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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.
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4.
Effect of Ascertainment Bias on Estimates of Patient Mortality in Inherited Cardiac Diseases.
Nannenberg, EA, van Rijsingen, IAW, van der Zwaag, PA, van den Berg, MP, van Tintelen, JP, Tanck, MWT, Ackerman, MJ, Wilde, AAM, Christiaans, I
Circulation. Genomic and precision medicine. 2018;(10):e001797
Abstract
BACKGROUND Accurate estimates of survival are indispensable for cardiologists, clinical geneticists, and genetic counselors dealing with families with an inherited cardiac disease. However, a bias towards a more severe disease with a worse outcome in the first publications may not accurately represent the actual survival forecast. We, therefore, evaluated the effect of ascertainment bias on survival in 3 different inherited cardiac diseases (idiopathic ventricular fibrillation, SCN5A overlap syndrome, and arrhythmogenic cardiomyopathy) caused by a founder mutation. METHODS We collected mortality data from mutation-positive subjects with either DPP6-associated idiopathic ventricular fibrillation, SCN5A overlap syndrome, and PLN-R14del-mediated arrhythmogenic cardiomyopathy >2 to 10 years of ongoing clinical/cascade genetic screening. RESULTS The median age of survival in DPP6 mutation-positive subjects increased from 44.6 years in the original cohort from 2008 (n=60; 95% CI, 36.8-52.4 years) to 68.2 years in the extended cohort from 2012 (n=235; 95% CI, 64.6-71.7 years; P<0.001). In the SCN5A overlap syndrome, survival increased from 56.1 years in 1999 (n=86; 95% CI, 48.0-64.2 years) to 69.7 years in 2009 (n=197; 95% CI, 61.3-78.2 years; P=0.049). In PLN-R14del positive patients, the median age of survival increased from 63.5 years in 2010 (n=89; 95% CI, 59.1-68.0 years) to 65.2 years in 2012 (n=370; 95% CI, 62.0-68.3 years; P=0.046). CONCLUSIONS The median age of survival in 3 different inherited cardiac diseases with an established pathogenic substrate significantly increased once genetic testing and cascade screening extended, after the first publication that elucidated the discovery of the disease-susceptibility gene/mutation. This underscores the direct and negative influence of ascertainment bias on survival forecasts and the importance of ongoing clinical/genetic follow-up to establish the most accurate disease prognosis for genetically mediated heart diseases.
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5.
CW-EPR Spectroscopy and Site-Directed Spin Labeling to Study the Structural Dynamics of Ion Channels.
Tilegenova, C, Elberson, BW, Marien Cortes, D, Cuello, LG
Methods in molecular biology (Clifton, N.J.). 2018;:279-288
Abstract
Continuous-wave electron paramagnetic resonance spectroscopy (CW-EPR) and site-directed spin labeling (SDSL) are proven experimental approaches to assess the structural dynamics of proteins in general (Hubbell et al., Curr Opin Struct Biol 8(5):649-656, 1998; Kazmier et al., Curr Opin Struct Biol 45:100-108, 2016; Perozo et al., Science 285(5424):73-78, 1999). These techniques have been particularly effective assessing the structure of integral membrane proteins embedded in a lipid bilayer (Cortes et al., J Gen Physiol 117(2):165-180, 2001; Cuello et al., Science 306(5695):491-495, 2004; Dalmas et al., Structure 18(7):868-878, 2010; Li et al., Proc Natl Acad Sci U S A 112(44):E5926-5935, 2015; Perozo et al., J Gen Physiol 118(2):193-206, 2001), as well as determining the conformational changes associated with their biological function (Kazmier et al., Curr Opin Struct Biol 45:100-108, 2016; Perozo et al., Science 285(5424):73-78, 1999; Arrigoni et al., Cell 164(5):922-936, 2016; Dalmas et al., Nat Commun 5:3590, 2014; Dong et al., Science 308(5724):1023-1028, 2005; Farrens et al., Science 274(5288):768-770, 1996; Perozo et al., Nat Struct Biol 5(6):459-469, 1998; Perozo et al., Nature 418(6901):942-948, 2002). In this chapter, we described a practical guide for the spin-labeling, liposome reconstitution, and CW-EPR measurements of the prototypical bacterial K+ channel, KcsA.
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Letter by Vermeer et al Regarding Article, "Phenotypic Spectrum of HCN4 Mutations: A Clinical Case".
Vermeer, AMC, Christiaans, I, Lodder, EM
Circulation. Genomic and precision medicine. 2018;(5):e002160
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7.
Identification of Intrahelical Bifurcated H-Bonds as a New Type of Gate in K+ Channels.
Rauh, O, Urban, M, Henkes, LM, Winterstein, T, Greiner, T, Van Etten, JL, Moroni, A, Kast, SM, Thiel, G, Schroeder, I
Journal of the American Chemical Society. 2017;(22):7494-7503
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Abstract
Gating of ion channels is based on structural transitions between open and closed states. To uncover the chemical basis of individual gates, we performed a comparative experimental and computational analysis between two K+ channels, KcvS and KcvNTS. These small viral encoded K+ channel proteins, with a monomer size of only 82 amino acids, resemble the pore module of all complex K+ channels in terms of structure and function. Even though both proteins share about 90% amino acid sequence identity, they exhibit different open probabilities with ca. 90% in KcvNTS and 40% in KcvS. Single channel analysis, mutational studies and molecular dynamics simulations show that the difference in open probability is caused by one long closed state in KcvS. This state is structurally created in the tetrameric channel by a transient, Ser mediated, intrahelical hydrogen bond. The resulting kink in the inner transmembrane domain swings the aromatic rings from downstream Phes in the cavity of the channel, which blocks ion flux. The frequent occurrence of Ser or Thr based helical kinks in membrane proteins suggests that a similar mechanism could also occur in the gating of other ion channels.
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Rate-Dependent Role of IKur in Human Atrial Repolarization and Atrial Fibrillation Maintenance.
Aguilar, M, Feng, J, Vigmond, E, Comtois, P, Nattel, S
Biophysical journal. 2017;(9):1997-2010
Abstract
The atrial-specific ultrarapid delayed rectifier K+ current (IKur) inactivates slowly but completely at depolarized voltages. The consequences for IKur rate-dependence have not been analyzed in detail and currently available mathematical action-potential (AP) models do not take into account experimentally observed IKur inactivation dynamics. Here, we developed an updated formulation of IKur inactivation that accurately reproduces time-, voltage-, and frequency-dependent inactivation. We then modified the human atrial cardiomyocyte Courtemanche AP model to incorporate realistic IKur inactivation properties. Despite markedly different inactivation dynamics, there was no difference in AP parameters across a wide range of stimulation frequencies between the original and updated models. Using the updated model, we showed that, under physiological stimulation conditions, IKur does not inactivate significantly even at high atrial rates because the transmembrane potential spends little time at voltages associated with inactivation. Thus, channel dynamics are determined principally by activation kinetics. IKur magnitude decreases at higher rates because of AP changes that reduce IKur activation. Nevertheless, the relative contribution of IKur to AP repolarization increases at higher frequencies because of reduced activation of the rapid delayed-rectifier current IKr. Consequently, IKur block produces dose-dependent termination of simulated atrial fibrillation (AF) in the absence of AF-induced electrical remodeling. The inclusion of AF-related ionic remodeling stabilizes simulated AF and greatly reduces the predicted antiarrhythmic efficacy of IKur block. Our results explain a range of experimental observations, including recently reported positive rate-dependent IKur-blocking effects on human atrial APs, and provide insights relevant to the potential value of IKur as an antiarrhythmic target for the treatment of AF.
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Altered expression of ATP-sensitive K(+) channels in Hirschsprung's disease.
Tomuschat, C, O'Donnell, AM, Coyle, D, Dreher, N, Kelly, D, Puri, P
Journal of pediatric surgery. 2016;(6):948-52
Abstract
PURPOSE Hirschsprung's disease-associated enterocolitis (HAEC) is the most common cause of morbidity and mortality in Hirschsprung's disease (HSCR). Altered intestinal epithelial barrier function has been suggested to play a role in the causation of HAEC. In rodent experimental models of colitis, a decreased expression of K(ATP) channels (Subunits: Kir6.1/6.2 and SUR1/2) is reported. We designed this study to determine if K(ATP) channels exist within the human colon and to investigate the expression of different subunits in Hirschsprung's disease. METHODS We investigated Kir6.1, Kir6.2, SUR1, and SUR2 expression in ganglionic and aganglionic bowel of HD patients (n=5) and controls (n=5). Western blotting and confocal immunofluorescence were performed. MAIN RESULTS Western blot analysis revealed that Kir6.1, Kir6.2, SUR1, and SUR2 are strongly expressed in the normal human colon. Kir6.1, Kir6.2, SUR1, and SUR2 expression was significantly decreased in the aganglionic bowel compared to ganglionic bowel and controls. Kir6.1 and SUR1 expression were also significantly decreased in the ganglionic bowel of HSCR patients compared to controls. CONCLUSION We demonstrate for the first time the existence of K(ATP) channels in the human colon. The decreased K(ATP) channel expression in HSCR specimens suggests that an altered K(ATP) expression may interfere with intestinal epithelium barrier function and predispose to HAEC.
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Glucagon-like peptide-1 derived cardioprotection does not utilize a KATP-channel dependent pathway: mechanistic insights from human supply and demand ischemia studies.
Giblett, JP, Axell, RG, White, PA, Clarke, SJ, McCormick, L, Read, PA, Reinhold, J, Brown, AJ, O'Sullivan, M, West, NE, et al
Cardiovascular diabetology. 2016;:99
Abstract
BACKGROUND Glucagon-like peptide-1 (7-36) amide (GLP-1) protects against stunning and cumulative left ventricular dysfunction in humans. The mechanism remains uncertain but GLP-1 may act by opening mitochondrial K-ATP channels in a similar fashion to ischemic conditioning. We investigated whether blockade of K-ATP channels with glibenclamide abrogated the protective effect of GLP-1 in humans. METHODS Thirty-two non-diabetic patients awaiting stenting of the left anterior descending artery (LAD) were allocated into 4 groups (control, glibenclamide, GLP-1, and GLP-1 + glibenclamide). Glibenclamide was given orally prior to the procedure. A left ventricular conductance catheter recorded pressure-volume loops during a 1-min low-pressure balloon occlusion (BO1) of the LAD. GLP-1 or saline was then infused for 30-min followed by a further 1-min balloon occlusion (BO2). In a non-invasive study, 10 non-diabetic patients were randomized to receive two dobutamine stress echocardiograms (DSE) during GLP-1 infusion with or without oral glibenclamide pretreatment. RESULTS GLP-1 prevented stunning even with glibenclamide pretreatment; the Δ % dP/dtmax 30-min post-BO1 normalized to baseline after GLP-1: 0.3 ± 6.8 % (p = 0.02) and GLP-1 + glibenclamide: -0.8 ± 9.0 % (p = 0.04) compared to control: -11.5 ± 10.0 %. GLP-1 also reduced cumulative stunning after BO2: -12.8 ± 10.5 % (p = 0.02) as did GLP-1 + glibenclamide: -14.9 ± 9.2 % (p = 0.02) compared to control: -25.7 ± 9.6 %. Glibenclamide alone was no different to control. Glibenclamide pretreatment did not affect global or regional systolic function after GLP-1 at peak DSE stress (EF 74.6 ± 6.4 vs. 74.0 ± 8.0, p = 0.76) or recovery (EF 61.9 ± 5.7 vs. 61.4 ± 5.6, p = 0.74). CONCLUSIONS Glibenclamide pretreatment does not abrogate the protective effect of GLP-1 in human models of non-lethal myocardial ischemia. Trial registration Clinicaltrials.gov Unique Identifier: NCT02128022.