The cell surface purinergic receptors (purinoceptors) are plasma membrane proteins found in nearly all mammalian tissues including the central nervous system (CNS).1 The history of the purinergic receptors goes back to early 20th century when, for the first time, an observation was made that purines effected cardiovascular physiology.2 Almost half a century later, these receptors were classified based on their endogenous ligands into P1 and P2 categories.3
