G-protein activated inward rectifier potassium channel activity

Definition

Target type: molecularfunction

Enables the transmembrane transfer of a potassium ion by an inwardly-rectifying voltage-gated channel, where the inward rectification is due to a voltage-dependent block of the channel pore by a G protein. An inwardly rectifying current-voltage relation is one where at any given driving force the inward flow of K+ ions exceeds the outward flow for the opposite driving force. [GOC:cb, GOC:mah]

G-protein activated inward rectifier potassium (GIRK) channels are members of the inwardly rectifying potassium channel family. They are characterized by their high permeability to potassium ions and their inward rectification property, meaning that they conduct potassium ions more easily when the membrane potential is negative than when it is positive. GIRK channels are activated by the binding of G protein alpha subunits, specifically Gαi/o subunits, which are released from heterotrimeric G proteins upon activation of G protein-coupled receptors (GPCRs).

The molecular mechanism of GIRK channel activation involves a series of steps:

1. **GPCR activation:** Upon binding of a ligand, GPCRs undergo conformational changes that activate their associated G proteins.
2. **G protein activation:** The activated GPCR catalyzes the exchange of GDP for GTP on the alpha subunit of the G protein. This causes the Gα subunit to dissociate from the Gβγ dimer.
3. **GIRK channel activation:** The Gαi/o subunit binds to the GIRK channel, inducing a conformational change that opens the channel pore.

GIRK channels are important regulators of neuronal excitability, cardiac function, and other physiological processes. They contribute to the hyperpolarization of cells, which can suppress neuronal firing or slow heart rate.

Specifically, GIRK channels play a crucial role in:

* **Neurotransmission:** They mediate inhibitory postsynaptic potentials (IPSPs) in the nervous system by hyperpolarizing neurons, reducing their likelihood of firing.
* **Cardiac function:** They regulate heart rate by contributing to the hyperpolarization of pacemaker cells, which slows down the rate of depolarization and thus heart rate.
* **Smooth muscle relaxation:** They contribute to the relaxation of smooth muscle cells, such as those in the gastrointestinal tract and blood vessels.

In summary, GIRK channels are important regulators of cellular excitability and physiological processes. Their activation by G proteins through a series of molecular steps results in the opening of the channel pore and the influx of potassium ions, leading to hyperpolarization of the cell. This hyperpolarization can then have a range of effects on cell function, depending on the specific tissue and context.'
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Proteins (3)

Compounds (6)