- Article (3) (remove)
- N-terminal arginines modulate plasma-membrane localization of Kv7.1/KCNE1 channel complexes (2011)
- Background and Objective: The slow delayed rectifier current (IKs) is important for cardiac action potential termination. The underlying channel is composed of Kv7.1 α-subunits and KCNE1 β-subunits. While most evidence suggests a role of KCNE1 transmembrane domain and C-terminus for the interaction, the N-terminal KCNE1 polymorphism 38G is associated with reduced IKs and atrial fibrillation (a human arrhythmia). Structure-function relationship of the KCNE1 N-terminus for IKs modulation is poorly understood and was subject of this study. Methods: We studied N-terminal KCNE1 constructs disrupting structurally important positively charged amino-acids (arginines) at positions 32, 33, 36 as well as KCNE1 constructs that modify position 38 including an N-terminal truncation mutation. Experimental procedures included molecular cloning, patch-clamp recording, protein biochemistry, real-time-PCR and confocal microscopy. Results: All KCNE1 constructs physically interacted with Kv7.1. IKs resulting from co-expression of Kv7.1 with non-atrial fibrillation ‘38S’ was greater than with any other construct. Ionic currents resulting from co-transfection of a KCNE1 mutant with arginine substitutions (‘38G-3xA’) were comparable to currents evoked from cells transfected with an N-terminally truncated KCNE1-construct (‘Δ1-38’). Western-blots from plasma-membrane preparations and confocal images consistently showed a greater amount of Kv7.1 protein at the plasma-membrane in cells co-transfected with the non-atrial fibrillation KCNE1-38S than with any other construct. Conclusions: The results of our study indicate that N-terminal arginines in positions 32, 33, 36 of KCNE1 are important for reconstitution of IKs. Furthermore, our results hint towards a role of these N-terminal amino-acids in membrane representation of the delayed rectifier channel complex.
- Elevated Heart Rate Triggers Action Potential Alternans and Sudden Death. Translational Study of a Homozygous KCNH2 Mutation (2014)
- Background: Long QT syndrome (LQTS) leads to arrhythmic events and increased risk for sudden cardiac death (SCD). Homozygous KCNH2 mutations underlying LQTS-2 have previously been termed “human HERG knockout” and typically express severe phenotypes. We studied genotype-phenotype correlations of an LQTS type 2 mutation identified in the homozygous index patient from a consanguineous Turkish family after his brother died suddenly during febrile illness. Methods and Results: Clinical work-up, DNA sequencing, mutagenesis, cell culture, patch-clamp, in silico mathematical modelling, protein biochemistry, confocal microscopy were performed. Genetic analysis revealed a homozygous C-terminal KCNH2 mutation (p.R835Q) in the index patient (QTc ~506 ms with notched T waves). Parents were I° cousins – both heterozygous for the mutation and clinically unremarkable (QTc ~447 ms, father and ~396 ms, mother). Heterologous expression of KCNH2-R835Q showed mildly reduced current amplitudes. Biophysical properties of ionic currents were also only nominally changed with slight acceleration of deactivation and more negative V50 in R835Q-currents. Protein biochemistry and confocal microscopy revealed similar expression patterns and trafficking of WT and R835Q, even at elevated temperature. In silico analysis demonstrated mildly prolonged ventricular action potential duration (APD) compared to WT at a cycle length of 1000 ms. At a cycle length of 350 ms M-cell APD remained stable in WT, but displayed APD alternans in R835Q. Conclusion: Kv11.1 channels affected by the C-terminal R835Q mutation display mildly modified biophysical properties, but leads to M-cell APD alternans with elevated heart rate and could precipitate SCD under specific clinical circumstances associated with high heart rates.
- Risk stratification for sudden cardiac death: current status and challenges for the future (2014)
- Sudden cardiac death (SCD) remains a daunting problem. It is a major public health issue for several reasons: from its prevalence (20% of total mortality in the industrialized world) to the devastating psycho-social impact on society and on the families of victims often still in their prime, and it represents a challenge for medicine, and especially for cardiology. This text summarizes the discussions and opinions of a group of investigators with a long-standing interest in this field. We addressed the occurrence of SCD in individuals apparently healthy, in patients with heart disease and mild or severe cardiac dysfunction, and in those with genetically based arrhythmic diseases. Recognizing the need for more accurate registries of the global and regional distribution of SCD in these different categories, we focused on the assessment of risk for SCD in these four groups, looking at the significance of alterations in cardiac function, of signs of electrical instability identified by ECG abnormalities or by autonomic tests, and of the progressive impact of genetic screening. Special attention was given to the identification of areas of research more or less likely to provide useful information, and thereby more or less suitable for the investment of time and of research funds.