Related Experiment Video
Updated: Jun 2, 2026
10:13
Measuring G-protein-coupled Receptor Signaling via Radio-labeled GTP Binding
Published on: June 9, 2017
Antagonists show GTP-sensitive high-affinity binding to the sigma-1 receptor
J M Brimson1, C A Brown, S T Safrany
1Department of Pharmacy and Pharmacology, University of Bath, Bath, UK.
British Journal of Pharmacology
|April 14, 2011
Summary
Sigma-1 receptor antagonists bind to high- and low-affinity states, unlike agonists. Functional responses require binding to an unidentified low-affinity target, suggesting a revised understanding of sigma-1 receptor activity.
Area of Science:
- Pharmacology
- Cell Biology
- Neuroscience
Background:
- Sigma-1 receptors possess atypical characteristics, including potentially two transmembrane domains.
- Antagonists typically require higher doses than their affinities suggest for biological effects.
Purpose of the Study:
- To reassess the binding characteristics of sigma-1 receptor ligands.
- To investigate the distinct binding states of sigma-1 receptor antagonists and agonists.
- To explore the relationship between ligand binding and functional responses.
Main Methods:
- Radioligand saturation and competition binding assays using [³H]-(+)-pentazocine.
- Assessment of metabolic activity via MTS assay.
- Analysis of calcium signaling using Fura-2 dye.
Main Results:
- Sigma-1 receptor antagonists exhibit GTP- and suramin-sensitive high-affinity binding, distinct from agonists.
- Functional responses, including calcium signaling and metabolic activity, are linked to sigma-1 receptor binding.
- These functional responses necessitate binding to an unidentified, low-affinity target.
Conclusions:
- Sigma-1 receptors are coupled to G proteins, an interaction evident during antagonist binding analysis.
- The specific G protein involved in this coupling remains to be identified.
- The established concepts of agonist and antagonist actions at the sigma-1 receptor warrant re-evaluation.
Related Concept Videos
01:22Activation and Inactivation of G Proteins
Heterotrimeric G proteins are guanine nucleotide-binding proteins. As the name suggests, heterotrimeric G proteins are composed of three subunits: alpha, beta, and gamma. They remain GDP-bound or GTP-bound inside the cells and switch between inactive/active states. The Gα subunit possesses the nucleotide-binding pocket that binds guanine nucleotides and switches between GDP or GTP-bound states. In contrast, the Gꞵ and Gγ subunits are always bound together with high affinity and are together...
01:25Drug-Receptor Interaction: Agonist
Agonists are drugs that interact with specific receptors in the body to produce a biological response. When an agonist binds to a receptor, it activates or enhances the receptor's function, leading to physiological effects. The interaction between agonist drugs and receptors is crucial for their therapeutic action in various medical treatments.
Agonists can bind to receptors in different ways. Some agonists bind directly to the receptor's active site, mimicking the endogenous ligand's action.
Agonists can bind to receptors in different ways. Some agonists bind directly to the receptor's active site, mimicking the endogenous ligand's action.
01:31Adrenergic Receptors: ɑ Subtype
Adrenoceptors are classified into α and ꞵ classes based on their potencies to catecholamine agonists. α-adrenoceptors show the following order of catecholamine potency:
Adrenaline ≥ Noradrenaline >> Isoprenaline
α-adrenoceptors are further divided into α1 and α2-adrenoceptors.
α1-Adrenoceptors: These receptors are located postsynaptically on the effector organs and cause constriction of smooth muscle mediated by activation of phospholipase C—inositol-1,4,5-trisphosphate...
Adrenaline ≥ Noradrenaline >> Isoprenaline
α-adrenoceptors are further divided into α1 and α2-adrenoceptors.
α1-Adrenoceptors: These receptors are located postsynaptically on the effector organs and cause constriction of smooth muscle mediated by activation of phospholipase C—inositol-1,4,5-trisphosphate...
01:28Drug-Receptor Interaction: Antagonist
An antagonist is a drug that binds strongly to a receptor without activating it. An antagonist prevents other molecules, such as neurotransmitters or hormones, from binding to the receptor and triggering a cellular response. Such interaction effectively hinders the normal physiological processes mediated by the receptor, resulting in various pharmacological effects depending on the specific receptor targeted.
Antagonists can be classified as competitive or noncompetitive based on their...
Antagonists can be classified as competitive or noncompetitive based on their...
01:12GPCR Desensitization
G protein-coupled receptor (GPCR) signaling plays a crucial role in cell functioning. GPCR desensitization is an equally essential process. It allows cells to respond to changing environments and regain sensitivity to new stimuli while preventing unnecessary stimulation when no longer needed. Prolonged exposure to stimuli leads to GPCR desensitization. It involves blocking the receptors from binding and activating additional G proteins. This inhibits activation of downstream effectors, thereby...
01:09GPCRs Regulate Adenylyl Cylase Activity
Some GPCRs transmit signals through adenylyl cyclase (AC), a transmembrane enzyme. AC helps synthesize second messenger cyclic adenosine monophosphate (cAMP). AC catalyzes cyclization reaction and converts ATP to cAMP by releasing a pyrophosphate. The pyrophosphate is further hydrolyzed to phosphate by the enzyme pyrophosphatase, which drives cAMP synthesis to completion. However, cAMP is rapidly degraded to 5′ AMP by the enzymes phosphodiesterase (PDE), preventing overstimulation of cells.
Two...
Two...