Expression Of Voltage-gated Potassium Channels Research Articles

Ouabain-Induced Changes in the Expression of Voltage-Gated Potassium Channels in Epithelial Cells Depend on Cell-Cell Contacts.

Ouabain is a cardiac glycoside, initially isolated from plants, and currently thought to be a hormone since some mammals synthesize it endogenously. It has been shown that in epithelial cells, it induces changes in properties and components related to apical-basolateral polarity and cell-cell contacts. In this work, we used a whole-cell patch clamp to test whether ouabain affects the properties of the voltage-gated potassium currents (Ik) of epithelial cells (MDCK). We found that: (1) in cells arranged as mature monolayers, ouabain induced changes in the properties of Ik; (2) it also accelerated the recovery of Ik in cells previously trypsinized and re-seeded at confluence; (3) in cell-cell contact-lacking cells, ouabain did not produce a significant change; (4) Na+/K+ ATPase might be the receptor that mediates the effect of ouabain on Ik; (5) the ouabain-induced changes in Ik required the synthesis of new nucleotides and proteins, as well as Golgi processing and exocytosis, as evidenced by treatment with drugs inhibiting those processes; and (5) the signaling cascade included the participation of cSrC, PI3K, Erk1/2, NF-κB and β-catenin. These results reveal a new role for ouabain as a modulator of the expression of voltage-gated potassium channels, which require cells to be in contact with themselves.

C-X-C motif chemokine ligand 1 and its receptor C-X-C motif chemokine receptor 2 in trigeminal ganglion contribute to nerve injury-induced orofacial mechanical allodynia.

Orofacial ectopic pain induced by trigeminal nerve injury is a serious complication of dental treatment. C-X-C motif chemokine ligand 1 (CXCL1) and its primary receptor C-X-C motif chemokine receptor 2 (CXCR2) contribute to the development and maintenance of neuropathic pain in the spinal nervous system, but their roles in trigeminal neuropathic sensation are still poorly understood. This study aimed to investigate the exact role of CXCL1 and CXCR2 in the regulation of orofacial ectopic mechanical allodynia and their potential downstream mechanisms in the trigeminal ganglion (TG). The head withdrawal threshold (HWT) of C57BL/6mice was evaluated after inferior alveolar nerve (IAN) transection (IANX). Then, the distribution and expression of CXCL1 and CXCR2, and their potential downstream mechanisms in the TG were further measured using immunohistochemistry, real-time reverse transcription-quantitative polymerase chain reaction and Western blotting. Moreover, the effect of SB225002 (an inhibitor of CXCR2) on mechanical allodynia was examined. The data were analysed using the Student's t test and a analysis of variance (ANOVA). IANX triggered persistent (>21days) mechanical allodynia and upregulation of CXCL1 and CXCR2 in the TG. In addition, exogenous CXCL1 also lowered the HWT, which was alleviated by CXCR2 and protein kinase C (PKC) antagonists (p<.05). In addition, IANX increased the phosphorylated PKC (p-PKC) levels and decreased the expression of voltage-gated potassium channels (Kv), and these effects were reversed by inhibition of CXCR2 (p<.05). Our results demonstrated that CXCR2 participated in orofacial ectopic mechanical allodynia via downregulation of Kv1.4 and Kv1.1 through the PKC signalling pathway. This mechanism may be a potential target in developing a treatment strategy for ectopic orofacial pain.

IL-18 mediates sickle cell cardiomyopathy and ventricular arrhythmias

Previous reports indicate that IL18 is a novel candidate gene for diastolic dysfunction in sickle cell disease (SCD)–related cardiomyopathy. We hypothesize that interleukin-18 (IL-18) mediates the development of cardiomyopathy and ventricular tachycardia (VT) in SCD. Compared with control mice, a humanized mouse model of SCD exhibited increased cardiac fibrosis, prolonged duration of action potential, higher VT inducibility in vivo, higher cardiac NF-κB phosphorylation, and higher circulating IL-18 levels, as well as reduced voltage-gated potassium channel expression, which translates to reduced transient outward potassium current (Ito) in isolated cardiomyocytes. Administering IL-18 to isolated mouse hearts resulted in VT originating from the right ventricle and further reduced Ito in SCD mouse cardiomyocytes. Sustained IL-18 inhibition via IL-18–binding protein resulted in decreased cardiac fibrosis and NF-κB phosphorylation, improved diastolic function, normalized electrical remodeling, and attenuated IL-18–mediated VT in SCD mice. Patients with SCD and either myocardial fibrosis or increased QTc displayed greater IL18 gene expression in peripheral blood mononuclear cells (PBMCs), and QTc was strongly correlated with plasma IL-18 levels. PBMC-derived IL18 gene expression was increased in patients who did not survive compared with those who did. IL-18 is a mediator of sickle cell cardiomyopathy and VT in mice and a novel therapeutic target in patients at risk for sudden death.

KCND2 upregulation might be an independent indicator of poor survival in gastric cancer.

We aimed to investigate the expression of voltage-gated potassium channels KCND1/KCND2/KCND3 in gastric cancer (GC) and normal stomach tissues and to investigate the prognostic value of the upregulated gene KCND2. A retrospective analysis was performed using data from large available databases. KCND2 was significantly upregulated at the mRNA and protein levels in GC compared with that in normal stomach tissues. High KCND2 RNA expression was independently associated with shorter overall survival (HR: 1.634, 95% CI: 1.135-2.352; p=0.008) and recurrence-free survival (HR: 2.644, 95% CI: 1.438-4.863; p=0.002). Data mining in the Kaplan-Meier plotter confirmed the prognostic value of KCND2. KCND2 upregulation is a valuable prognostic biomarker in GC patients, in terms of overall survival and recurrence-free survival.

Voltage-Gated Calcium Influx Modifies Cholinergic Inhibition of Inner Hair Cells in the Immature Rat Cochlea.

Until postnatal day (P) 12, inner hair cells of the rat cochlea are invested with both afferent and efferent synaptic connections. With the onset of hearing at P12, the efferent synapses disappear, and afferent (ribbon) synapses operate with greater efficiency. This change coincides with increased expression of voltage-gated potassium channels, the loss of calcium-dependent electrogenesis, and the onset of graded receptor potentials driven by sound. The transient efferent synapses include near-membrane postsynaptic cisterns thought to regulate calcium influx through the hair cell's α9-containing and α10-containing nicotinic acetylcholine receptors. This influx activates small-conductance Ca2+-activated K+ (SK) channels. Serial-section electron microscopy of inner hair cells from two 9-d-old (male) rat pups revealed many postsynaptic efferent cisterns and presynaptic afferent ribbons whose average minimal separation in five cells ranged from 1.1 to 1.7 μm. Efferent synaptic function was studied in rat pups (age, 7-9 d) of either sex. The duration of these SK channel-mediated IPSCs was increased by enhanced calcium influx through L-type voltage-gated channels, combined with ryanodine-sensitive release from internal stores-presumably the near-membrane postsynaptic cistern. These data support the possibility that inner hair cell calcium electrogenesis modulates the efficacy of efferent inhibition during the maturation of inner hair cell synapses.SIGNIFICANCE STATEMENT Strict calcium buffering is essential for cellular function. This problem is especially acute for compact hair cells where increasing cytoplasmic calcium promotes the opposing functions of closely adjoining afferent and efferent synapses. The near-membrane postsynaptic cistern at efferent synapses segregates synaptic calcium signals by acting as a dynamic calcium store. The hair cell serves as an informative model for synapses with postsynaptic cisterns (C synapses) found in central neurons.

Role of Kv4.3 in Vibration-Induced Muscle Pain in the Rat.

We hypothesized that changes in the expression of voltage-gated potassium channel (Kv) 4.3 contribute to the mechanical hyperalgesia induced by vibration injury, in a rodent model for hand-arm vibration syndrome in humans. Here we show that the exposure of the gastrocnemius muscle to vibration injury induces muscle hyperalgesia that is accompanied by a significant downregulation of Kv4.3 in affected sensory nerve fibers in dorsal root ganglia. We additionally show that the intrathecal administration of antisense oligonucleotides for Kv4.3 messenger RNA itself induces muscle hyperalgesia in the rat. Our results suggest that attenuation in the expression of Kv4.3 may contribute to neuropathic pain in people affected by hand-arm vibration syndrome. Our findings establish Kv4.3 as a potential molecular target for the treatment of hand-arm vibration syndrome.

Down-regulation of A-type potassium channel in gastric-specific DRG neurons in a rat model of functional dyspepsia.

Although without evidence of organic structural abnormalities, pain or discomfort is a prominent symptom of functional dyspepsia and considered to reflect visceral hypersensitivity whose underlying mechanism is poorly understood. Here, we studied electrophysiological properties and expression of voltage-gated potassium channels in dorsal root ganglion (DRG) neurons in a rat model of functional dyspepsia induced by neonatal gastric irritation. Male Sprague-Dawley rat pups at 10-day old received 0.1% iodoacetamide (IA) or vehicle by oral gavage for 6 days and studied at adulthood. Retrograde tracer-labeled gastric-specific T8 -T12 DRG neurons were harvested for the patch-clamp study in voltage and current-clamp modes and protein expression of K(+) channel in T8 -T12 DRGs was examined by western blotting. (1) Gastric specific but not non-gastric DRG neurons showed an enhanced excitability in neonatal IA-treated rats compared to the control: depolarized resting membrane potentials, a lower current threshold for action potential (AP) activation, and an increase in the number of APs in response to current stimulation. (2) The current density of tetraethylammonium insensitive (transiently inactivating A-type current), but not the tetraethylammonium sensitive (slow-inactivating delayed rectifier K(+) currents), was significantly smaller in IA-treated rats (65.4 ± 6.9 pA/pF), compared to that of control (93.1 ± 8.3 pA/pF). (3) Protein expression of KV 4.3 was down-regulated in IA-treated rats. A-type potassium channels are significantly down-regulated in the gastric-specific DRG neurons in adult rats with mild neonatal gastric irritation, which in part contribute to the enhanced DRG neuron excitabilities that leads to the development of gastric hypersensitivity.

Potential therapeutic targets for hypoxia-induced pulmonary artery hypertension

BackgroundHypoxic pulmonary artery hypertension (PAH) as a severe pulmonary disease is characterized by changes of pulmonary vascular reconstruction. Mitochondrial ATP-sensitive potassium channel (mitoKATP) was considered as one of factors responsible for the proliferation of hypoxic pulmonary arterial smooth muscle cells (PASMCs), although the exact mechanisms remain unclear.MethodsPulmonary artery hypertension was induced in rats with or without 5-hydroxydecanoate (5-HD). The mean pulmonary artery pressure, morphologic changes, mRNA and protein expressions of voltage-gated potassium channels (Kv1.5 channel), were measured. The concentrations of monocyte chemo-attractant protein-1 (MCP-1) and transforming growth factor-beta1 (TGF-β1) were detected. Furthermore, pulmonary arterial smooth muscle cells (PASMCs) were isolated and cultured with or without hypoxia pretreated with or without 5-HD or/and Kv1.5 inhibitor 4-aminopyridine (4-AP). Mitochondrial membrane potential (Δψm) and the proliferation of PASMCs were detected.Results5-HD significantly prevented the development of PAH by blocking the mitochondrial membrane depolarization, increased the expression of voltage-gated potassium channels, and reduced pulmonary hypertension mediated by TGF-β1 or MCP-1 signaling pathway.ConclusionThe MitoKATP plays an important role in the development of PAH and may be therapeutic target for the treatment of disease.

Diet-induced obesity causes long QT and reduces transcription of voltage-gated potassium channels

In humans, obesity is associated with long QT, increased frequency of premature ventricular complexes, and sudden cardiac death. The mechanisms of the pro-arrhythmic electrophysiologic remodeling of obesity are poorly understood. We tested the hypothesis that there is decreased expression of voltage-gated potassium channels in the obese heart, leading to long QT. Using implanted telemeters, we found that diet-induced obese (DIO) wild-type mice have impaired cardiac repolarization, demonstrated by long QT, as well as more frequent ventricular ectopy, similar to obese humans. DIO mice have reduced protein and mRNA levels of the potassium channel Kv1.5 caused by a reduction of the transcription factor cyclic AMP response element binding protein (CREB) in DIO hearts. We found that CREB knock-down by siRNA reduces Kv1.5, CREB binds to the Kv1.5 promoter in the heart, and CREB increases transcription of mouse and human Kv1.5 promoters. The reduction in CREB protein during lipotoxicity can be rescued by inhibiting protein kinase D (PKD). Our results identify a mechanism for obesity-induced electrophysiologic remodeling in the heart, namely PKD-induced reduction of CREB, which in turn decreases expression of the potassium channel Kv1.5.

Neuroinflammation and oxidative stress in rostral ventrolateral medulla contribute to neurogenic hypertension induced by systemic inflammation

BackgroundIn addition to systemic inflammation, neuroinflammation in the brain, which enhances sympathetic drive, plays a significant role in cardiovascular diseases, including hypertension. Oxidative stress in rostral ventrolateral medulla (RVLM) that augments sympathetic outflow to blood vessels is involved in neural mechanism of hypertension. We investigated whether neuroinflammation and oxidative stress in RVLM contribute to hypertension following chronic systemic inflammation.MethodsIn normotensive Sprague-Dawley rats, systemic inflammation was induced by infusion of Escherichia coli lipopolysaccharide (LPS) into the peritoneal cavity via an osmotic minipump. Systemic arterial pressure and heart rate were measured under conscious conditions by the non-invasive tail-cuff method. The level of the inflammatory markers in plasma or RVLM was analyzed by ELISA. Protein expression was evaluated by Western blot or immunohistochemistry. Tissue level of superoxide anion (O2·-) in RVLM was determined using the oxidation-sensitive fluorescent probe dihydroethidium. Pharmacological agents were delivered either via infusion into the cisterna magna with an osmotic minipump or microinjection bilaterally into RVLM.ResultsIntraperitoneal infusion of LPS (1.2 mg/kg/day) for 14 days promoted sustained hypertension and induced a significant increase in plasma level of C-reactive protein, tumor necrosis factor-α (TNF-α), or interleukin-1β (IL-1β). This LPS-induced systemic inflammation was accompanied by activation of microglia, augmentation of IL-1β, IL-6, or TNF-α protein expression, and O2·- production in RVLM, all of which were blunted by intracisternal infusion of a cycloxygenase-2 (COX-2) inhibitor, NS398; an inhibitor of microglial activation, minocycline; or a cytokine synthesis inhibitor, pentoxifylline. Neuroinflammation in RVLM was also associated with a COX-2-dependent downregulation of endothelial nitric oxide synthase and an upregulation of intercellular adhesion molecule-1. Finally, the LPS-promoted long-term pressor response and the reduction in expression of voltage-gated potassium channel, Kv4.3 in RVLM were antagonized by minocycline, NS398, pentoxifylline, or a superoxide dismutase mimetic, tempol, either infused into cisterna magna or microinjected bilaterally into RVLM. The same treatments, on the other hand, were ineffective against LPS-induced systemic inflammation.ConclusionThese results suggest that systemic inflammation activates microglia in RVLM to induce COX-2-dependent neuroinflammation that leads to an increase in O2·- production. The resultant oxidative stress in RVLM in turn mediates neurogenic hypertension.

Butamben derivatives enhance BMP-2-stimulated commitment of C2C12 cells into osteoblasts with induction of voltage-gated potassium channel expression

As the primary step for 'drug repositioning', we evaluated the effect of 2000 drugs and drug candidates on the commitment of bi-potential mesenchymal precursor C2C12 cells into osteoblasts in the presence of bone morphogenetic protein (BMP)-2 and found that butamben enhanced BMP-2-stimulated induction of alkaline phosphatase, a biomarker of osteoblastogenesis. Investigating the underlying mechanism of its anabolic actions, we found anabolic action of its derivative (compound 4) relies on BMP-2 signaling and mRNA induction of BMPs and voltage-gated potassium channels.

Voltage-gated potassium channel in a human skin squamous cell carcinoma cell line A431

Objective To investigate the role of voltage-gated potassium channel in the human skin squamous cell carcinoma A431 cells and human keratinocyte HaCaT cells. Methods MTT assay was performed to detect the effect of different concentrations of tetraethylammonium (TEA) on the proliferation of cultured A431 cells and HaCaT cells. Besides, enzyme-linked immunosorbent assay (ELISA) was conducted to detect the expression of HERG channel protein in A431 cells, HaCaT cells and normal human skin tissue.Results TEA inhibited the proliferation of A431 cells and HaCaT cells in a dose- and time-dependent manner.After treated with TEA (≥ 10 mmol/L) for 24 or more hours, the proliferation of A431 cells and HaCaT cells was obviously suppressed. A significant difference was observed in the average concentration of HERG channel protein between A431 cells, HaCaT cells and normal human skin tissue (49.7114 ± 3.55696 pg/ml, 35.7471 ±4.14696 pg/ml, 36.8857 ± 3.47810 pg/ml, all P < 0.05). Conclusions The block of voltage-gated potassium channel could inhibit the proliferation of A431 cells and HaCaT cells, and the expression of voltage-gated potassium channel seems to be higher in human skin squamous cell carcinoma cells. Key words: Neoplasms, squamous cell; Potassium channels, voltage-gated; Keratinocytes

Selective underexpression of Kv3.2 and Kv3.4 channels in the cortex of rats exposed to ethanol during early postnatal life

The expression of voltage-gated potassium channels belonging to the Kv3 family has been studied in the sensori-motor cortex of rats exposed to alcohol inhalation during the first postnatal week (P2-P6). The study was carried out using comparative RT-PCR. At P9, a significant reduction of the expression of Kv3.2 and Kv3.4 subunits occurred in alcohol-treated animals, as compared with controls. The expression of the Kv3.4a splicing variant, which is thought to be critically involved in the high-frequency firing of some cortical interneurons, was also correspondingly reduced. The downregulation of Kv3.2 and Kv3.4a subunits represented a long-lasting effect of alcohol exposure, since it was also observed in P24 animals. The expression of both Kv3.1 and Kv3.3 channels appeared to be not significantly affected by alcohol exposure. An increased susceptibility to apoptotic neuronal death after early postnatal exposure to ethanol was confirmed by the lower bcl-2/bax ratio observed in alcohol-treated animals. Although Kv3.4 subunits are thought to trigger apoptosis, the lack of upregulation in our model argues against their involvement in the mechanism leading to alcohol-induced apoptosis. The possible consequences of the selective downregulation of Kv3 subunits on the cortical function, as well as their relevance for the genesis of fetal alcohol effects, are discussed.

Hypoxia-induced 15-HETE enhances the constriction of internal carotid arteries by down-regulating potassium channels

Severe hypoxia induces the constriction of internal carotid arteries (ICA), which worsens ischemic stroke in the brain. A few metabolites are presumably involved in hypoxic vasoconstriction, however, less is known about how such molecules provoke this vasoconstriction. We have investigated the influence of 15-hydroxyeicosatetrienoic acid (15-HETE) produced by 15-lipoxygenase (15-LOX) on vasoconstriction during hypoxia. As showed in our results, 15-LOX level increases in ICA endothelia and smooth muscles. 15-HETE enhances the tension of ICA ring in a dose-dependent manner, as well as attenuates the activities and expression of voltage-gated potassium channels (Kv 1.5 and Kv 2.1). Therefore, the down-regulation of Kv channels by 15-HETE during hypoxia may weaken the repolarization of action potentials and causes a dominant influx of calcium ions to enhance smooth muscle tension and ICA constriction.

Abstract 2623: Right Ventricular Hypertrophy in Monocrotaline-induced Pulmonary Hypertension is Associated with Impaired Oxidative Metabolism and Action Potential Prolongation

Introduction: Right ventricular hypertrophy (RVH) and right ventricular failure are major determinants of prognosis and functional state in pulmonary artery hypertension (PAH). We previously found a mitochondrial metabolic shift in the pulmonary circulation in clinical as well as experimental PAH that includes a shift from oxidation to glycolysis, decreased production of reactive oxygen species (ROS) and normoxic activation of HIF-1α and decreased expression of voltage-gated potassium channels. In this study, we hypothesize that during RVH there is a similar metabolic shift in the RV characterized by impaired mitochondrial respiration and that the resulting electrical remodeling causes action potential prolongation. Methods and Results: PAH was induced in Sprague-Dawley rats by single injection of monocrotaline (60mg/Kg). At 3 weeks, PAH was confirmed by a shortened pulmonary artery acceleration time vs controls (13.8±0.7 vs 36.2±0.2 msec, P &lt; 0.001) as determined by Doppler Echo. RVH was also evident, with a thicker right ventricular free wall in monocrotaline vs control hearts (1.3±0.1 vs 0.9±0.0 mm, P &lt; 0.001 vs control) as assessed by two-dimensional and M-mode Echo. Oxygen consumption of right ventricular tissues (140mg samples) was measured using high-resolution respirometry. In an RV Langendorff model, RV systolic pressure (RVSP) and RV monophasic action potential duration (MAP) were measured. The ratio of RV/LV+S weight increased to 2 fold with monocrotaline (P &lt; 0.001). RVSP in MCT group was increased to 50.9±10.6 vs 21.3±2.7 mmHg, P &lt; 0.05). RV O2-consumption in RVH was significantly reduced vs control [144.1±37.6 vs 277.0±27.4 pmol/(sec*ml), P &lt; 0.05]. The duration of 90% and 75% repolarization of MAP (MAPD90 and MAPD75) was markedly prolonged in RVH (145% and 136% vs controls; P &lt; 0.001, P &lt; 0.05, respectively). Importantly, MAPD90 increased in direct proportion to the severity of PAH, as measured by RVSP. Conclusions: RVH was associated with impaired RV metabolism as evidenced by reduced O2 consumption. This metabolic shift was associated with significant action potential prolongation in the RV. The consequences of this ionic remodeling for arrhythmogenisis and contractility remain to be determined.

Identification of an Evolutionarily Conserved Extracellular Threonine Residue Critical for Surface Expression and Its Potential Coupling of Adjacent Voltage-sensing and Gating Domains in Voltage-gated Potassium Channels

The dynamic expression of voltage-gated potassium channels (Kvs) at the cell surface is a fundamental factor controlling membrane excitability. In exploring possible mechanisms controlling Kv surface expression, we identified a region in the extracellular linker between the first and second of the six (S1-S6) transmembrane-spanning domains of the Kv1.4 channel, which we hypothesized to be critical for its biogenesis. Using immunofluorescence microscopy, flow cytometry, patch clamp electrophysiology, and mutagenesis, we identified a single threonine residue at position 330 within the Kv1.4 S1-S2 linker that is absolutely required for cell surface expression. Mutation of Thr-330 to an alanine, aspartate, or lysine prevented surface expression. However, surface expression occurred upon co-expression of mutant and wild type Kv1.4 subunits or mutation of Thr-330 to a serine. Mutation of the corresponding residue (Thr-211) in Kv3.1 to alanine also caused intracellular retention, suggesting that the conserved threonine plays a generalized role in surface expression. In support of this idea, sequence comparisons showed conservation of the critical threonine in all Kv families and in organisms across the evolutionary spectrum. Based upon the Kv1.2 crystal structure, further mutagenesis, and the partial restoration of surface expression in an electrostatic T330K bridging mutant, we suggest that Thr-330 hydrogen bonds to equally conserved outer pore residues, which may include a glutamate at position 502 that is also critical for surface expression. We propose that Thr-330 serves to interlock the voltage-sensing and gating domains of adjacent monomers, thereby yielding a structure competent for the surface expression of functional tetramers.

Altered expression of voltage-gated potassium channel 4.2 and voltage-gated potassium channel 4-interacting protein, and changes in intracellular calcium levels following lithium-pilocarpine-induced status epilepticus

The A-type voltage-gated potassium channels (Kv4) have been proved to play a major role as modulators of somatodendritic excitability. Recent studies indicate that neuronal hyperactivity in epilepsy is associated with changes in Kv4. However, the precise regulation of Kv4 in the development of epilepsy and its underlying mechanism remain unclear. In this study, we investigated whether the expression of the Kv4.2 channel and of its major modulator, voltage-dependent potassium channel-interacting protein (KChIP1), is altered following lithium-pilocarpine induced status epilepticus (SE) and the chronic-epilepsy phase in the rat model. We found that Kv4.2 and KChIP1 expression was transiently up-regulated following SE, whereas it was down-regulated during the chronic phase: this was most prominent in the CA1 and CA3 regions. The time-course analysis of the protein expression level showed that the peak Kv4.2 up-regulation was between 6 and 24 h after SE, whereas KChIP1 expression was increased earlier and for a shorter period. The temporospatial changes in Kv4.2 were very similar to those of its major modulator KChIP1. We compared the difference in 4-aminopyridine (4-AP)-induced intracellular calcium ([Ca2+]i) elevation between model and control brain slices. The results showed that the [Ca2+]i elevation induced by the Kv4 channel blocker 4-AP was aggravated and prolonged in the model slice after SE. The functional relevance of these changes in Ca2+ homeostasis and Kv4.2 and KChIP1 expression may be associated with intrinsic neuronal excitability regulation and epileptogenesis.

Expression of Voltage-Gated Potassium Channels in Human and Mouse Colonic Carcinoma

Voltage-gated Kv potassium channels, like ether a go-go (EAG) channels, have been recognized for their oncogenic potential in breast cancer and other malignant tumors. We examined the molecular and functional expression of Kv channels in human colonic cancers and colon of mice treated with the chemical carcinogens dimethylhydrazine and N-methyl-N-nitrosourea. The data were compared with results from control mice and animals with chemically induced DSS colitis. Electrogenic salt transport by amiloride-sensitive Na+ channels and cyclic AMP-activated cystic fibrosis transmembrane conductance regulator Cl- channels were attenuated during tumor development and colitis, whereas Ca2+-dependent transport remained unchanged. Kv channels, in particular Eag-1, were enhanced during carcinogenesis. Multiplex reverse transcription-PCR showed increased mRNA expression for Kv1.3, Kv1.5, Kv3.1, and members of the Eag channel family, after dimethylhydrazine and N-methyl-N-nitrosourea treatment. Eag-1 protein was detected in the malignant mouse colon and human colonic cancers. Genomic amplification of Eag-1 was found in 3.4% of all human colorectal adenocarcinoma and was an independent marker of adverse prognosis. The study predicts an oncogenic role of Kv and Eag channels for the development of colonic cancer. These channels may represent an important target for a novel pharmacotherapy of colonic cancer.

Developmental changes in the expression of voltage-gated potassium channels in the ductus arteriosus of the fetal rat

Oxygen-sensitive, voltage-gated potassium channels (Kv) may contribute to the determination of the membrane potential in smooth muscle cells of the ductus arteriosus (DA), and thus to regulation of contractile tone in response to oxygen. Developmental changes in Kv during gestation may be related to closure of the DA after birth. This study investigated developmental changes in the expression of Kv in the DA and compared it with that of the pulmonary artery (PA) and the aorta (Ao). The DA, PA, and Ao were isolated from fetal rats at days 19 and 21 of gestation (term: 21.5 days). The expression of Kv1.2, Kv1.5, Kv2.1, and Kv3.1, putative oxygen-sensitive Kv channels that open in response to oxygen, was evaluated at both the mRNA and protein levels, using quantitative real-time polymerase chain reaction and immunohistochemistry. In the Kv family studied, Kv1.5 mRNA was expressed most abundantly in the DA, PA, and Ao in both day-19 and day-21 fetuses. Although the expression levels of Kv1.2, Kv1.5, Kv2.1, and Kv3.1 did not change much with development in the PA and Ao, in the DA they decreased with development. The decrease in the expression of Kv channels may enhance DA closure after birth by eliminating the opening of Kv channels when oxygen increases.

Messenger RNA and protein expression analysis of voltage-gated potassium channels in the brain of Abeta(25-35)-treated rats.

Potassium channel dysfunction has been implicated in Alzheimer's disease. In the present study, the expression of voltage-gated potassium channel (Kv) subunits in rat brain was measured after a single intracerebroventricular injection of beta-amyloid peptide 25-35 (Abeta(25-35)). After injection of Abeta, the spatial memory of rats was significantly impaired in the Morris water maze. Expression of five main Kv channel subunits (Kv1.5, Kv2.1, Kv1.4, Kv4.2, and Kv4.3) in mRNA level was assessed by using reverse transcription-polymerase chain reaction (RT-PCR). The mRNA levels of Kv2.1 and Kv1.4 were increased by 72% and 67%, respectively, in hippocampus, and Kv4.2 mRNA was increased by 58% in cortex. No other significant mRNA expression changes were found in Abeta-treated rats. The protein expression of Kv2.1, Kv1.4, and Kv4.2 was detected by using Western blotting. Kv2.1 and Kv1.4 protein levels were increased by 48% and 50%, respectively, in hippocampus of Abeta-treated rats, and Kv4.2 protein was increased by 42% in cerebral cortex. This study indicates that the expression up-regulation of Kv1.4, Kv2.1, and Kv4.2 in Abeta-induced cognitive impairment might play an important role in the pathogenesis of Alzheimer's disease.