A1R

A1R is an abbreviation most often used for the adenosine A1 receptor, a G protein-coupled receptor that binds adenosine. In humans, it is encoded by the ADORA1 gene. A1R is part of the adenosine receptor family, which includes A1, A2A, A2B, and A3 subtypes.

A1R has seven transmembrane helices. It couples preferentially to Gi/o proteins, inhibiting adenylyl cyclase and reducing intracellular cAMP. Activation can also open inward-rectifier potassium channels, causing hyperpolarization and reduced neuronal excitability.

Distribution and function: A1R is highly expressed in the brain, particularly in the hippocampus and cortex, and is also found in the heart and kidney. It modulates neurotransmitter release, participates in sleep-wake regulation, and contributes to neuroprotection during stress. In the heart, activation can slow heart rate and reduce contractility; in the kidney, it influences renal function and diuresis.

Pharmacology: The endogenous ligand is adenosine. A1R activity is modified by agonists and antagonists. Caffeine and theophylline are non-selective antagonists of A1R (and A2A receptors). Selective A1R ligands have been investigated for potential neuroprotective and analgesic uses, though clinical applications are limited by side effects such as sleep disturbance and bradycardia.

Other uses: Outside biology, the term A1R may appear as a model number, product code, or acronym in various fields. When used in scientific literature, A1R almost always refers to the adenosine A1 receptor unless the context specifies otherwise.