G protein-coupled receptor trafficking and signalling in the enteric nervous system: the past, present and future

G protein-coupled receptors (GPCRs) enable cells to detect and respond to changes in their extracellular environment. With over 800 members, the GPCR family includes receptors for a diverse range of agonists including olfactants, neurotransmitters and hormones. Importantly, GPCRs represent a major therapeutic target, with approximately 50 % of all current drugs acting at some aspect of GPCR signalling (Audet and Bouvier 2008). GPCRs are widely expressed by all cell types in the gastrointestinal (GI) tract and are major regulators of every aspect of gut function. Many GPCRs are internalised upon activation, and this represents one of the mechanisms through which G protein-signalling is terminated. The latency between the endocytosis of GPCRs and their recycling and resensitization is a major determinant of the cell’s ability to respond to subsequent exposure to agonists.