• The Korean Journal of Physiology and Pharmacology
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• v.5 no.5
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• pp.433-441
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• 2001

The ATP-sensitive potassium $(K_{ATP})$) channel is a member of inward rectifier potassium channel (Kir) that is inhibited by intracellular ATP and functions in close relation to sulfonylurea receptors (SUR). Although the molecular mechanism and physiological function of $K_{ATP}$ channels are well understood, the expression pattern during development or treatment with the channel modulators such as glybenclamide is little known. In this work, we determined mRNA levels of a $K_{ATP}$ channel (Kir6.2) and a sulfonylurea receptor (SUR2) in rat tissues by RNase protection assay. Levels of Kir6.2 and SUR2 mRNA in the rat brain and skeletal muscle were higher in adult $(90{\sim}120\;days)$ than in neonate $(2{\sim}8\;days),$ whereas those in the heart were not much different between neonate $(2{\sim}8\;days)$ and adult $(90{\sim}120\;days).$ In addition, none of $K_{ATP}$ channel modulators (opener, pinacidil and nicorandil; blocker, glybenclamide) affected the Kir6.2 mRNA levels in the heart, brain and skeletal muscle. The results indicate that the expression of Kir and SUR genes can vary age-dependently, but the expression of Kir is not dependent on the long-term treatment of channel modulators. The effect of the channel modulators on mRNA level of SUR is remained to be studied further.

• Genomics & Informatics
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• v.12 no.4
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• pp.283-288
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• 2014

Among all serious diseases globally, diabetes (type 1 and type 2) still poses a major challenge to the world population. Several target proteins have been identified, and the etiology causing diabetes has been reasonably well studied. But, there is still a gap in deciding on the choice of a drug, especially when the target is mutated. Mutations in the KCNJ11 gene, encoding the kir6.2 channel, are reported to be associated with congenital hyperinsulinism, having a major impact in causing type 1 diabetes, and due to the lack of its 3D structure, an attempt has been made to predict the structure of kir6.2, applying fold recognition methods. The current work is intended to investigate the affinity of four phytochemicals namely, curcumin (Curcuma longa), genistein (Genista tinctoria), piperine (Piper nigrum), and pterostilbene (Vitis vinifera) in a normal as well as in a mutant kir6.2 model by adopting a molecular docking methodology. The phytochemicals were docked in both wild and mutated kir6.2 models in two rounds: blind docking followed by ATP-binding pocket-specific docking. From the binding pockets, the common interacting amino acid residues participating strongly within the binding pocket were identified and compared. From the study, we conclude that these phytochemicals have strong affinity in both the normal and mutant kir6.2 model. This work would be helpful for further study of the phytochemicals above for the treatment of type 1 diabetes by targeting the kir6.2 channel.

• The Korean Journal of Physiology and Pharmacology
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• v.10 no.4
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• pp.199-205
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• 2006

The functional expression of potassium $(K^+)$ channels has electrophysiologically been studied in bone cells from several species, however, their identity and regulation of gene expressions in bone cells are not well known. In the present study, to investigate how $K^+$ channel expressions are regulated by estrogen, we measured changes of transcript levels of various $Ca^{2+}$-activated ($K_{Ca}$) and ATP-sensitive $K^+$ channels in rat osteoblastic ROS 17/2.8 cells after treatment with estrogen. Application of 17${\beta}$-estradiol $(E_2)$ for 24 h and 48 h increased mRNA and protein expressions of inwardly rectifying $K^+$ channel (Kir) 6.2 and type 2 small conductance $K_{Ca}$ channel (SK2), respectively. Combined treatment of cells with 17${\beta}-E_2$ and ICI 182,780, a pure antiestrogen, suppressed 17${\beta}-E_2$-induced alterations of SK2 and Kir6.2 mRNA levels. In addition, treatment of cells with U0126, a specific inhibitor of extracellular receptor kinases (ERK)1/2, and SP600125, a specific inhibitor of c-jun N-terminal kinase (JNK) blocked the enhancing effects of 17${\beta}-E_2$ on SK2 and Kir6.2 protein expressions. On the other hand, blocking of p38 mitogen-activated protein kinase had no effect. Taken together, these results indicate that 17${\beta}-E_2$ modulates SK2 and Kir6.2 expressions through the estrogen receptor, involving ERK1/2 and JNK activations.

• The Korean Journal of Physiology and Pharmacology
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• v.22 no.6
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• pp.697-703
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• 2018

Myoblast fusion depends on mitochondrial integrity and intracellular $Ca^{2+}$ signaling regulated by various ion channels. In this study, we investigated the ionic currents associated with $[Ca^{2+}]_i$ regulation in normal and mitochondrial DNA-depleted(${\rho}0$) L6 myoblasts. The ${\rho}0$ myoblasts showed impaired myotube formation. The inwardly rectifying $K^+$ current ($I_{Kir}$) was largely decreased with reduced expression of KIR2.1, whereas the voltage-operated $Ca^{2+}$ channel and $Ca^{2+}$-activated $K^+$ channel currents were intact. Sustained inhibition of mitochondrial electron transport by antimycin A treatment (24 h) also decreased the $I_{Kir}$. The ${\rho}0$ myoblasts showed depolarized resting membrane potential and higher basal $[Ca^{2+}]_i$. Our results demonstrated the specific downregulation of $I_{Kir}$ by dysfunctional mitochondria. The resultant depolarization and altered $Ca^{2+}$ signaling might be associated with impaired myoblast fusion in ${\rho}0$ myoblasts.

• Parasites, Hosts and Diseases
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• v.41 no.2
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• pp.129-133
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• 2003

A complete cDNA sequence encoding a pore-forming subunit (Kir6.2) of ATP-senstive potassium channel in the adult worm, Clonorchis sinensis, termed CsKir6.2, was isolated from an adult CDNA library. The cDNA contained a single open-reading frame of 333 amino acids, which has a structural motif (a GFG-motif) of the putative pore-forming loop of the Kir6.2. Peculiarly, the Cskir6.2 shows a lack-sequence structure, which deleted 57 amino acids were deleted from its N-terminus. The predicted amino acid sequence revealed a highly conserved sequence as other known other Kir6.2 subunits. The mRNA was weekly expressed in the adult worm.

• The Korean Journal of Physiology and Pharmacology
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• v.25 no.6
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• pp.565-574
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• 2021

Astrocytes are activated in response to brain damage. Here, we found that expression of Kir4.1, a major potassium channel in astrocytes, is increased in activated astrocytes in the injured brain together with upregulation of the neural stem cell markers, Sox2 and Nestin. Expression of Kir4.1 was also increased together with that of Nestin and Sox2 in neurospheres formed from dissociated P7 mouse brains. Using the Kir4.1 blocker BaCl₂ to determine whether Kir4.1 is involved in acquisition of stemness, we found that inhibition of Kir4.1 activity caused a concentration-dependent increase in sphere size and Sox2 levels, but had little effect on Nestin levels. Moreover, induction of differentiation of cultured neural stem cells by withdrawing epidermal growth factor and fibroblast growth factor from the culture medium caused a sharp initial increase in Kir4.1 expression followed by a decrease, whereas Sox2 and Nestin levels continuously decreased. Inhibition of Kir4.1 had no effect on expression levels of Sox2 or Nestin, or the astrocyte and neuron markers glial fibrillary acidic protein and β-tubulin III, respectively. Taken together, these results indicate that Kir4.1 may control gain of stemness but not differentiation of stem cells.

• The Korean Journal of Physiology and Pharmacology
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• v.5 no.2
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• pp.157-163
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• 2001

The effects of dimethyl sulfoxide (DMSO) were studied in two groups of Xenopus oocytes, one expressing ATP sensitive $K^+\;(K_{ATP})$ channel comprised of sulfonylurea receptor SUR1 and inwardly rectifying $K^+$ channel subunit Kir6.2, and the other expressing renal $K_{ATP}$ channel ROMK2. At concentrations of $0.3{\sim}10%$ (vol/vol) DMSO inhibited whole cell Kir6.2/SUR1 currents elicited by bath application of sodium azide (3 mM) in a concentration-dependent manner. The inhibition constant and Hill coefficient were 2.93% and 1.62, respectively. ROMK2 currents, however, was not affected significantly by DMSO. The results support the idea that DMSO inhibits $K_{ATP}$ channel expressed in Xenopus oocyte through a protein-specific mechanism(s) that remains to be further elucidated.

• The Korean Journal of Physiology and Pharmacology
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• v.7 no.3
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• pp.131-142
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• 2003

We have studied mutant forms of Kir2.1 in which an aspartate residue (D172), important for gating by intracellular polyamines, is replaced by one of three basic residues (Arg, Lys or His). Such channels are highly selective for $K^+$, but show inward rectification that is a shallow function of voltage compared with that found in wild type. This inward rectification occurs with a reduced affinity for spermine and persists in the absence of polyamines. Though the unitary current-voltage relation shows some inward rectification, it is insufficient to account for that seen under whole cell recording. Channels open and shut under single channel recording, and changes of $P_{open}$ appear to generate inward rectification. In D172H, the reduction in affinity for spermine is greater when His is protonated at low $pH_i$. The effective valency for spermine is reduced from $3.09{\pm}0.07$ in wild type to $1.95{\pm}0.09$ in D172H at $pH_i$ 6.3. In the presence of dual mutants of Kir2.1, where E224 is also replaced, spermine affinity becomes undetectable. However, channels still show inward rectification and open and shut under hyper- and depolarisation, respectively. We suggest that Kir2.1 channel are able to undergo conformation changes; these changes may be important physiologically in generating inward rectification, the normal parameters of which are set by the binding of polyamines such as spermine.

• Journal of Life Science
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• v.20 no.3
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• pp.457-461
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• 2010

Familial hypokalemic periodic paralysis (HOKPP) is an autosomal dominant disorder characterized by reversible flaccid paralysis and intermittent hypokalemia. Although it has been reported that decreased activity in the $K_{ATP}$ channels of the skeletal muscle cell membrane plays a role in the pathogenesis of HOKPP, a clear mechanism has not yet been established. This study aimed to investigate the molecular biological mechanism underlying the decreased activity of $K_{ATP}$ channels in the skeletal muscles of familial HOKPP patients by studying the levels of the $K_{ATP}$ channel subunit Kir6.2. We found that when cells obtained from healthy individuals (normal cells) and HOKPP patients (patient cells) were treated with 4 mM potassium buffer, there was no quantitative change in the KCNJ11 mRNA levels and no difference in the Kir6.2 protein expression in the cytosol and cell membrane. On the other hand, when 1 mM potassium buffer was used, normal cells showed decreased expression of KCNJ11 mRNA as well as decreased expression of Kir6.2 protein in the cell membrane. However, patient cells treated with the same buffer showed no quantitative change in the levels of KCNJ11 mRNA or in the levels of Kir6.2 protein in the cytosol and cell membrane. Thus, in HOKPP patients, the Kir6.2 protein cannot be transported from the cell membrane to the cytosol, leading to closure of the $K_{ATP}$ channels, induction of depolarization, and subsequently, to the paralytic symptoms observed in the patient. Our findings thus provide new insights into the pathogenesis of HOKPP.

• Neonatal Medicine
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• v.28 no.2
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• pp.94-98
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• 2021

Neonatal diabetes mellitus (NDM) is a rare disease that occurs at less than 6 months of age and is presumably caused by a mutation in the gene that affects pancreatic beta-cell function. Approximately 80% of NDM cases reveal a known genetic mutation, and mutations in potassium inwardly rectifying channel subfamily J member 11 (KCNJ11) and ABCC8 affecting the pancreatic beta-cell adenosine triphosphate-sensitive potassium channel may be treated with oral sulfonylurea. Early recognition of mutations in KCNJ11 and ABCC8 is important because early administration of sulfonylurea can not only control blood glucose levels but also improve neurodevelopmental outcomes. In the present study, we report a case of NDM that initially presented as diabetic ketoacidosis at the age of 1 month, accompanied by seizures during hospitalization. After confirmation of the KCNJ11 gene mutation (c.989A>C), we started administering oral sulfonylurea (glimepiride) at the age of 2 months. After gradually increasing the dosage of glimepiride, insulin was discontinued at the age of 3 months. To date, the infant's blood glucose levels have been well controlled without significant hypoglycemic events. No further episodes of seizures have occurred, and his developmental status is favorable.