Mutations in genes encoding cardiac ionic channels and related proteins are identified in ~50% families with the long QT syndrome. Each family is usually characterized by its own mutation; the same mutation found in unrelated families living in the same region may represent the founder mutation. In our database, the same KCNQ1 mutation (c.926C>T; p.T309I-Kv7.1) was present in 5 putatively unrelated LQTS families. This project is aimed at verification of the hypothesis that T309I-Kv7.1 mutation is the founder mutation in our region. Using pedigree extension and genetic screening in T309I-Kv7.1 families, new mutation carriers will be identified and clinically investigated. The functional effect of the mutation will be revealed using biophysical analysis in wild type and mutant human IKs channels expressed in CHO cells, and mathematical simulations in a human ventricular cell model. These data will allow us to provide genotype and phenotype-guided therapeutic measures to prevent malignant arrhythmias and sudden cardiac death even in asymptomatic mutation carriers.

U ~50% rodin se syndromem dlouhého intervalu QT jsou nacházeny mutace v genech kódujících srdeční iontové kanály a související proteiny. Každá rodina má obvykle svou “vlastní” mutaci. Stejná mutace nacházená v nepříbuzných rodinách ze stejného regionu může představovat tzv. „founder mutation“. V naší databázi je stejná mutace c.926C>T; p.T309I-Kv7.1 genu KCNQ1přítomna v 5 nepříbuzných rodinách. Cílem projektu je potvrzení hypotézy, že mutace T309I-Kv7.1 představuje v našem regionu „founder mutation“. Rozšířením rodokmenů a genetickým screeningem v T309I-Kv7.1 rodinách budou identifikováni a klinicky vyšetření noví nosiči mutace. Funkční efekt mutace bude hodnocen biofyzikální analýzou u „wild type“ a mutovaného lidského IKs kanálu exprimovaného v CHO buňkách a matematickými simulacemi na lidskému modelu srdeční komorové buňky. Tato data umožní zavést genotypem a fenotypem řízená terapeutická opatření k prevenci maligních komorových arytmií a náhlé srdeční smrti i u asymptomatických nosičů mutace.

• MeSH
• detekce genetických nosičů MeSH
• draslíkový kanál KCNQ1 genetika   MeSH
• lidé MeSH
• metoda terčíkového zámku MeSH
• modely genetické MeSH
• modely kardiovaskulární MeSH
• mutace genetika   MeSH
• teoretické modely MeSH
• vápníkem aktivované draslíkové kanály se střední vodivostí genetika   MeSH
• Check Tag
• lidé MeSH

• Konspekt
• Patologie. Klinická medicína
• NLK Obory
• genetika, lékařská genetika
• kardiologie
• NLK Publikační typ
• závěrečné zprávy o řešení grantu AZV MZ ČR

The variant c.926C > T (p.T309I) in KCNQ1 gene was identified in 10 putatively unrelated Czech families with long QT syndrome (LQTS). Mutation carriers (24 heterozygous individuals) were more symptomatic compared to their non-affected relatives (17 individuals). The carriers showed a mild LQTS phenotype including a longer QTc interval at rest (466 ± 24 ms vs. 418 ± 20 ms) and after exercise (508 ± 32 ms vs. 417 ± 24 ms), 4 syncopes and 2 aborted cardiac arrests. The same haplotype associated with the c.926C > T variant was identified in all probands. Using the whole cell patch clamp technique and confocal microscopy, a complete loss of channel function was revealed in the homozygous setting, caused by an impaired channel trafficking. Dominant negativity with preserved reactivity to β-adrenergic stimulation was apparent in the heterozygous setting. In simulations on a human ventricular cell model, the dysfunction resulted in delayed afterdepolarizations (DADs) and premature action potentials under β-adrenergic stimulation that could be prevented by a slight inhibition of calcium current. We conclude that the KCNQ1 variant c.926C > T is the first identified LQTS-related founder mutation in Central Europe. The dominant negative channel dysfunction may lead to DADs under β-adrenergic stimulation. Inhibition of calcium current could be possible therapeutic strategy in LQTS1 patients refractory to β-blocker therapy.

• MeSH
• beta blokátory aplikace a dávkování   škodlivé účinky   MeSH
• detekce genetických nosičů MeSH
• dospělí MeSH
• draslíkový kanál KCNQ1 genetika   MeSH
• fenotyp MeSH
• genetická predispozice k nemoci * MeSH
• genetické asociační studie MeSH
• genotyp MeSH
• haplotypy genetika   MeSH
• heterozygot MeSH
• homozygot MeSH
• lidé MeSH
• mutace genetika   MeSH
• rodokmen MeSH
• syndrom dlouhého QT genetika   patologie   MeSH
• Check Tag
• dospělí MeSH
• lidé MeSH
• mužské pohlaví MeSH
• ženské pohlaví MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Geografické názvy
• Evropa MeSH

The current density (J) is a parameter routinely used to characterize individual ionic membrane currents. Its evaluation is based on the presumption that the magnitude of whole-cell ionic membrane current (I) is directly proportional to the cell membrane capacitance (C), i.e. I positively and strongly correlates with C and the regression line describing I-C relation intersects the y-axis close to the origin of coordinates. We aimed to prove the presumption in several examples and find whether the conversion of I to J could be always beneficial. I-C relation was analysed in several potassium currents, measured in rat atrial myocytes (in inward rectifier currents, IK1, and both the constitutively active and acetylcholine-induced components of acetylcholine-sensitive current, IK(Ach)CONST and IK(Ach)ACH), and in rat ventricular myocytes (transient outward current Ito). I-C correlation was estimated by the Pearson coefficient (r). A coefficient (k) was newly suggested describing deviation of the regression intercept from zero in currents with considerable r value. Based on mathematical simulations, I was satisfactorily proportional to C when r ≥ 0.6 and k ≤ 0.2 which was fulfilled in IK1 and IK(Ach)ACH (r = 0.84, k = 0.20, and r = 0.61, k = 0.06, respectively). I-C correlation was significantly positive, but weak in IK(Ach)CONST (r = 0.42), and virtually missing in Ito (r = 0.04). The impaired I-C proportionality in IK(Ach)CONST and Ito likely reflects heterogeneity of the channel expression. We conclude that the conversion of I to J should be avoided when I-C proportionality is absent. Otherwise, serious misinterpretation of data may arise.

• MeSH
• acetylcholin chemie   MeSH
• buněčná membrána fyziologie   MeSH
• elektrická kapacitance MeSH
• elektrofyziologie MeSH
• genotyp MeSH
• ionty MeSH
• kardiomyocyty účinky léků   MeSH
• krysa rodu rattus MeSH
• membránové potenciály účinky léků   MeSH
• myokard MeSH
• potkani Wistar MeSH
• srdeční síně patologie   MeSH
• svalové buňky cytologie   MeSH
• teoretické modely MeSH
• zvířata MeSH
• Check Tag
• krysa rodu rattus MeSH
• mužské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The distribution of data presented in many electrophysiological studies is presumed to be normal without any convincing evidence. To test this presumption, the cell membrane capacitance and magnitude of inward rectifier potassium currents were recorded by the whole-cell patch clamp technique in rat atrial myocytes. Statistical analysis of the data showed that these variables were not distributed normally. Instead, a positively skewed distribution appeared to be a better approximation of the real data distribution. Consequently, the arithmetic mean, used inappropriately in such data, may substantially overestimate the true mean value characterizing the central tendency of the data. Moreover, a large standard deviation describing the variance of positively skewed data allowed 95% confidence interval to include unrealistic negative values. We therefore conclude that the normality of the electrophysiological data should be tested in every experiment and, if rejected, the positively skewed data should be more accurately characterized by the median and interpercentile range or, if justified (namely in the case of log-normal and gamma data distribution), by the geometric mean and the geometric standard deviation.

• MeSH
• algoritmy MeSH
• buněčná membrána patologie   fyziologie   MeSH
• elektrická kapacitance MeSH
• elektrody MeSH
• elektrofyziologie metody   MeSH
• interpretace statistických dat MeSH
• krysa rodu rattus MeSH
• membránové potenciály MeSH
• normální rozdělení * MeSH
• potkani Wistar MeSH
• reprodukovatelnost výsledků MeSH
• srdeční síně patologie   MeSH
• svalové buňky fyziologie   MeSH
• teoretické modely MeSH
• zvířata MeSH
• Check Tag
• krysa rodu rattus MeSH
• mužské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

A variety of techniques of cell capacitance measurement have been proposed and applied in cellular electrophysiology. They are mostly based on the evaluation of membrane current responses to small changes in the membrane voltage. One of the currently used approaches applies the least-squares fit of an exponential current decay in response to voltage clamped rectangular pulses. In this study, we propose an alternative simpler approach to evaluation of the exponential parts in the current responses to square wave stimulation and present preliminary results of membrane capacitance evaluation. It is based on the property of the exponential function that has not yet been used to measure membrane capacitance. The time constant and the asymptote of the exponential waveform are unambiguously determined by the values read at three points separated by a constant time interval. In order to minimize the effect of noise and deviations from the exponential waveform, the triplet of points is designed to slide along the time axis. The results of the proposed approach and those previously evaluated by the least squares method are comparable. The method described may be advantageous for continuously recording changes in membrane capacitance.

• MeSH
• algoritmy MeSH
• elektrická kapacitance MeSH
• elektrická vodivost MeSH
• elektrofyziologie MeSH
• krysa rodu rattus MeSH
• membránové potenciály fyziologie   MeSH
• metoda nejmenších čtverců MeSH
• metoda terčíkového zámku metody   MeSH
• modely neurologické MeSH
• neurony MeSH
• počítačová simulace MeSH
• reprodukovatelnost výsledků MeSH
• software MeSH
• srdeční síně patologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu rattus MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The slow delayed rectifier potassium current (IKs) significantly contributes to cardiac repolarization under specific conditions, particularly at stimulation by the protein kinase A (PKA) during increased sympathetic tone. Impaired PKA-mediated stimulation of IKs channels may considerably aggravate dysfunction of the channels induced by mutations in the KCNQ1 gene that encodes the structure of the α-subunit of IKs channels. These mutations are associated with several subtypes of inherited arrhythmias, mainly long QT syndrome type 1, less commonly short QT syndrome type 2, and atrial fibrillation. The impaired PKA reactivity of IKs channels may significantly increase the risk of arrhythmia in these patients. Unfortunately, only approximately 2.7% of the KCNQ1 variants identified as putatively clinically significant have been studied with respect to this problem. This review summarizes the current knowledge in the field to stress the importance of the PKA-mediated regulation of IKs channels, and to appeal for further analysis of this regulation in KCNQ1 mutations associated with inherited arrhythmogenic syndromes. On the basis of the facts summarized in our review, we suggest several new regions of the α-subunit of the IKs channels as potential contributors to PKA stimulation, namely the S4 and S5 segments, and the S2-S3 and S4-S5 linkers. Deeper knowledge of mechanisms of the impaired PKA response in mutated IKs channels may help to better understand this regulation, and may improve risk stratification and management of patients suffering from related pathologies.

• MeSH
• beta-adrenergní receptory fyziologie   MeSH
• draslíkový kanál KCNQ1 genetika   MeSH
• fosforylace MeSH
• lidé MeSH
• mutace MeSH
• pozdní usměrňovače draslíkových kanálů fyziologie   MeSH
• převodní systém srdeční fyziologie   MeSH
• proteinkinasy závislé na cyklickém AMP fyziologie   MeSH
• syndrom dlouhého QT genetika   patofyziologie   MeSH
• Check Tag
• lidé MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• přehledy MeSH

Recent experimental work has revealed unusual features of the effect of certain drugs on cardiac inwardly rectifying potassium currents, including the constitutively active and acetylcholine-induced components of acetylcholine-sensitive current (IKAch). These unusual features have included alternating susceptibility of the current components to activation and inhibition induced by ethanol or nicotine applied at various concentrations, and significant correlation between the drug effect and the current magnitude measured under drug-free conditions. To explain these complex drug effects, we have developed a new type of quantitative model to offer a possible interpretation of the effect of ethanol and nicotine on the IKAch channels. The model is based on a description of IKAch as a sum of particular currents related to the populations of channels formed by identical assemblies of different α-subunits. Assuming two different channel populations in agreement with the two reported functional IKAch-channels (GIRK1/4 and GIRK4), the model was able to simulate all the above-mentioned characteristic features of drug-channel interactions and also the dispersion of the current measured in different cells. The formulation of our model equations allows the model to be incorporated easily into the existing integrative models of electrical activity of cardiac cells involving quantitative description of IKAch. We suppose that the model could also help make sense of certain observations related to the channels that do not show inward rectification. This new ionic channel model, based on a concept we call population type, may allow for the interpretation of complex interactions of drugs with ionic channels of various types, which cannot be done using the ionic channel models available so far.

• MeSH
• acetylcholin farmakologie   MeSH
• biologické modely MeSH
• časové faktory MeSH
• dovnitř usměrňující draslíkové kanály spřažené s G proteiny metabolismus   MeSH
• ethanol farmakologie   MeSH
• gating iontového kanálu účinky léků   MeSH
• nikotin farmakologie   MeSH
• počítačová simulace MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

Inward rectifier potassium currents (I Kir,x) belong to prominent ionic currents affecting both resting membrane voltage and action potential repolarization in cardiomyocytes. In existing integrative models of electrical activity of cardiac cells, they have been described as single current components. The proposed quantitative model complies with findings indicating that these channels are formed by various homomeric or heteromeric assemblies of channel subunits with specific functional properties. Each I Kir,x may be expressed as a total of independent currents via individual populations of identical channels, i.e., channels formed by the same combination of their subunits. Solution of the model equations simulated well recently observed unique manifestations of dual ethanol effect in rat ventricular and atrial cells. The model reflects reported occurrence of at least two binding sites for ethanol within I Kir,x channels related to slow allosteric conformation changes governing channel conductance and inducing current activation or inhibition. Our new model may considerably improve the existing models of cardiac cells by including the model equations proposed here in the particular case of the voltage-independent drug-channel interaction. Such improved integrative models may provide more precise and, thus, more physiologically relevant results.

• MeSH
• akční potenciály * MeSH
• alosterická regulace MeSH
• draslíkové kanály dovnitř usměrňující chemie   metabolismus   MeSH
• ethanol farmakologie   MeSH
• kardiomyocyty účinky léků   metabolismus   fyziologie   MeSH
• krysa rodu rattus MeSH
• modely kardiovaskulární MeSH
• multimerizace proteinu MeSH
• srdce - funkce komor MeSH
• srdeční komory cytologie   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu rattus MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH

The ratio of densities of Na-Ca exchanger current (INaCa) in the t-tubular and surface membranes (INaCa-ratio) computed from the values of INaCa and membrane capacitances (Cm) measured in adult rat ventricular cardiomyocytes before and after detubulation ranges between 1.7 and 25 (potentially even 40). Variations of action potential waveform and of calcium turnover within this span of the INaCa-ratio were simulated employing previously developed model of rat ventricular cell incorporating separate description of ion transport systems in the t-tubular and surface membranes. The increase of INaCa-ratio from 1.7 to 25 caused a prolongation of APD (duration of action potential at 90% repolarisation) by 12, 9, and 6% and an increase of peak intracellular Ca(2+) transient by 45, 19, and 6% at 0.1, 1, and 5 Hz, respectively. The prolonged APD resulted from the increase of INaCa due to the exposure of a larger fraction of Na-Ca exchangers to higher Ca(2+) transients under the t-tubular membrane. The accompanying rise of Ca(2+) transient was a consequence of a higher Ca(2+) load in sarcoplasmic reticulum induced by the increased Ca(2+) cycling between the surface and t-tubular membranes. However, the reason for large differences in the INaCa-ratio assessed from measurements in adult rat cardiomyocytes remains to be explained.

• MeSH
• buněčná membrána metabolismus   MeSH
• kardiomyocyty metabolismus   MeSH
• krysa rodu rattus MeSH
• membránové potenciály fyziologie   MeSH
• modely kardiovaskulární * MeSH
• sodík metabolismus   MeSH
• srdeční komory metabolismus   MeSH
• vápník metabolismus   MeSH
• zvířata MeSH
• Check Tag
• krysa rodu rattus MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH