G protein-coupled receptors (GPCRs) are important conformational "switches" in transmembrane signal transduction and represent the largest gene family in the human genome reflecting the importance of GPCRs as targets for hormones, neurotransmitters and local mediators in virtually any cell type of the human body. Since GPCRs discriminate well between natural and synthetic ligands and because of their localization in the plasma membrane, they are the single most important class of drug targets. With its particular emphasis on the constitutive activity of GPCRs, this book recognizes a biological process that has not yet been covered by existing books on GPCRs. An international team of highly distinguished authors discusses current models and concepts in detail, introducing the advances made in our understanding GPCR activation and constitutive activity. In addition, the text provides an overview on the methods of investigating GPCR activity. From the contents: PART I: GENERAL CONCEPTS Models of constitutive activity Molecular mechanisms of GPCR activation Impact of G proteins on constitutive GPCR activity Physiological and therapeutic relevance of constitutive GPCR activity Methodological Approaches PART II: SELECTED GPCR SYSTEMS Chemokine receptors and human disease α-Adrenoceptors β-Adrenoceptors Muscarinic Acetylcholine Receptors Histamine receptors 5-HT receptors Virally pirated Chemokine receptors and human disease Illustrated by numerous experimental examples, schemes and methodological advice for analyzing GPCRs, this is a highly practical reference for pharmaceutical chemists, physiologists and medical researchers in academia and industry.