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1.
Potassium channels and their role in glioma: A mini review.
Liu, J, Qu, C, Han, C, Chen, MM, An, LJ, Zou, W
Molecular membrane biology. 2019;(1):76-85
Abstract
K+ channels regulate a multitude of biological processes and play important roles in a variety of diseases by controlling potassium flow across cell membranes. They are widely expressed in the central and peripheral nervous system. As a malignant tumor derived from nerve epithelium, glioma has the characteristics of high incidence, high recurrence rate, high mortality rate, and low cure rate. Since glioma cells show invasive growth, current surgical methods cannot completely remove tumors. Adjuvant chemotherapy is still needed after surgery. Because the blood-brain barrier and other factors lead to a lower effective concentration of chemotherapeutic drugs in the tumor, the recurrence rate of residual lesions is extremely high. Therefore, new therapeutic methods are needed. Numerous studies have shown that different K+ channel subtypes are differentially expressed in glioma cells and are involved in the regulation of the cell cycle of glioma cells to arrest them at different stages of the cell cycle. Increasing evidence suggests that K+ channels express in glioma cells and regulate glioma cell behaviors such as cell cycle, proliferation and apoptosis. This review article aims to summarize the current knowledge on the function of K+ channels in glioma, suggests K+ channels participating in the development of glioma.
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Photolithographic Fabrication of Micro Apertures in Dry Film Polymer Sheets for Channel Recordings in Planar Lipid Bilayers.
Khoury, ME, Winterstein, T, Weber, W, Stein, V, Schlaak, HF, Thiel, G
The Journal of membrane biology. 2019;(2-3):173-182
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Abstract
Planar lipid bilayers constitute a versatile method for measuring the activity of protein channels and pores on a single molecule level. Ongoing efforts attempt to tailor this method for detecting biomedically relevant target analytes or for high-throughput screening of drugs. To improve the mechanical stability of bilayer recordings, we use a thin-film epoxy resist ADEX as septum in free-standing vertical bilayers. Defined apertures with diameters between 30 µm and 100 µm were micro-fabricated by photolithography. The performance of these septa was tested by functional reconstitution of the K+ channel KcvNTS in lipid bilayers spanned over apertures in ADEX or Teflon films; the latter is conventionally used in bilayer recordings and serves as reference. We observe that the functional properties of the K+ channel are identical in both materials while ADEX provides no advantage in terms of capacitance and signal-to-noise ratio. In contrast to Teflon, however, ADEX enables long-term experimental recordings while the stability of the lipid bilayer is not compromised by pipetting solutions in and out of the recording chamber. Combined with the fact that the ADEX films can be cleaned with acetone, our results suggest that ADEX carries great potential for multiplexing bilayer chambers in robust and reusable sensing devices.
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Genetics and postsurgical neuropathic pain: An ancillary study of a multicentre survey.
Blanc, P, Génin, E, Jesson, B, Dubray, C, Dualé, C, ,
European journal of anaesthesiology. 2019;(5):342-350
Abstract
BACKGROUND Neuropathic pain following surgery could be a useful model for the study of the genetic mechanisms of peripheral neuropathic pain. OBJECTIVE The aim of this study was to identify genetic predictors of persistent postsurgical neuropathic pain. DESIGN An ancillary study from a prospective cohort. SETTING Eighteen French university hospitals. PATIENTS Five hundred and sixty-one patients at risk of persistent postoperative pain who underwent scheduled surgery were classified as 159 cases and 402 controls. INTERVENTION Pre-operative blood sampling for DNA analysis and questionnaires sent at the third and sixth month after surgery. MAIN OUTCOME MEASURES The phenotype was the report of pain at the site of surgery with a positive response in the DN4 questionnaire within 6 months after surgery. Out of a list of 126 candidate genes involved in the initial processes of peripheral neuropathic pain, a set of 4599 single nucleotide polymorphisms was tested on an Illumina chip. We carried out the association tests, based on an additive model, on 4422 single nucleotide polymorphisms. RESULTS After correcting for type-I error inflation, only one suggestive association was reached for one single nucleotide polymorphism, the rs2286614, which we had selected to tag KCNK4. This gene encodes for TRAAK, a two-pore domain background K channel involved in the modulation of the primary thermoreceptors of the transient receptor potential channels family. CONCLUSION This is the first genetic association study specifically investigating the occurrence of persistent postsurgical neuropathic pain. Its results help target future research to better understand the mechanisms of peripheral neuropathic pain. TRIAL REGISTRATION ClinicalTrials.gov (ref. NCT00812734).
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Selectivity of the KcsA potassium channel: Analysis and computation.
Song, Z, Cao, X, Horng, TL, Huang, H
Physical review. E. 2019;(2-1):022406
Abstract
Ion channels regulate the flux of ions through cell membranes and play significant roles in many physiological functions. Most of the existing literature focuses on computational approaches based on molecular dynamics simulation or numerical solution of the modified Poisson-Nernst-Planck (PNP) system. In this paper, we present an analytical and computational study of a mathematical model of the KcsA potassium channel, including the effects of ion size (Bikerman model) and solvation energy (Born model). Under equilibrium conditions, we obtain an analytical solution of our modified PNP system, which is used to explain selectivity of KcsA of various ions (K^{+}, Na^{+}, Cl^{-}, Ca^{2+}, and Ba^{2+}) due to negative permanent charges inside the filter region and the effect of ion sizes. Our results show that K^{+} is always selected over Na^{+}, as smaller Na^{+} ions have larger solvation energy. As the amount of negative charges in the filter exceeds a critical value, divalent ions (Ca^{2+} and Ba^{2+}) can enter the filter region and block the KcsA channel. For the nonequilibrium cases, due to difficulties associated with a pure analytical or numerical approach, we use a hybrid analytical-numerical method to solve the modified PNP system. Our predictions of selectivity of KcsA channels and saturation phenomenon of the current-voltage (I-V) curve agree with experimental observations.
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TEA-sensitive K+ channels and human eccrine sweat gland output.
Mack, GW, Smith, BS, Rowland, B
Journal of applied physiology (Bethesda, Md. : 1985). 2019;(4):921-929
Abstract
Cholinergic-activated sweating depends on an influx of Ca2+ from extracellular fluid. It is thought that the opening of K+ channels on secretory epithelial cells facilitates Ca2+ entry. We examined the hypothesis that tetraethylammonium (TEA)-sensitive K+ channels participate in sweat production. We used a pre-post experimental design and initiated cholinergic-mediated sweating with intradermal electrical stimulation, monitored local sweat rate (SR) with a small sweat capsule mounted on the skin, and delivered 50 mM TEA via intradermal microdialysis. Local SR was activated by intradermal stimulation frequencies of 0.2-64 Hz, and we generated a sigmoid-shaped stimulus-response curve by plotting the area under the SR-time curve versus log10 stimulus frequency. Peak local SR was reduced from 0.372 ± 0.331 to 0.226 ± 0.190 mg·min-1·cm-2 (P = 0.0001) during application of 50 mM TEA, whereas the EC50 and Hill slopes were not altered. The global sigmoid-shaped stimulus-response curves for control and 50 mM TEA were significantly different (P < 0.0001), and the plateau region was significantly reduced (P = 0.0023) with the TEA treatment. The effect of TEA on peak local SR was similar in male and female subjects. However, we did note a small effect of sex on the shape of the stimulus-response curves during intradermal electrical stimulation. Overall, these data support the hypothesis that cholinergic control of sweat gland activity is modulated by the presence of TEA-sensitive K+ channels in human sweat gland epithelial cells.NEW & NOTEWORTHY The contribution of various potassium channels to the process of cholinergic-mediated human eccrine sweat production is unclear. Using a novel model for cholinergic-mediated sweating in humans, we provide evidence that tetraethylammonium-sensitive K+ channels (KCa1.1 and Kv channels) contribute to eccrine sweat production.
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Contribution of potassium channels to action potential repolarization of human embryonic stem cell-derived cardiomyocytes.
Wang, Y, Zhu, R, Tung, L
British journal of pharmacology. 2019;(15):2780-2794
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Abstract
BACKGROUND AND PURPOSE The electrophysiological properties of human pluripotent stem cell-derived cardiomyocytes (CMs) have not yet been characterized in a syncytial context. This study systematically characterized the contributions of different repolarizing potassium currents in human embryonic stem cell-derived CMs (hESC-CMs) during long-term culture as cell monolayers. EXPERIMENTAL APPROACH The H9 hESC line was differentiated to CMs and plated to form confluent cell monolayers. Optical mapping was used to record the action potentials (APs) and conduction velocity (CV) during electrophysiological and pharmacological experiments. RT-PCR and Western blot were used to detect the presence and expression levels of ion channel subunits. KEY RESULTS Long-term culture of hESC-CMs led to shortened AP duration (APD), faster repolarization rate, and increased CV. Selective block of IKr , IKs , IK1 , and IKur significantly affected AP repolarization and APD in a concentration- and culture time-dependent manner. Baseline variations in APD led to either positive or negative APD dependence of drug response. Chromanol 293B produced greater relative AP prolongation in mid- and late-stage cultures, while DPO-1 had more effect in early-stage cultures. CV in cell monolayers in early- and late-stage cultures was most susceptible to slowing by E-4031 and BaCl2 respectively. CONCLUSIONS AND IMPLICATIONS IKr , IKs , IK1 , and IKur all play an essential role in the regulation of APD and CV in hESC-CMs. During time in culture, increased expression of IKr and IK1 helps to accelerate repolarization, shorten APD, and increase CV. We identified a new pro-arrhythmic parameter, positive APD dependence of ion channel block, which can increase APD and repolarization gradients.
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Naringenin as an opener of mitochondrial potassium channels in dermal fibroblasts.
Kampa, RP, Kicinska, A, Jarmuszkiewicz, W, Pasikowska-Piwko, M, Dolegowska, B, Debowska, R, Szewczyk, A, Bednarczyk, P
Experimental dermatology. 2019;(5):543-550
Abstract
Flavonoids belong to a large group of polyphenolic compounds that are widely present in plants. Certain flavonoids, including naringenin, have cytoprotective properties. Although the antioxidant effect has long been thought to be a crucial factor accounting for the cellular effects of flavonoids, mitochondrial channels have emerged recently as targets for cytoprotective strategies. In the present study, we characterized interactions between naringenin and the mitochondrial potassium (mitoBKCa and mitoKATP ) channels recently described in dermal fibroblasts. With the use of the patch-clamp technique and mitoplasts isolated from primary human dermal fibroblast cells, our study shows that naringenin in micromolar concentrations leads to an increase in mitoBKCa channel activity. The opening probability of the channel decreased from 0.97 in the control conditions (200 μmol/L Ca2+ ) to 0.06 at a low Ca2+ level (1 μmol/L) and increased to 0.85 after the application of 10 μmol/L naringenin. Additionally, the activity of the mitoKATP channel increased following the application of 10 μmol/L naringenin. To investigate the effects of naringenin on mitochondrial function, the oxygen consumption of dermal fibroblast cells was measured in potassium-containing media. The addition of naringenin significantly and dose-dependently increased the respiratory rate from 5.8 ± 0.2 to 14.0 ± 0.6 nmol O2 × min-1 × mg protein-1 . Additionally, a Raman spectroscopy analysis of skin penetration indicated that the naringenin was distributed in all skin layers, including the epidermis and dermis. In this study, we demonstrated that a flavonoid, naringenin, can activate two potassium channels present in the inner mitochondrial membrane of dermal fibroblasts.
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Mutations in KCNK4 that Affect Gating Cause a Recognizable Neurodevelopmental Syndrome.
Bauer, CK, Calligari, P, Radio, FC, Caputo, V, Dentici, ML, Falah, N, High, F, Pantaleoni, F, Barresi, S, Ciolfi, A, et al
American journal of human genetics. 2018;(4):621-630
Abstract
Aberrant activation or inhibition of potassium (K+) currents across the plasma membrane of cells has been causally linked to altered neurotransmission, cardiac arrhythmias, endocrine dysfunction, and (more rarely) perturbed developmental processes. The K+ channel subfamily K member 4 (KCNK4), also known as TRAAK (TWIK-related arachidonic acid-stimulated K+ channel), belongs to the mechano-gated ion channels of the TRAAK/TREK subfamily of two-pore-domain (K2P) K+ channels. While K2P channels are well known to contribute to the resting membrane potential and cellular excitability, their involvement in pathophysiological processes remains largely uncharacterized. We report that de novo missense mutations in KCNK4 cause a recognizable syndrome with a distinctive facial gestalt, for which we propose the acronym FHEIG (facial dysmorphism, hypertrichosis, epilepsy, intellectual disability/developmental delay, and gingival overgrowth). Patch-clamp analyses documented a significant gain of function of the identified KCNK4 channel mutants basally and impaired sensitivity to mechanical stimulation and arachidonic acid. Co-expression experiments indicated a dominant behavior of the disease-causing mutations. Molecular dynamics simulations consistently indicated that mutations favor sealing of the lateral intramembrane fenestration that has been proposed to negatively control K+ flow by allowing lipid access to the central cavity of the channel. Overall, our findings illustrate the pleiotropic effect of dysregulated KCNK4 function and provide support to the hypothesis of a gating mechanism based on the lateral fenestrations of K2P channels.
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Beneficial Effects of High Potassium: Contribution of Renal Basolateral K+ Channels.
Staruschenko, A
Hypertension (Dallas, Tex. : 1979). 2018;(6):1015-1022
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Precision therapy for epilepsy due to KCNT1 mutations: A randomized trial of oral quinidine.
Mullen, SA, Carney, PW, Roten, A, Ching, M, Lightfoot, PA, Churilov, L, Nair, U, Li, M, Berkovic, SF, Petrou, S, et al
Neurology. 2018;(1):e67-e72
Abstract
OBJECTIVE To evaluate quinidine as a precision therapy for severe epilepsy due to gain of function mutations in the potassium channel gene KCNT1. METHODS A single-center, inpatient, order-randomized, blinded, placebo-controlled, crossover trial of oral quinidine included 6 patients with severe autosomal dominant nocturnal frontal lobe epilepsy (ADNFLE) due to KCNT1 mutation. Order was block randomized and blinded. Four-day treatment blocks were used with a 2-day washout between. Dose started at 900 mg over 3 divided doses then, in subsequent participants, was reduced to 600 mg, then 300 mg. Primary outcome was seizure frequency measured on continuous video-EEG in those completing the trial. RESULTS Prolonged QT interval occurred in the first 2 patients at doses of 900 and 600 mg quinidine per day, respectively, despite serum quinidine levels well below the therapeutic range (0.61 and 0.51 μg/mL, reference range 1.3-5.0 μg/mL). Four patients completed treatment with 300 mg/d without adverse events. Patients completing the trial had very frequent seizures (mean 14 per day, SD 7, median 13, interquartile range 10-18). Seizures per day were nonsignificantly increased by quinidine (median 2, 95% confidence interval -1.5 to +5, p = 0.15) and no patient had a 50% seizure reduction. CONCLUSION Quinidine did not show efficacy in adults and teenagers with ADNFLE. Dose-limiting cardiac side effects were observed even in the presence of low measured serum quinidine levels. Although small, this trial suggests use of quinidine in ADNFLE is likely to be ineffective coupled with considerable cardiac risks. CLINICAL TRIALS REGISTRATION Australian Therapeutic Goods Administration Clinical Trial Registry (trial number 2015/0151). CLASSIFICATION OF EVIDENCE This study provides Class II evidence that for persons with severe epilepsy due to gain of function mutations in the potassium channel gene KCNT1, quinidine does not significantly reduce seizure frequency.