The receptors for purines (purinergic receptors) can be separated into two groups: P1 (adenosine receptors) and P2 (ATP receptors). P2 is further divided into two families, G protein-coupled P2Y receptors, and ATP-gated cation channels, called P2X receptors.

P2X receptors are widely expressed in mammalian cells, where they can be broadly differentiated into three groups. The first group is activated not only by ATP, but also by its analog, alpha-beta-methylene ATP. The second group is activated only by ATP. The third group of receptors (termed P2Z) is distinguished by the fact that the channel opening is followed by cell permeabilization and lysis if the agonist application continues for more than a few seconds. P2X1 and P2X3 subunits belong to the first group with two activators. P2X2, P2X4, and P2X5 fall in the second group, activated just by ATP. P2X6 is not expressed readily, and P2X7 is similar to the P2Z receptors.