In vitro muscarinic receptor radioligand-binding assays

G-protein-coupled muscarinic receptors (mAChRs), of which there are five subtypes (M(1)-M(5)), are attractive drug targets for a number of disorders. Described in this unit are radioligand-binding assays for defining the selectivity and affinity of chemical agents at the five mAChR subtypes. Detailed methodologies and troubleshooting strategies are provided for saturation-binding studies, to estimate K(D) and B(max) values, and for competition-binding studies to estimate K(i) values. Emphasis is placed on experimental details that are critical for executing a robust and reliable assay.