Tissue-Segment Binding Method for Detection of Muscarinic Acetylcholine Receptors in Receptor’s Natural Environment

The pharmacological and biochemical properties of G protein-coupled receptors have been recently revealed to be more complex than originally supposed. Especially, in natural environment or in vivo, some receptors including muscarinic acetylcholine receptor (mAChR) are frequently modified by many factors, so that the receptors may exhibit multiple pharmacological profiles and biochemical functions, which are different from relatively constant and uniform properties originally reported in cell-free preparations and recombinant system. To detect the native properties of receptors occurring in tissues and cells without altering their natural environment and also to solve the discrepancy between the functional affinity obtained by a bioassay approach and the binding affinity estimated from the conventional binding method with cell-free preparations, the tissue segment binding method without homogenization has been developed as a new approach. In this chapter, the detailed protocol of the tissue segment binding method and some unique properties of mAChs in the tissue segments are described.