G-protein gated inwardly rectifying K-channel 4

Alternate Nomenclature: NP_000881, Heart KATP channel, CIR, Kir3.4. K-channel, inwardly rectifying subfamily J member 5.

G protein-gated inwardly rectifying potassium (GIRK) channels hyperpolarize neurons in response to activation of many G-protein coupled receptors and control the excitability of neurons at post synaptic terminals through GIRK-mediated self-inhibition, slow synaptic potentials and volume transmission. GIRK channel functioning and trafficking are highly dependent on their subunit composition. GIRK activity has an important role in physiological responses, including pain perception and memory modulation. Abnormal GIRK function has been implicated in altering neuronal excitability and cell death that may be important in the pathophysiology of human diseases such as epilepsy, Down’s syndrome, Parkinson’s disease and drug addiction.(1). GIRK channels are expressed in the brain, heart, skeletal muscle, and endocrine tissue. GIRK channels are members of the super-family of proteins known as inward rectifier K+ (Kir) channels that function to stabilize the cell resting membrane potential near the K+ equilibrium potential (EK). These channels generate slow inhibitory postsynaptic potentials following the activation of Gi/o-protein-coupled receptors .The major role of the GIRK channels is to mediate inhibitory responses in the nervous system by decreasing neuronal excitability. GIRK channels also play role at presynaptic sites due to their localization in axon terminals. A major G protein-coupled receptor activating postsynaptic GIRK channels is the metabotropic γ-aminobutyric acid (_B) (GABA_B) receptor. GIRK channel-mediated inhibition of glutamate release occurs through GABA_B receptors in the cerebral cortex. Four different cDNAs encode GIRK channel subunits in mammals (GIRK1–4) and they combine to form functional homomeric as well as heteromeric channels. In central neurons most neuronal GIRK channels are heteromeric complexes containing both GIRK1 and GIRK2. (2).

GIRK4 channels are expressed mainly in the heart, and contribute to physiological vagal bradycardia in atrial myocytes by activation of parasympathetic muscarinic M2 acetylcholine receptor and provides cardio protection during myocardial ischemia. These channels are activated by direct interaction from pertussis toxin (PTX)-sensitive heterotrimeric G-protein coupled receptors (GPCRs)(3) .Tachycardia in response to increased sympathetic tone would be counteracted by simultaneous GIRK channel activation. Agonist stimulation of G-protein-coupled receptors (GPCRs) leads to numerous cellular responses via activation of heterotrimeric G-proteins and thereby modulation of downstream signaling components. In atrial and nodal cardiac myocytes binding of acetylcholine to M2 muscarinic receptors activates inhibitory G-proteins, which in turn stimulate GIRK through direct binding of the Gβγ subunit(4). Congenital long QT syndrome (LQTS) is an inherited cardiac disorder associated with a prolonged QT interval on surface electrocardiogram occurs due to mutation in GIRK4, encoded by the KCNJ5 gene, as it leads to ion defect in channel trafficking and a reduction in the Potassium current.(5) Adenosine (Ado) or Ado receptor agonists can cause a reduction in the infarct size or an improvement in left ventricular function when given during reperfusion or during both low-flow ischemia and reperfusion in the isolated and perfused heart. The protective effect of Adenosine in the intact heart is mediated by Adenosine receptors.A1 adenosine receptor(A1AdoR) hyperpolarizes the membrane potential and decreases the action potential duration mediated by GIRK4 (6).

The GIRK4-selective antibodies were generated using a peptide selected form a region between amino acids 369-389.  The GIRK4 antibodies are affinity purified over immobilized antigen based affinity chromatography, and the purified immunoglobulins are stabilized in antibody stabilization buffer for long-term storage.  FabGennix Int. Inc. will provide limited quantities of antigenic blocking peptides for competition assays involving GIRK4 antibody. Antibodies to GIRK4 label ~49kDa protein in Western blot positive control and several other tissues.  FabGennix Inc. will conjugate this and other antibodies from its catalog to either secondary enzymes (alk-Pase or HRP) or fluorescent probes at a nominal cost upon request.  FabGennix also provides custom antibody production services for researchers that are looking for high affinity mono and polylconal antibodies in various species. We specialize in making application specific antibodies that are useful in IHC, confocal and other applications where native antigen is detected. For a complete listing of all FabGennix antibodies please visit www.Fabgennix.com.

Immunogen:            Synthetic peptide from amino acids 369-389 corresponding human GIRK4 protein from the following sequence (EMKREGRLLQYLPSPPLLGGC), was selected from the unique region of human GIRK2, peptide was post-synthetically modified to achieve highest antigenicity before used for coupling to KLH  using heterobifunctional cross linker for immunogen preparation. 

Concentration:         GIRK4-401AP and GIRK3-FITC   Ig concentration 0.53-0.57 mg/ml in antibody stabilization buffer. 

Applications:        Antibody GIRK4-401AP is ideal for IMM/WB applications for detection of endogenous GIRK4 protein in PC-GIRK4 samples.  The dilutions for this antibody is for reference only, investigators are expected to determine the optimal conditions.    Western blotting: > 1:250; IMM:   Immunprecipitation1:200 recommended; IHC = nd.  Investigators who want to use this antibody in applications not listed here can ask for a complimentary sample of  GIRK2 antibodies.  We will be happy to provide this antibody form multiple rabbits.           

Reactivity:                This antibody detects a band of approximately 49kDa GIRK4 protein in PC-GIRK4 samples and a 49kDa protein in rat hippocampal samples.

Protocols:            Standard protocol for various applications (WB; I  MM and IHC) of this antibody is provided with the product specification sheet, however, FabGennix Inc.  strongly recommends investigators to optimize conditions for use of this antibody in their laboratories. 

 

For research use only, not for diagnostic or therapeutic use.