Illustration of the secondary structure of the adenosine A2A receptor. This is a transmembrane protein that has a number of important roles in the human body. In the heart it regulates myocardial (heart muscle) oxygen consumption and coronary blood flow. In the brain it regulates the release of neurotransmitters, especially dopamine and glutamate. It has an anti-inflammatory affect on the immune system. The receptor is also the target of caffeine and produces its stimulant effects.