GIRk Assays
Background of Girk
G protein-gated inwardly-rectifying potassium (Girk) channel, also known as the Kir3 channel, is an important rectifier structural unit of the G protein-coupled receptor-mediated signaling pathway. Its main function is a property called inward rectification. It modulates the excitability of cells in the brain and provides a therapeutic target for a variety of neurological or cardiac diseases.
Fig.1. Structure Prediction of the Human Girk 2. (Uniprot ID P48051; obtained from Alphafold)
Distributions and Functions of GIRK
The Girk channel is mainly distributed in the brain and heart and modulates the resting membrane potential of certain types of cells in these two regions. It is better at conducting K+ into the cell than outside the cell, this ability is called inward rectification. The signals initiated by the Girk channel are involved in vital activities such as pain perception, emotional cognition, and heart rate regulation.
Submembers and Mechanisms of Girk
Girk channels are tetramers formed by four subunits coded by four genes.
| Channel | Gene | Mechanism | Activator | Blocker |
| Girk.1 | KCNJ3 |
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| Girk.2 | KCNJ6 |
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| Girk.3 | KCNJ9 | |||
| Girk.4 | KCNJ5 |
Assay List of GIRK Channel
Creative Biolabs can provide a range of assays of GIRK channels. You can choose the assay in the list or contact us for more information:
Published Data
| Paper Title | Molecular basis of signaling specificity between GIRK channels and GPCRs |
| Journal | eLife |
| Published | 2018 |
| Abstract | Heart rate is tightly regulated by the sympathetic and parasympathetic branches of the autonomic nervous system, which control heart rate by stimulating different GPCR receptors and exciting the electrical properties of cardiac pacemaker cells. In this process, the parasympathetic nerve slows the heart rate by activating the inhibitory G protein (Gαi) muscarinic acetylcholine receptors M2 (M2Rs). GTP-bound Gα (Gαi (GTP)) promotes the free diffusion of Gβγ subunits to the surface of the inner membrane, opens GIRK channels, and hyperpolarizes the membrane, thereby slowing the heart rate. Conversely, sympathetic stimulation also releases Gβγ subunits through Gαs, but this process does not result in the opening of GIRK channels. This difference is named the Gβγ-specific puzzle of the GIRK pathway. Although there are several possible hypotheses for this issue, the lack of sufficient experimental data and theoretical support still makes this issue endlessly debated. This study explores this question with a simple biochemical solution, backed by actionable data. |
| Result |
In this study, bioluminescence resonance energy transfer experiments with real-time detection of labeled protein products and currents explored and resolved the underlying mechanism of this specificity of M2R activation of GIRK. Data suggest that M2Rs catalyze the release of Gβγ subunits at a much higher rate than the rate at which subunits are generated by the b2Ars pathway, which leads to concentration-dependent activation of GIRK and regulation of subsequent other targets. The Gαs (GTP) concentration produced by the β2AR pathway was apparently sufficient to stimulate downstream amplified Gas pathways and increase heart rate, but the lower Gβγ levels produced were unable to fully activate GIRK. Gene overexpression experiments also confirmed this hypothesis. In subsequent studies, it was proved that the reason for the higher release rate of Gβγ catalyzed by the M2R pathway is because the association rate of G protein trimer is higher and the binding speed is faster. Overall, the researchers accounted for specificity by rate differences in individual kinetic steps and marked activation of GIRK as concentration-dependent.
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Fig.2. Gβγ specificity between GPCRs and GIRK channels. (Touhara, 2018)
Reference
- Touhara, K.T.; et al. Molecular basis of signaling specificity between GIRK channels and GPCRs. eLife. 2018, 7: e42908.
