Physiological, pharmacological and molecular biological data generated over the past three decades have demonstrated the existence of two major families of extracellular receptors, the P1, a family of four G-protein coupled receptors and the P2, a family of at least 12 receptors responsive to purine (ATP, ADP) and pyrimidine (UTP) nucleotides through which adenosine and ATP can function as extracellular messengers. The present two-part volume represents an integrated compendium of invited chapters by leading researchers in the area focusing on advances in the understanding of purinergic and...