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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 exerts its psychoactive and sympathomimetic effects by acting as an antagonist at adenosine receptors. [9] d9-Caffeine was assessed for human adenosine receptor antagonism at the four receptor subtypes: A1, A2A, A2B, and A3, and found to have similar adenosine receptor affinity as caffeine. [3]
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]
In the human body, caffeine blocks adenosine receptors A 1 and A 2A. [5] Adenosine is a by-product of cellular activity: the stimulation of adenosine receptors produces sedation and a desire for sleep. Caffeine's ability to block these receptors means the levels of the body's natural stimulants, dopamine and norepinephrine, continue at higher ...
In small doses, caffeine can improve endurance. [22] It has also been shown to delay the onset of fatigue in exercise. The most probable mechanism for the delay of fatigue is through the obstruction of adenosine receptors in the central nervous system. [23] Adenosine is a neurotransmitter that decreases arousal and increases sleepiness.