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Abstract ......................................................................................................................3 2.1 Introduction ......................................................................................................4 2.2 Families of GPCRs ..........................................................................................4 2.3 Coupling to G Proteins ....................................................................................5 2.4 GPCR Desensitization......................................................................................6 2.5 Other Signaling Pathways................................................................................7 2.6 Trafficking of GPCRs ......................................................................................9 2.7 Resensitization ...............................................................................................10 2.8 Conclusions ....................................................................................................11 References................................................................................................................11

Many intracellular and intercellular functions are mediated by G protein-coupled receptors (GPCRs). These signal transduction events can occur through the interactions of GPCRs with G proteins and are triggered by a wide variety of inducers such as hormones, neurotransmitters, chemokines, ions, light, and odors. The activation results in a cascade of signal transduction events such as stimulation or inhibition of adenylyl cyclase and activation of phospholipase C. GPCRs must be inactivated or desensitized; this can take place at the receptor or G protein level, generally through phosphorylation mediated by protein kinase A or C. G protein-coupled kinases (GRKs) can also be involved in the desensitization events.