are G protein-coupled receptors widely distributed throughout the body. These receptors respond to the endogenous nucleoside adenosine and regulate diverse physiological processes, including neurotransmission, cardiac rhythm, inflammation, immune cell activity, and metabolic balance. A1 and A3 typically lead to a reduction in cAMP levels, while A2B stimulates its production, resulting in wide-ranging effects across tissues. These receptors are considered important therapeutic targets for diseases such as cardiovascular and neurodegenerative disorders, cancer, diabetes, and inflammatory conditions. Numerous clinically used and experimental drugs (such as caffeine, theophylline, BAY60-6583, and NECA) act on these receptors, but effective therapeutic targeting is challenged by issues of selectivity, side effects, dose-limiting toxicity, and context-specific physiological responses. Note: Each subtype (A1, A2B, A3) is technically its own target, with unique tissue distributions, signaling mechanisms, and therapeutic implications. The current query, combining all three, may not reflect best practice in target annotation.

Other names

P1 purinergic receptor A1 (for A1)P1 purinergic receptor A2B (for A2B)P1 purinergic receptor A3 (for A3)AR A1, AR A2B, AR A3ADORA1, ADORA2B, ADORA3 (gene names)

Agonists or antagonists modulate G protein-coupled signaling: A1 and A3 generally inhibit adenylyl cyclase via Gi/o proteins, decreasing cAMP; A2B stimulates adenylyl cyclase via Gs proteins, increasing cAMP. Some also act via Gq proteins, affecting phospholipase C and calcium signaling. Drug effects include alteration of neurotransmitter release, immune cell function, vascular tone, and metabolic balance. Non-selective antagonism by caffeine/theophylline provides CNS stimulation and bronchodilation.