Figure 14.

Nucleotide signaling. Nucleotides are signaling molecules that regulate multiple physiological processes, including neurotransmission and inflammation. Extracellular ATP activates a family of ionotropic receptors (P2X) and metabotropic receptors (P2Y). Extracelluar ADP activate P2Y receptors. Extracellular adenosine activates G-protein-coupled cell-surface receptors, which are divided into four subtypes: A1, A2A, A2B, and A3 receptors. (Adapted from http://en.wikipedia.org/wiki/Purinergic_receptor#mediaviewer/File:Purinergic_signalling.jpg.)