Disease relevance of Kcnj8

• 60 min of myocardial regional ischemia followed by 24-72 h, but not 3-6 h, of reperfusion specifically upregulated Kir6.1 mRNA not only in the ischemic (approximately 2.7-3.1-fold) but also in the nonischemic (approximately 2.0-2.6-fold) region of the left ventricle [1].
• Thus, the stress-related induction of cardiac Kir6.1 mRNA and protein expression under myocardial ischemia is inhibited by pretreatment with an AT1 antagonist, but also in part by an ACE inhibitor, suggesting that activation of local renin-angiotensin system may play a role [2].
• A selective modulation of the Kir6.1 subunit in the cholinergic striatal interneurons may eventually be of therapeutic value for the treatment of Parkinson's disease [3].
• Here, we investigated the regulation of the two pore-forming channel proteins, Kir6.1 and Kir6.2, in response to hypoxia in vivo and in vitro [4].

High impact information on Kcnj8

• 24 h of continuous ischemia without reperfusion also induced an increase in Kir6.1 mRNA in both regions, whereas 15-30 min of ischemia followed by 24 h of reperfusion did not induce such expression [1].
• ATP-sensitive K(+) channels (K(ATP)) are an octameric complex of inwardly rectifying K(+) channels (Kir6.1 and Kir6.2) and sulfonylurea receptors (SUR1 and SUR2A/B), which are involved in several diseases [5].
• We have shown that maltose-binding fusion proteins (MBP) containing the COOH termini of K(ATP) channels (Kir1.1, Kir6.1, and Kir6.2) form functional tetramers that directly bind at least two ATP molecules with negative cooperativity [6].
• A(1)R agonist activation of CNT2 occurs in both hepatocytes and FAO cells, which express Kir6.1, Kir6.2, SUR1, SUR2A, and SUR2B mRNA channel subunits [7].
• Electrophysiological studies of uKATP-1 expressed in Xenopus laevis oocytes show that uKATP-1 is a weak rectifier and is blocked with Ba2+ ions [8].

Biological context of Kcnj8

• We have isolated a cDNA encoding a novel member (uKATP-1) of the inward rectifier K+ channel family from a rat pancreatic islet cDNA library [8].
• Gene expression of mesangial SUR2 and Kir6.1/2 was examined by reverse transcription polymerase chain reaction (RT-PCR) and Northern analysis [9].
• Complementary studies showed abundant gene expression of Kir6.1, thereby establishing gene expression of both components of KATP [9].
• RESULTS: Ketamine racemate inhibited the activities of the reassociated KATP channels in a SUR subtype-dependent manner: SUR2A/Kir6.2 (IC50 = 83 microM), SUR2B/Kir6.1 (IC50 = 77 microM), SUR2B/Kir6.2 (IC50 = 89 microM), and SUR1/Kir6.2 (IC50 = 1487 microM) [10].
• KATP channels are composed of an inwardly rectifying pore-forming unit (Kir6.1 or Kir6.2) and a sulfonylurea binding site [11].

Anatomical context of Kcnj8

• Single-channel patch clamp study of clonal human kidney epithelial cells (HEK293) transfected with uKATP-1 cDNA reveals that uKATP-1 closes in response to 1 mM ATP and has a single channel conductance of 70 +/- 2 picosiemens (n = 6), indicating that uKATP-1 is an ATP-sensitive inward rectifier K+ channel [8].
• Kir6.1 is the principal pore-forming subunit of astrocyte but not neuronal plasma membrane K-ATP channels [12].
• The identification of Kir6.1 as the principal pore-forming subunit of plasma membrane K-ATP channels in astrocytes suggests that these glial K-ATP channels act in synergy with neuronal Kir6.2-mediated K-ATP channels during metabolic challenges in the brain [12].
• This complete colocalization of the Kir6.1 subunit in cholinergic interneurons is interesting with respect to the pharmacological potential of these channels [3].
• In contrast, the Kir6.1 and SUR2B mRNAs were not seen in vena cava, other small veins, myocardium and skeletal muscles [13].

Associations of Kcnj8 with chemical compounds

• In addition, uKATP-1 is activated by the KATP channel opener, diazoxide [8].
• Except for rats pretreated with TCV-116, Kir6.1 mRNA levels were positively correlated with those for brain natriuretic peptide (BNP), a molecular indicator of regional wall stress, in both the non-ischemic and the ischemic regions [2].
• After fusion of nephron and CCD, Kir6.1 protein was restricted to the apical membrane of proximal tubule [14].
• Kir6.1/SUR2B may be the major potassium channels that mediate propionate-induced dilatation of the artery [15].
• Glucose-receptive neurones in the rat ventromedial hypothalamus express KATP channels composed of Kir6.1 and SUR1 subunits [16].

Other interactions of Kcnj8

• K-ATP channels consist of two structurally different subunits: a pore-forming subunit of the Kir6.0-family (Kir6.1 or Kir6.2) and a sulfonylurea receptor (SUR1, SUR2, SUR2A, SUR2B) with regulatory activity [17].
• However, there are no significant expression changes of Kir2.1, Kir3.1, Kir6.1, and Kir6.2 in diabetic rats [18].
• In vitro we describe neuronal and cardiac cell lines in which Kir6.1 is up-regulated by hypoxia, demonstrating that Kir6.1 is a hypoxia-inducible gene [4].
• We were able to record currents across the ZG membrane and, utilizing ion channel blockers, confirm the presence of the chloride channels CLC-2 and the potassium channel IRK-8 (Kir6.1), and additionally demonstrate the presence of a second chloride channel CLC-3 [19].

Analytical, diagnostic and therapeutic context of Kcnj8

• Here, using immunocytochemistry with monospecific antibodies against the Kir6.1 and Kir6.2 subunits, we analyze the regional and cellular distribution of both proteins in the adult rat brain [17].
• The Kir6.1-positive neurons in the striatum could be characterized as cholinergic interneurones, verified by immunofluorescence double staining [3].
• Expression of mRNA for SUR2B and Kir6.1 was detected, with the use of RT-PCR, in the cultured basilar arterial muscle cells [15].
• 2. According to the results of Western blot analysis, Kir6.1 was strongly expressed in mitochondrial and microsome fractions, and faintly expressed in cell membrane fraction, whereas Kir6.2 was mainly expressed in the microsome fraction and weakly in cell membrane and mitochondrial fractions [20].
• The Kir6.1/uK(ATP)-1, subunit of ATP-sensitive K(+) channels (K(ATP)), was localized in adult rat brain by in situ hybridization and immunohistochemistry [21].

References