Radioligand Binding at Muscarinic Receptors

Abstract

Five subtypes of muscarinic acetylcholine receptors denoted M1 through M5 have been cloned. Muscarinic receptors mediate a wide array of physiological functions and impairment of muscarinic signaling is involved in numerous pathological conditions including Alzheimer’s disease and schizophrenia. Reliable radioligand binding techniques allow study of involvement of individual muscarinic receptor subtypes in the physiology and pathology of muscarinic signaling, and study of the structure of muscarinic receptors and structure-activation relationship of muscarinic ligands. Here we discuss the current state of knowledge of radioligand binding experiments at muscarinic receptors from the perspective of available radioligands and selective unlabeled muscarinic ligands. We relate binding properties of muscarinic ligands to experimental design (e.g., nonspecific binding determination, incubation conditions, buffers, temperature). We also list tissue/cell sources of muscarinic receptors suitable for radioligand binding studies and describe procedures of cell and tissue preparation for radioligand binding experiments. We also describe several techniques of receptor-bound ligand separation applicable at muscarinic receptors and provide basic information for binding data analysis.