Adenosine Receptors in the Lungs

The ubiquitous adenine nucleoside adenosine (Ado), which plays an important role in cellular energetics, is released from cells under physiologic and pathophysiologic conditions. Another source of extracellular Ado is rapid degradation of extracellular adenosine 5′-triphosphate (ATP) by ectoenzymes. Extracellular Ado acts as an autocrine and paracrine agent by the activation of G protein-coupled cell surface receptors (GPCRs), designated as A(1), A(2A), A(2B), and A(3). Almost four decades ago, published data have indicated that Ado could play a role in immune-mediated histamine release from pulmonary mast cells. Since then, numerous studies have indicated that Ado’s signal transductions are involved in various pulmonary pathologies including asthma and COPD. This chapter is a succinct review of recent studies in this field.