Related Experiment Video
Updated: Jun 7, 2026

Quantifying Agonist Activity at G Protein-coupled Receptors
Published on: December 26, 2011
Constitutive activity of GPR40/FFA1 intrinsic or assay dependent?
Leigh A Stoddart1, Graeme Milligan
1Institute of Cell Signalling, School of Biomedical Science, Medical School, University of Nottingham, Nottingham, United Kingdom.
Abstract:
Free fatty acid receptor 1 (FFA1; previously designated GPR40) is a potential therapeutic target for the treatment of diabetes and related metabolic disorders. Agonist-independent or constitutive activity is a feature associated with essentially all G protein-coupled receptors but the extent of this varies substantially between family members. In many situations, detection of such activity can be both assay- and context-dependent and may reflect the presence in the assay of an endogenous agonist. In studies on FFA1, experiments employing cell membrane preparations and the binding of [(35)S]guanosine 5'-O-[γ-thio]triphosphate to G proteins produce data consistent with a high-level constitutive activity of this receptor. Herein, we detail these assays and discuss approaches to determine if this is a measure of intrinsic receptor constitutive activity or if such results reflect the presence of an endogenous agonist. FFA1 is coupled predominantly to G proteins of the Gα(q) subfamily. Activation of the receptor results, therefore, in the transient elevation of intracellular [Ca(2+)]. We also detail assays to measure such signals and consider whether they are appropriate to detect receptor constitutive activity.
More Related Videos
11:49Characterization of G Protein-coupled Receptors by a Fluorescence-based Calcium Mobilization Assay
Published on: July 28, 2014
07:41A Kinetic Fluorescence-based Ca2+ Mobilization Assay to Identify G Protein-coupled Receptor Agonists, Antagonists, and Allosteric Modulators
Published on: February 20, 2018
Related Concept Videos
GPCRs Regulate Adenylyl Cylase Activity
Two...
Activation and Inactivation of G Proteins
G-protein Coupled Receptors
G-protein Coupled Receptors
G Protein-coupled Receptors
GPCRs are also called heptahelical, 7TM, or serpentine receptors, and consist of seven (H1-H7) transmembrane alpha-helices that span the bilayer to form a cylindrical core. The transmembrane helices are connected by three extracellular loops and three...
Transducer Mechanism: G Protein–Coupled Receptors
GPCRs are also called heptahelical, 7TM, or...