Adenosine is a molecule that binds to certain receptors in the body, called G protein-coupled receptors (GPCRs). When adenosine binds to these receptors, it activates two different types of GPCRs, called Gs and Gi. Adenosine is created from a molecule called ATP or adenosine triphosphate. This molecule is stored in a #vesicle in the #presynaptic #neuron. When an action potential occurs, the vesicle fuses with the presynaptic #membrane and releases ATP and glutamate.