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Caffeine is an antagonist of all four adenosine receptor subtypes (A 1, A 2A, A 2B, and A 3), although with varying potencies. [5] [167] The affinity (K D) values of caffeine for the human adenosine receptors are 12 μM at A 1, 2.4 μM at A 2A, 13 μM at A 2B, and 80 μM at A 3. [167]
Studies indicate that, similar to caffeine, simultaneous antagonism of adenosine receptors [9] is responsible for paraxanthine's stimulatory effects. Paraxanthine adenosine receptor binding affinity (21 μM for A1, 32 μM for A2 A, 4.5 μM for A2 B, and >100 for μM for A3) is similar or slightly stronger than caffeine, but weaker than theophylline.
Caffeine keeps you awake by blocking adenosine receptors. Each type of adenosine receptor has different functions, although with some overlap. [3] For instance, both A 1 receptors and A 2A play roles in the heart, regulating myocardial oxygen consumption and coronary blood flow, while the A 2A receptor also has broader anti-inflammatory effects throughout the body. [4]
DMPX (3,7-dimethyl-1-propargylxanthine) is a caffeine analog which displays affinity for A 2 adenosine receptors, in contrast to the A 1 subtype receptors. [1] DMPX had 28 times and 15 times higher potency than caffeine in blocking, respectively, the peripheral and central effects of the adenosine agonist NECA.
Caffeine's principal mode of action is as an antagonist of adenosine receptors in the brain. [ 12 ] Methylxanthines (e.g. caffeine found in coffee, theophylline found in tea, or theobromine found in chocolate) have a purine structure and bind to some of the same receptors as adenosine. [ 13 ]
These receptors may have intrinsic catalytic activity or may be coupled to effector enzymes, or may also be associated to ionic channels. Therefore, there are four main transmembrane receptor types: G protein coupled receptors (GPCRs), tyrosine kinase receptors (RTKs), serine/threonine kinase receptors (RSTKs), and ligand-gated ion channels ...
A crystal structure of the A 2A receptor bound with the agonist NECA and a G protein-mimic has been published in 2016 (PDB code: 5g53). [20] The encoded protein (the A 2A receptor) is abundant in basal ganglia, vasculature, T lymphocytes, and platelets and it is a major target of caffeine, which is a competitive antagonist of this protein. [21]
Receptors may bind with some molecules (ligands) or may interact with physical agents like light, mechanical temperature, pressure, etc. Reception occurs when the target cell (any cell with a receptor protein specific to the signal molecule) detects a signal, usually in the form of a small, water-soluble molecule, via binding to a receptor ...