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.
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ABSTRACT: K(V)1.5, a voltage-gated potassium channel, has functional importance in regulating blood vessel tone and cardiac action potentials and is a target for numerous therapeutic drug development programs. Despite the importance of K(V)1.5, there is little knowledge of the mechanisms controlling expression of its underlying gene, Kcna5. We identified a 5' flanking region of the murine Kcna5 gene that drives expression of a luciferase reporter gene in primary smooth muscle cells and a smooth muscle cell line. The promoter contained CACCC nucleotide motifs, which we have shown to bind the Sp1 transcription factor in the aorta under physiological conditions in vivo. Inhibition of Sp1-Kcna5 promoter interactions using mithramycin A, a dominant-negative Sp1 mutant, or disruption of the CACCC boxes by mutagenesis inhibited promoter activity. Conversely, expression of exogenous Sp1 augmented promoter activity. Sp1 has known sensitivity to oxidative stress and, consistent with this property, Kcna5 promoter activity was suppressed by hydrogen peroxide-induced oxidative stress. Our results show that Kcna5 promoter activity in vascular smooth muscle is critically dependent on Sp1 regulation via CACCC box motifs and identify mechanisms that potentially influence the expression of K(V)1.5 channel expression in physiological or pathological conditions.AJP Heart and Circulatory Physiology 12/2007; 293(5):H2719-25. DOI:10.1152/ajpheart.00637.2007 · 4.01 Impact Factor
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ABSTRACT: Potassium channels are an extensive family of ion channels selectively permeable to potassium ions (K+). They serve important functions in many crucial physiological processes and their dysregulation is key in several pathophysiological states, including pulmonary arterial hypertension, cancer and cardiac arrhythmias. One subset of K+ channels is comprised of the voltage-gated K+ (Kv) channels, of which over 40 isoforms have been identified and shown to serve important roles in cellular processes, such as the maintenance of resting membrane potential, cell contractility, neuronal activity and cell proliferation. The Kv1.5 isoform, encoded by the KCNA5 gene, has received much attention, with extensive research already carried out into its physiological, biophysical, structural and molecular properties. It is believed to be a potential target in diseases such as atrial fibrillation and pulmonary hypertension. As a result, a wide variety of pathways and pharmacological tools/drugs with modulatory effects on this channel have been identified. This review focuses on inhibitory regulation of Kv1.5 channels and will outline the following aspects: 1) structure, sequence and function; 2) transcriptional regulation; 3) trafficking; 4) occlusion/inhibition; and 5) altered kinetics or biophysical properties.Drugs of the Future 01/2008; 33(1). DOI:10.1358/dof.2008.033.01.1177607 · 0.25 Impact Factor
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ABSTRACT: The ultra-rapid delayed rectifier potassium current (I(Kur)), encoded by Kv1.5 gene, is the critical determinant of Phase I repolarization of action potential duration (APD). The evidences that Kv1.5 gene expresses more extensively in human atrial myocytes than in ventricle and the I(Kur) currents has not been recorded in the human ventricle, suggest Kv1.5 potassium channel as a selective target for the treatment of atrial fibrillation (AF). Recent mutagenesis studies have provided us some evidences that are useful in designing Kv1.5 blockers. In order to further evaluate these molecular biological information, the homology model of Kv1.5 potassium channel was established based on the Kv1.2 crystal structure (PDB entry: 2A79) using MODELLER 9v2 program. After the molecular dynamics refinement, the optimized homology model was assessed as a reliable structure by PROCHECK, ERRAT, WHAT-IF, PROSA2003 and DOPE graph. The results of molecular docking studies on different Kv1.5 inhibitors are in agreement with the published mutagenesis data. Based on the docking conformations, a pharmacophore model was developed by HipHop algorithm in order to probe the common features of blockers. By analyzing the results, active site architecture, certain key residues and pharmacophore common-features that are responsible for substrate specificity were identified on the Kv1.5 potassium channel, which would be very helpful in understanding the blockade mechanism of Kv1.5 potassium channel and providing insights into rational design of novel Kv1.5 blockers.Journal of molecular graphics & modelling 05/2008; 27(2):178-87. DOI:10.1016/j.jmgm.2008.04.002 · 2.02 Impact Factor