[S]GTPγS (Guanosine-5'-O-(γ-thio)triphosphate-[S]) Binding Scintillation Proximity Assay Experiments in Postmortem Brain Tissue.

Heterotrimeric guanine nucleotide-binding proteins (G proteins) are the very first effector in signal transduction events triggered by G-protein-coupled receptors (GPCRs). One of the most widely used approaches for determining GPCR activity in native tissue is based on the binding of [S]GTPγS. Classically, an heterogeneous procedure including a filtration step has been used, but a modification of the protocol including an immunoprecipitation step has allowed the specific discrimination of the contribution of the different Gα subunit subtypes to the effect of each ligand. Nowadays, that the concept of functional selectivity has been demonstrated for several ligands and GPCRs, information obtained from this methodological approach will be very useful for broadening the knowledge of GPCRs signaling profiles and describing the effect of different ligands over them. In this chapter we will describe the detailed protocol of antibody-capture [S]GTPγS scintillation proximity assay (SPA) in order to provide the reader with comprehensive guidelines to study receptor-mediated functional activation of different Gα-protein subtypes in native mammalian brain membranes. In addition, advantages and limitations of this method will be described, as well as future direction in the application of this approach indicated.