Purines and Purinoceptors: Molecular Biology Overview

ATP, in addition to its intracellular roles, acts as an extracellular signaling molecule via a rich array of receptors, which have been cloned and characterized. P1 receptors are selective for adenosine, a breakdown product of ATP, produced after degradation by ectonucleotidases. Four subtypes have been identified, A₁, A_2A, A_2B, and A₃ receptors. P2 receptors are activated by purines and some subtypes also by pyrimidines. P2X receptors are ligand-gated ion channel receptors and seven subunits have been identified; P2Y receptors are G-protein-coupled receptors and eight subtypes have been cloned and characterized to date.