Mutations in the Kv1.5 channel gene KCNA5 in cardiac arrest patients
ABSTRACT Mutations in one of the ion channels shaping the cardiac action potential can lead to action potential prolongation. However, only in a minority of cardiac arrest cases mutations in the known arrhythmia-related genes can be identified. In two patients with arrhythmia and cardiac arrest, we identified the point mutations P91L and E33V in the KCNA5 gene encoding the Kv1.5 potassium channel that has not previously been associated with arrhythmia. We functionally characterized the mutations in HEK293 cells. The mutated channels behaved similarly to the wild-type with respect to biophysical characteristics and drug sensitivity. Both patients also carried a D85N polymorphism in KCNE1, which was neither found to influence the Kv1.5 nor the Kv7.1 channel activity. We conclude that although the two N-terminal Kv1.5 mutations did not show any apparent electrophysiological phenotype, it is possible that they may influence other cellular mechanisms responsible for proper electrical behaviour of native cardiomyocytes.
SourceAvailable from: Nirakar Sahoo[Show abstract] [Hide abstract]
ABSTRACT: Significance: Voltage-gated K+ channels are a large family of K+-selective ion channel protein complexes that open on membrane depolarization. These K+ channels are expressed in diverse tissues and their function is vital for numerous physiological processes, in particular of neurons and muscle cells. Potentially reversible oxidative regulation of voltage-gated K+ channels by reactive species such as ROS (reactive oxygen species) represents a contributing mechanism of normal cellular plasticity and may play important roles in diverse pathologies including neurodegenerative diseases. Recent Advances: Studies using various protocols of oxidative modification, site-directed mutagenesis, and structural and kinetic modeling are providing a broader phenomenology and emerging mechanistic insights. Critical Issues: Physicochemical mechanisms of the functional consequences of oxidative modifications of voltage-gated K+ channels are only beginning to be revealed. In vivo documentation of oxidative modifications of specific amino-acid residues of various voltage-gated K+ channel proteins, including the target specificity issue, is largely absent. Future Directions: High-resolution chemical and proteomic analysis of ion channel proteins with respect to oxidative modification combined with ongoing studies on channel structure and function will provide a better understanding of how the function of voltage-gated K+ channels is tuned by ROS and the corresponding reducing enzymes to meet cellular needs.Antioxidants & Redox Signaling 09/2013; DOI:10.1089/ars.2013.5614 · 7.67 Impact Factor
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ABSTRACT: Postmortem genetic testing (molecular autopsy) for the common long QT syndrome (LQTS) and catecholaminergic polymorphic ventricular tachycardia (CPVT) genes reveals a pathogenic mutation in up to 30% of sudden unexplained death (SUD). The role of additional cardiac arrhythmia and cardiomyopathy genes in SUD is largely unknown. To investigate the feasibility and outcomes of performing exome sequencing based molecular autopsies in a cohort of consecutive SUD cases. Autopsies performed from 2005-2009 were reviewed for SUD. Postmortem blood was collected, DNA was isolated, and whole exome sequencing performed. Rare sequence variants in cardiac arrhythmia and cardiomyopathy genes were sought. There were 50 SUD cases, aged 1 to 40 years (mean 21.7 ±12 years), in the 5-year period, with a male predominance (1.9:1). The most common event at death was 'sleep' (48%). Exome sequencing in a subgroup of 28 SUD cases revealed 3 rare variations in 3 SUD cases (10%; 2 from exome sequencing and one from previous Sanger sequencing) in the common LQTS genes: a splice site variation and a single base deletion in KCNH2, and a missense variation in KCNQ1. Six rare variations in an additional 25 common genes of cardiac arrhythmias and cardiomyopathies were identified in 6 SUD (21%). Exome sequencing based molecular autopsy is a useful strategy as part of the investigation of SUD cases. The findings further expand the role of the molecular autopsy in both identifying a cause of death in the decedent, and in the evaluation of at-risk family relatives.Heart rhythm: the official journal of the Heart Rhythm Society 01/2014; DOI:10.1016/j.hrthm.2014.01.017 · 4.92 Impact Factor
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ABSTRACT: human Ether-à-go-go-Related Gene (hERG) encodes the pore-forming subunit of cardiac rapid delayed rectifier K(+) current (I Kr) channels, which play important roles in ventricular repolarization, in protecting the myocardium from unwanted premature stimuli, and in drug-induced Long QT Syndrome (LQTS). KCNE1, a small transmembrane protein, can coassemble with hERG. However, it is not known how KCNE1 variants influence the channel's response to premature stimuli or if they influence the sensitivity of hERG to pharmacological inhibition. Accordingly, whole-cell patch-clamp measurements of hERG current (I hERG) were made at 37°C from hERG channels coexpressed with either wild-type (WT) KCNE1 or with one of three KCNE1 variants (A8V, D76N, and D85N). Under both conventional voltage clamp and ventricular action potential (AP) clamp, the amplitude of I hERG was smaller for A8V, D76N, and D85N KCNE1 + hERG than for WT KCNE1 + hERG. Using paired AP commands, with the second AP waveform applied at varying time intervals following the first to mimic premature ventricular excitation, the response of I hERG carried by each KCNE1 variant was reduced compared to that with WT KCNE1 + hERG. The I hERG blocking potency of the antiarrhythmic drug quinidine was similar between WT KCNE1 and the three KCNE1 variants. However, the I hERG inhibitory potency of the antibiotic clarithromycin and of the prokinetic drug cisapride was altered by KCNE1 variants. These results demonstrate that naturally occurring KCNE1 variants can reduce the response of hERG channels to premature excitation and also alter the sensitivity of hERG channels to inhibition by some drugs linked to acquired LQTS.11/2013; 1(6):e00175. DOI:10.1002/phy2.175