[Purinergic receptors--nomenclature and classification of types and subtypes]

The purpose of this review is to present current knowledge regarding purinergic receptors and their subtypes. The main endogenous ligans for these receptors are adenosine and ATP which are released from cells and neurons under various pathophysiological conditions, and adenine nucleotides which are released as contransmiters together with noradrenaline, acetylcholine and substance P. Purinergic receptors which are present in various tissues and mediate numerous physiological effects can be divided into two main groups, P1 (for adenosine) and P2 (for adenine nucleotides) receptors. Both these types are further divided into subtypes. P1 receptors are better characterized than P2 receptors whose classification must be regarded as tentative rather than definitive. P1 receptors are named according to their natural ligand adenosine as A1, A2a, A2b, A3 and possibly A4 receptors. Their characteristics are summarized in tables which also present the main selective agonists and antagonists of their receptors. Since the classification of P2 receptors is still tenative, their nomenclatue does not follow the exact rules which are provided by IUPHAR. P2 receptors are subdivided into these subtypes: P2X, P2Y, P2U, P2T, P2Z and P2D. The article also lists the main agonists and antagonists for these receptors. The introduction of new selective agonists and antagonists not only helps to classify various receptors subtypes of purinoceptors but it also has a big therapeutic potential for various diseases.