The inhibition of Kir2.1 potassium channels depolarizes spinal microglial cells, reduces their proliferation, and attenuates neuropathic pain.

Spinal microglia change their phenotype and proliferate after nerve injury, contributing to neuropathic pain. For the first time, we have characterized the electrophysiological properties of microglia and the potential role of microglial potassium channels in the spared nerve injury (SNI) model of neuropathic pain. We observed a strong increase of inward currents restricted at 2 days after injury associated with hyperpolarization of the resting membrane potential (RMP) in microglial cells compared to later time-points and naive animals. We identified pharmacologically and genetically the current as being mediated by Kir2.1 ion channels whose expression at the cell membrane is increased 2 days after SNI. The inhibition of Kir2.1 with ML133 and siRNA reversed the RMP hyperpolarization and strongly reduced the currents of microglial cells 2 days after SNI. These electrophysiological changes occurred coincidentally to the peak of microglial proliferation following nerve injury. In vitro, ML133 drastically reduced the proliferation of BV2 microglial cell line after both 2 and 4 days in culture. In vivo, the intrathecal injection of ML133 significantly attenuated the proliferation of microglia and neuropathic pain behaviors after nerve injury. In summary, our data implicate Kir2.1-mediated microglial proliferation as an important therapeutic target in neuropathic pain.

KCNJ15 Expression and Malignant Behavior of Esophageal Squamous Cell Carcinoma.

BACKGROUND: We aimed to clarify the role of potassium voltage-gated channel subfamily J member 15 (KCNJ15) in esophageal squamous cell carcinoma (ESCC) cells and its potential as a prognosticator in ESCC patients. METHODS: KCNJ15 transcription levels were evaluated in 13 ESCC cell lines and polymerase chain reaction (PCR) array analysis was conducted to detect coordinately expressed genes with KCNJ15. The biological functions of KCNJ15 in cell invasion, proliferation, migration, and adhesion were validated through small interfering RNA-mediated knockdown experiments. Cell proliferation was further evaluated through the forced expression experiment. KCNJ15 expression was detected in 200 ESCC tissues by quantitative real-time reverse transcription PCR (qRT-PCR) and analyzed in 64 representative tissues by immunohistochemistry. Correlations between KCNJ15 expression levels and clinicopathological features were also analyzed. RESULTS: The KCNJ15 expression levels varied widely in ESCC cell lines and correlated with COL3A1, JAG1, and F11R. Knockdown of KCNJ15 expression significantly repressed cell invasion, proliferation, and migration of ESCC cells in vitro. Furthermore, overexpression of KCNJ15 resulted in increased cell proliferation. Patients were stratified using the cut-off value of KCNJ15 messenger RNA (mRNA) levels in 200 ESCC tissues using receiver operating characteristic curve analysis; the high KCNJ15 expression group had significantly shorter overall and disease-free survival times. In multivariable analysis, high expression of KCNJ15 was identified as an independent poor prognostic factor. Staining intensity of in situ KCNJ15 protein expression tended to be associated with KCNJ15 mRNA expression levels. CONCLUSIONS: KCNJ15 is involved in aggressive tumor phenotypes of ESCC cells and its tissue expression levels may be useful as a prognosticator of patients with ESCC.

A Soluble Epoxide Hydrolase Inhibitor Upregulated KCNJ12 and KCNIP2 by Downregulating MicroRNA-29 in a Mouse Model of Myocardial Infarction.

BACKGROUND: Soluble epoxide hydrolase inhibitors (sEHi) have anti-arrhythmic effects, and we previously found that the novel sEHi t-AUCB (trans-4[-4-(3-adamantan-1-yl-ureido)-cyclohexyloxy]-benzoic acid) significantly inhibited ventricular arrhythmias after myocardial infarction (MI). However, the mechanism is unknown. It's known that microRNA-29 (miR-29) participates in the occurrence of arrhythmias. In this study, we investigated whether sEHi t-AUCB was protective against ischemic arrhythmias by modulating miR-29 and its target genes KCNJ12 and KCNIP2. METHODS: Male 8-week-old C57BL/6 mice were divided into five groups and fed distilled water only or distilled water with t-AUCB of different dosages for seven days. Then, the mice underwent MI or sham surgery. The ischemic region of the myocardium was obtained 24 hours after MI to detect miR-29, KCNJ12, and KCNIP2 mRNA expression levels via real-time PCR and KCNJ12 and KCNIP2 protein expression levels via western blotting. RESULTS: MiR-29 expression levels were significantly increased in the ischemic region of MI mouse hearts and the mRNA and protein expression levels of its target genes KCNJ12 and KCNIP2 were significantly decreased. T-AUCB prevented these changes dose-dependently. CONCLUSION: The sEHi t-AUCB regulates the expression levels of miR-29 and its target genes KCNJ12 and KCNIP2, suggesting a possible mechanism for its potential therapeutic application in ischemic arrhythmia.

The expression, regulation, and function of Kir4.1 (Kcnj10) in the mammalian kidney.

Kir4.1 is an inwardly rectifying potassium (K(+)) channel and is expressed in the brain, inner ear, and kidney. In the kidney, Kir4.1 is expressed in the basolateral membrane of the late thick ascending limb (TAL), the distal convoluted tubule (DCT), and the connecting tubule (CNT)/cortical collecting duct (CCD). It plays a role in K(+) recycling across the basolateral membrane in corresponding nephron segments and in generating negative membrane potential. The renal phenotypes of the loss-function mutations of Kir4.1 include mild salt wasting, hypomagnesemia, hypokalemia, and metabolic alkalosis, suggesting that the disruption of Kir4.1 mainly impairs the transport in the DCT. Patch-clamp experiments and immunostaining demonstrate that Kir4.1 plays a predominant role in determining the basolateral K(+) conductance in the DCT. However, the function of Kir4.1 in the TAL and CNT/CCD is not essential, because K(+) channels other than Kir4.1 are also expressed. The downregulation of Kir4.1 in the DCT reduced basolateral chloride (Cl(-)) conductance, suppressed the expression of ste20 proline-alanine-rich kinase (SPAK), and decreased Na-Cl cotransporter (NCC) expression and activity. This suggests that Kir4.1 regulates NCC expression by the modulation of the Cl(-)-sensitive with-no-lysine kinase-SPAK pathway.

The inward rectifier potassium channel Kir2.1 is expressed in mouse neutrophils from bone marrow and liver.

Neutrophils are phagocytic cells that play a critical role in innate immunity by destroying bacterial pathogens. Channels belonging to the inward rectifier potassium channel subfamily 2 (Kir2 channels) have been described in other phagocytes (monocytes/macrophages and eosinophils) and in hematopoietic precursors of phagocytes. Their physiological function in these cells remains unclear, but some evidence suggests a role in growth factor-dependent proliferation and development. Expression of functional Kir2 channels has not been definitively demonstrated in mammalian neutrophils. Here, we show by RT-PCR that neutrophils from mouse bone marrow and liver express mRNA for the Kir2 subunit Kir2.1 but not for other subunits (Kir2.2, Kir2.3, and Kir2.4). In electrophysiological experiments, resting (unstimulated) neutrophils from mouse bone marrow and liver exhibit a constitutively active, external K(+)-dependent, strong inwardly rectifying current that constitutes the dominant current. The reversal potential is dependent on the external K(+) concentration in a Nernstian fashion, as expected for a K(+)-selective current. The current is not altered by changes in external or internal pH, and it is blocked by Ba(2+), Cs(+), and the Kir2-selective inhibitor ML133. The single-channel conductance is in agreement with previously reported values for Kir2.1 channels. These properties are characteristic of homomeric Kir2.1 channels. Current density in short-term cultures of bone marrow neutrophils is decreased in the absence of growth factors that are important for neutrophil proliferation [granulocyte colony-stimulating factor (G-CSF) and stem cell factor (SCF)]. These results demonstrate that mouse neutrophils express functional Kir2.1 channels and suggest that these channels may be important for neutrophil function, possibly in a growth factor-dependent manner.

Potassium channel KCNJ15 is required for histamine-stimulated gastric acid secretion.

Gastric acid secretion is mediated by the K(+)-dependent proton pump (H(+),K(+)-ATPase), which requires a continuous supply of K(+) at the luminal side of the apical membrane. Several K(+) channels are implicated in gastric acid secretion. However, the identity of the K(+) channel(s) responsible for apical K(+) supply is still elusive. Our previous studies have shown the translocation of KCNJ15 from cytoplasmic vesicles to the apical membrane on stimulation, indicating its involvement in gastric acid secretion. In this study, the stimulation associated trafficking of KCNJ15 was observed in a more native context with a live cell imaging system. KCNJ15 molecules in resting live cells were scattered in cytoplasm but exhibited apical localization after stimulation. Furthermore, knocking down KCNJ15 expression with a short hairpin RNA adenoviral construct abolished histamine-stimulated acid secretion in rabbit primary parietal cells. Moreover, KCNJ15, like H(+),K(+)-ATPase, was detected in all of the parietal cells by immunofluorescence staining, whereas only about half of the parietal cells were positive for KCNQ1 under the same condition. Consistently, the endogenous protein levels of KCNJ15, analyzed by Western blotting, were higher than those of KCNQ1 in the gastric mucosa of human, mouse, and rabbit. These results provide evidence for a major role of KCNJ15 in apical K(+) supply during stimulated acid secretion.

KCNJ1 inhibits tumor proliferation and metastasis and is a prognostic factor in clear cell renal cell carcinoma.

Potassium inwardly rectifying channel, subfamily J, member 1 (KCNJ1), as an ATP-dependent potassium channel, plays an essential role in potassium balance. KCNJ1 variation is associated with multiple diseases, such as antenatal Bartter syndrome and diabetes. However, the role of KCNJ1 in clear cell renal cell carcinoma (ccRCC) is still unknown. Here, we studied the expression and function of KCNJ1 in ccRCC. The expression of KCNJ1 was evaluated in ccRCC tissues and cell lines by quantitative real-time PCR (qRT-PCR), Western blot, and immunohistochemistry analysis. The relationship between KCNJ1 expression and clinicopathological characteristics was analyzed. p3xFLAG-CMV-14 vector containing KCNJ1 was constructed and used for transfecting ccRCC cell lines 786-O and Caki-2. The effects of KCNJ1 on cell proliferation, invasion, and apoptosis were detected in ccRCC cell lines using cell proliferation assay, transwell assay, and flow cytometry, respectively. We found that KCNJ1 was low-expressed in ccRCC tissues samples and cell lines, and its expression level was significantly associated with tumor pathology grade (P = 0.002) and clinical stage (P = 0.023). Furthermore, the KCNJ1 expression was a prognostic factor of ccRCC patient's survival (P = 0.033). The re-expression of KCNJ1 in 786-O and Caki-2 significantly inhibited cancer cell growth and invasion and promoted cancer cell apoptosis. Moreover, knockdown of KCNJ1 in HK-2 cells promoted cell proliferation. Collectively, these data highlight that KCNJ1, low-expressed in ccRCC and associated with poor prognosis, plays an important role in ccRCC cell growth and metastasis.

Retinal vasculopathy is reduced by dietary salt restriction: involvement of Glia, ENaCα, and the renin-angiotensin-aldosterone system.

OBJECTIVE: Neovascularization and vaso-obliteration are vision-threatening events that develop by interactions between retinal vascular and glial cells. A high-salt diet is causal in cardiovascular and renal disease, which is linked to modulation of the renin-angiotensin-aldosterone system. However, it is not known whether dietary salt influences retinal vasculopathy and if the renin-angiotensin-aldosterone system is involved. We examined whether a low-salt (LS) diet influenced vascular and glial cell injury and the renin-angiotensin-aldosterone system in ischemic retinopathy. APPROACH AND RESULTS: Pregnant Sprague Dawley rats were fed LS (0.03% NaCl) or normal salt (0.3% NaCl) diets, and ischemic retinopathy was induced in the offspring. An LS diet reduced retinal neovascularization and vaso-obliteration, the mRNA and protein levels of the angiogenic factors, vascular endothelial growth factor, and erythropoietin. Microglia, which influence vascular remodeling in ischemic retinopathy, were reduced by LS as was tumor necrosis factor-α. Macroglial Müller cells maintain the integrity of the blood-retinal barrier, and in ischemic retinopathy, LS reduced their gliosis and also vascular leakage. In retina, LS reduced mineralocorticoid receptor, angiotensin type 1 receptor, and renin mRNA levels, whereas, as expected, plasma levels of aldosterone and renin were increased. The aldosterone/mineralocorticoid receptor-sensitive epithelial sodium channel alpha (ENaCα), which is expressed in Müller cells, was increased in ischemic retinopathy and reduced by LS. In cultured Müller cells, high salt increased ENaCα, which was prevented by mineralocorticoid receptor and angiotensin type 1 receptor blockade. Conversely, LS reduced ENaCα, angiotensin type 1 receptor, and mineralocorticoid receptor expression. CONCLUSIONS: An LS diet reduced retinal vasculopathy, by modulating glial cell function and the retinal renin-angiotensin-aldosterone system.

Modulation of voltage-dependent and inward rectifier potassium channels by 15-epi-lipoxin-A4 in activated murine macrophages: implications in innate immunity.

Potassium channels modulate macrophage physiology. Blockade of voltage-dependent potassium channels (Kv) by specific antagonists decreases macrophage cytokine production and inhibits proliferation. In the presence of aspirin, acetylated cyclooxygenase-2 loses the activity required to synthesize PGs but maintains the oxygenase activity to produce 15R-HETE from arachidonate. This intermediate product is transformed via 5-LOX into epimeric lipoxins, termed 15-epi-lipoxins (15-epi-lipoxin A4 [e-LXA4]). Kv have been proposed as anti-inflammatory targets. Therefore, we studied the effects of e-LXA4 on signaling and on Kv and inward rectifier potassium channels (Kir) in mice bone marrow-derived macrophages (BMDM). Electrophysiological recordings were performed in these cells by the whole-cell patch-clamp technique. Treatment of BMDM with e-LXA4 inhibited LPS-dependent activation of NF-κB and IκB kinase ß activity, protected against LPS activation-dependent apoptosis, and enhanced the accumulation of the Nrf-2 transcription factor. Moreover, treatment of LPS-stimulated BMDM with e-LXA4 resulted in a rapid decrease of Kv currents, compatible with attenuation of the inflammatory response. Long-term treatment of LPS-stimulated BMDM with e-LXA4 significantly reverted LPS effects on Kv and Kir currents. Under these conditions, e-LXA4 decreased the calcium influx versus that observed in LPS-stimulated BMDM. These effects were partially mediated via the lipoxin receptor (ALX), because they were significantly reverted by a selective ALX receptor antagonist. We provide evidence for a new mechanism by which e-LXA4 contributes to inflammation resolution, consisting of the reversion of LPS effects on Kv and Kir currents in macrophages.

Valsartan Upregulates Kir2.1 in Rats Suffering from Myocardial Infarction via Casein Kinase 2.

PURPOSE: Myocardial infarction (MI) results in an increased susceptibility to ventricular arrhythmias, due in part to decreased inward-rectifier K+ current (IK1), which is mediated primarily by the Kir2.1 protein. The use of renin-angiotensin-aldosterone system antagonists is associated with a reduced incidence of ventricular arrhythmias. Casein kinase 2 (CK2) binds and phosphorylates SP1, a transcription factor of KCNJ2 that encodes Kir2.1. Whether valsartan represses CK2 activation to ameliorate IK1 remodeling following MI remains unclear. METHODS: Wistar rats suffering from MI received either valsartan or saline for 7 days. The protein levels of CK2 and Kir2.1 were each detected via a Western blot analysis. The mRNA levels of CK2 and Kir2.1 were each examined via quantitative real-time PCR. RESULTS: CK2 expression was higher at the infarct border; and was accompanied by a depressed IK1/Kir2.1 protein level. Additionally, CK2 overexpression suppressed KCNJ2/Kir2.1 expression. By contrast, CK2 inhibition enhanced KCNJ2/Kir2.1 expression, establishing that CK2 regulates KCNJ2 expression. Among the rats suffering from MI, valsartan reduced CK2 expression and increased Kir2.1 expression compared with the rats that received saline treatment. In vitro, hypoxia increased CK2 expression and valsartan inhibited CK2 expression. The over-expression of CK2 in cells treated with valsartan abrogated its beneficial effect on KCNJ2/Kir2.1. CONCLUSIONS: AT1 receptor antagonist valsartan reduces CK2 activation, increases Kir2.1 expression and thereby ameliorates IK1 remodeling after MI in the rat model.

Dynamic reciprocity of sodium and potassium channel expression in a macromolecular complex controls cardiac excitability and arrhythmia.

The cardiac electrical impulse depends on an orchestrated interplay of transmembrane ionic currents in myocardial cells. Two critical ionic current mechanisms are the inwardly rectifying potassium current (I(K1)), which is important for maintenance of the cell resting membrane potential, and the sodium current (I(Na)), which provides a rapid depolarizing current during the upstroke of the action potential. By controlling the resting membrane potential, I(K1) modifies sodium channel availability and therefore, cell excitability, action potential duration, and velocity of impulse propagation. Additionally, I(K1)-I(Na) interactions are key determinants of electrical rotor frequency responsible for abnormal, often lethal, cardiac reentrant activity. Here, we have used a multidisciplinary approach based on molecular and biochemical techniques, acute gene transfer or silencing, and electrophysiology to show that I(K1)-I(Na) interactions involve a reciprocal modulation of expression of their respective channel proteins (Kir2.1 and Na(V)1.5) within a macromolecular complex. Thus, an increase in functional expression of one channel reciprocally modulates the other to enhance cardiac excitability. The modulation is model-independent; it is demonstrable in myocytes isolated from mouse and rat hearts and with transgenic and adenoviral-mediated overexpression/silencing. We also show that the post synaptic density, discs large, and zonula occludens-1 (PDZ) domain protein SAP97 is a component of this macromolecular complex. We show that the interplay between Na(v)1.5 and Kir2.1 has electrophysiological consequences on the myocardium and that SAP97 may affect the integrity of this complex or the nature of Na(v)1.5-Kir2.1 interactions. The reciprocal modulation between Na(v)1.5 and Kir2.1 and the respective ionic currents should be important in the ability of the heart to undergo self-sustaining cardiac rhythm disturbances.

Oligodendrocyte precursor cells are accurate sensors of local K+ in mature gray matter.

Oligodendrocyte precursor cells (OPCs) are the major source of myelinating oligodendrocytes during development. These progenitors are highly abundant at birth and persist in the adult where they are distributed throughout the brain. The large abundance of OPCs after completion of myelination challenges their unique role as progenitors in the healthy adult brain. Here we show that adult OPCs of the barrel cortex sense fine extracellular K(+) increases generated by neuronal activity, a property commonly assigned to differentiated astrocytes rather than to progenitors. Biophysical, pharmacological, and single-cell RT-PCR analyses demonstrate that this ability of OPCs establishes itself progressively through the postnatal upregulation of Kir4.1 K(+) channels. In animals with advanced cortical myelination, extracellular stimulation of layer V axons induces slow K(+) currents in OPCs, which amplitude correlates with presynaptic action potential rate. Moreover, using paired recordings, we demonstrate that the discharge of a single neuron can be detected by nearby adult OPCs, indicating that these cells are strategically located to detect local changes in extracellular K(+) concentration during physiological neuronal activity. These results identify a novel unitary neuron-OPC connection, which transmission does not rely on neurotransmitter release and appears late in development. Beyond their abundance in the mature brain, the postnatal emergence of a physiological response of OPCs to neuronal network activity supports the view that in the adult these cells are not progenitors only.

Functional expression of a Kir2.1-like inwardly rectifying potassium channel in mouse mammary secretory cells.

K(+) channels in mammary secretory (MS) cells are believed to play a role in transcellular electrolyte transport and thus determining ionic composition of the aqueous phase of milk. However, direct evidence for specific K(+) channel activity in native MS cells is lacking at the single-cell level. Here, we show for the first time that an inwardly rectifying K(+) (Kir) channel is functionally expressed in fully differentiated MS cells that were freshly isolated from the mammary gland of lactating mice. Using the standard whole cell patch-clamp technique, we found that mouse MS cells consistently displayed a K(+) current, whose electrophysiological properties are similar to those previously reported for Kir2.x channels, particularly Kir2.1: 1) current-voltage relationship with strong inward rectification, 2) slope conductance approximately proportional to the square root of external K(+) concentration, 3) voltage- and time-dependent and high-affinity block by external Ba(2+), and 4) voltage-dependent inhibition by external Cs(+). Accordingly, RT-PCR analysis revealed the gene expression of Kir2.1, but not Kir2.2, Kir2.3, and Kir2.4, in lactating mouse mammary gland, and immunohistochemical staining showed Kir2.1 protein expression in the secretory cells. Cell-attached patch recordings from MS cells revealed that a 31-pS K(+) channel with strong inward rectification was likely active at the resting membrane potential. Collectively, the present work demonstrates that a functional Kir2.1-like channel is expressed in lactating mouse MS cells. We propose that the channel might be involved, at least in part, in secretion and/or preservation of ionic components of milk stored into the lumen of these cells.

Chronic opioids regulate KATP channel subunit Kir6.2 and carbonic anhydrase I and II expression in rat adrenal chromaffin cells via HIF-2α and protein kinase A.

At birth, asphyxial stressors such as hypoxia and hypercapnia are important physiological stimuli for adrenal catecholamine release that is critical for the proper transition to extrauterine life. We recently showed that chronic opioids blunt chemosensitivity of neonatal rat adrenomedullary chromaffin cells (AMCs) to hypoxia and hypercapnia. This blunting was attributable to increased ATP-sensitive K(+) (KATP) channel and decreased carbonic anhydrase (CA) I and II expression, respectively, and involved µ- and δ-opioid receptor signaling pathways. To address underlying molecular mechanisms, we first exposed an O2- and CO2-sensitive, immortalized rat chromaffin cell line (MAH cells) to combined µ {[d-Arg(2),Ly(4)]dermorphin-(1-4)-amide}- and δ ([d-Pen(2),5,P-Cl-Phe(4)]enkephalin)-opioid agonists (2 µM) for ∼7 days. Western blot and quantitative real-time PCR analysis revealed that chronic opioids increased KATP channel subunit Kir6.2 and decreased CAII expression; both effects were blocked by naloxone and were absent in hypoxia-inducible factor (HIF)-2α-deficient MAH cells. Chronic opioids also stimulated HIF-2α accumulation along a time course similar to Kir6.2. Chromatin immunoprecipitation assays on opioid-treated cells revealed the binding of HIF-2α to a hypoxia response element in the promoter region of the Kir6.2 gene. The opioid-induced regulation of Kir6.2 and CAII was dependent on protein kinase A, but not protein kinase C or calmodulin kinase, activity. Interestingly, a similar pattern of HIF-2α, Kir6.2, and CAII regulation (including downregulation of CAI) was replicated in chromaffin tissue obtained from rat pups born to dams exposed to morphine throughout gestation. Collectively, these data reveal novel mechanisms by which chronic opioids blunt asphyxial chemosensitivity in AMCs, thereby contributing to abnormal arousal responses in the offspring of opiate-addicted mothers.

A primary culture system of mouse thick ascending limb cells with preserved function and uromodulin processing.

The epithelial cells lining the thick ascending limb (TAL) of the loop of Henle perform essential transport processes and secrete uromodulin, the most abundant protein in normal urine. The lack of differentiated cell culture systems has hampered studies of TAL functions. Here, we report a method to generate differentiated primary cultures of TAL cells, developed from microdissected tubules obtained in mouse kidneys. The TAL tubules cultured on permeable filters formed polarized confluent monolayers in ∼12 days. The TAL cells remain differentiated and express functional markers such as uromodulin, NKCC2, and ROMK at the apical membrane. Electrophysiological measurements on primary TAL monolayers showed a lumen-positive transepithelial potential (+9.4 ± 0.8 mV/cm(2)) and transepithelial resistance similar to that recorded in vivo. The transepithelial potential is abolished by apical bumetanide and in primary cultures obtained from ROMK knockout mice. The processing, maturation and apical secretion of uromodulin by primary TAL cells is identical to that observed in vivo. The primary TAL cells respond appropriately to hypoxia, hypertonicity, and stimulation by desmopressin, and they can be transfected. The establishment of this primary culture system will allow the investigation of TAL cells obtained from genetically modified mouse models, providing a critical tool for understanding the role of that segment in health and disease.

Up-regulation of Kir2.1 (KCNJ2) by the serum & glucocorticoid inducible SGK3.

BACKGROUND/AIMS: The serum & glucocorticoid inducible kinase SGK3, an ubiquitously expressed serine/threonine kinase, regulates a variety of ion channels. It has previously been shown that SGK3 upregulates the outwardly rectifying K(+) channel KV11.1, which is expressed in cardiomyocytes. Cardiomyocytes further express the inward rectifier K(+) channel K(ir)2.1, which contributes to maintenance of resting cell membrane potential. Loss-of-function mutations of KCNJ2 encoding K(ir)2.1 result in Andersen-Tawil syndrome with periodic paralysis, cardiac arrhythmia and dysmorphic features. The present study explored whether SGK3 participates in the regulation of K(ir)2.1. METHODS: cRNA encoding K(ir)2.1 was injected into Xenopus oocytes with and without additional injection of cRNA encoding wild type SGK3, constitutively active (S419D)SGK3 or inactive (K191N)SGK3. Kir2.1 activity was determined by two-electrode voltage-clamp and K(ir)2.1 protein abundance in the cell membrane by immunostaining and subsequent confocal imaging or by chemiluminescence. RESULTS: Injection of 10 ng cRNA encoding wild type SGK3 and (S419D)SGK3, but not (K191N)SGK3 significantly enhanced K(ir)2.1-mediated currents. SGK inhibitor EMD638683 (50 µM) abrogated (S419D)SGK3-induced up-regulation of K(ir)2.1. Moreover, wild type SGK3 enhanced the channel protein abundance in the cell membrane. The decay of K(ir)2.1-mediated currents following inhibition of channel insertion into the cell membrane by brefeldin A (5 µM) was similar in oocytes coexpressing K(ir)2.1 and SGK3 as in oocytes expressing K(ir)2.1 alone, suggesting that SGK3 influences channel insertion into rather than channel retrieval from the cell membrane. CONCLUSIONS: SGK3 is a novel regulator of K(ir)2.1.

Gene expression and cellular localization of ROMKs in the gills and kidney of Mozambique tilapia acclimated to fresh water with high potassium concentration.

Regulation of plasma K(+) levels in narrow ranges is vital to vertebrate animals. Since seawater (SW) teleosts are loaded with excess K(+), they constantly excrete K(+) from the gills. However, the K(+) regulatory mechanisms in freshwater (FW)-acclimated teleosts are still unclear. We aimed to identify the possible K(+) regulatory mechanisms in the gills and kidney, the two major osmoregulatory organs, of FW-acclimated Mozambique tilapia (Oreochromis mossambicus). As a potential molecular candidate for renal K(+) handling, a putative renal outer medullary K(+) channel (ROMK) was cloned from the tilapia kidney and tentatively named "ROMKb"; another ROMK previously cloned from the tilapia gills was thus renamed "ROMKa". The fish were acclimated to control FW or to high-K(+) (H-K) FW for 1 wk, and we assessed physiological responses of tilapia to H-K treatment. As a result, urinary K(+) levels were slightly higher in H-K fish, implying a role of the kidney in K(+) excretion. However, the mRNA expression levels of both ROMKa and ROMKb were very low in the kidney, while that of K(+)/Cl(-) cotransporter 1 (KCC1) was robust. In the gills, ROMKa mRNA was markedly upregulated in H-K fish. Immunofluorescence staining showed that branchial ROMKa was expressed at the apical membrane of type I and type III ionocytes, and the ROMKa immunosignals were more intense in H-K fish than in control fish. The present study suggests that branchial ROMKa takes a central role for K(+) regulation in FW conditions and that K(+) excretion via the gills is activated irrespective of environmental salinity.

Kir6.2-containing ATP-sensitive K(+) channel is required for cardioprotection of resveratrol in mice.

BACKGROUND: Resveratrol is a natural compound that affects energy metabolism and is also known to possess an array of cardioprotective effects. However, its overall effects on energy metabolism and the underlying mechanism involved in cardioprotection require further investigation. Herein we hypothesize that ATP-sensitive potassium (K-ATP) channels as molecular sensors of cellular metabolism may mediate the cardioprotective effects of resveratrol. METHODS: Kir6.2 knockout, Kir6.1 heterozygous and wild-type (WT) mice were subjected to ischemia/reperfusion injury and were injected with resveratrol (10 mg/kg, i.p). Myocardial infarct size, serum lactate dehydrogenase (LDH) and creatine kinase (CK) activities were determined. Neonatal cardiomyocytes were used in in vitro assays to investigate the underlying mechanism of resveratrol in cardioprotection. RESULTS: Resveratrol treatment significantly reduced myocardial infarct size and serum LDH and CK activity and inhibited oxygen-glucose deprivation/reoxygenation - induced cardiomyocyte apoptosis in WT and Kir6.1 heterozygous mice, but Kir6.2 deficiency can abolish the cardioprotective effects of resveratrol in vivo and in vitro. We further found that resveratrol enhanced 5'-AMP-activated protein kinase (AMPK) phosphorylation and promoted the association of AMPK with Kir6.2. Suppression of AMPK attenuated and activation of AMPK mimicked the cardioprotective effects of resveratrol in cardiomyocytes. Notably, Kir6.2 knockout also reversed the cardioprotection of AMPK activator. CONCLUSIONS: Our study demonstrates that resveratrol exerts cardioprotective effects through AMPK -Kir6.2/K-ATP signal pathway and Kir6.2-containing K-ATP channel is required for cardioprotection of resveratrol.

The antiepileptic effect of the glycolytic inhibitor 2-deoxy-D-glucose is mediated by upregulation of K(ATP) channel subunits Kir6.1 and Kir6.2.

Metabolic modulation of neuronal excitability is becoming increasingly important as an antiepileptic therapy. It was reported that the glycolytic inhibitor 2-deoxy-D-glucose (2-DG) and the activation of the ATP-sensitive potassium ion channel (K(ATP) channel) had an antiepileptic effect in models of epilepsy. To explore whether 2-DG exerts an antiepileptic effect through upregulation of the K(ATP) channel subunits Kir6.1 and Kir6.2, the expression of these subunits in hippocampus of five groups of mice with pilocarpine-induced status epilepticus (SE) was evaluated. A seizure group with pilocarpine-kindling convulsions (EP) was compared to similar groups treated with high, medium, and low 2-DG concentrations (100-500 mg/kg) and a normal control group (Con). Kir6.1 and Kir6.2 mRNAs and proteins were analyzed at 4 h, 1 days (acute period), 7 days (latent period), 30, and 60 days (chronic period) following SE. In the seizure group (compared to the Con group), hippocampal expression of Kir6.1 and Kir6.2 increased dramatically at 1, 7, and 30 days, and was further increased after treatment with medium and high dose 2-DG (all P < 0.05). Our results suggest that 2-DG may exert an antiepileptic effect through up-regulation of mRNAs and protein levels of Kir6.1 and Kir6.2, which may therefore be used as molecular targets in the treatment of epilepsy with 2-DG.