The transverse-axial tubular system (tubular system) of cardiomyocytes plays a key role in excitation-contraction coupling. To determine the area of the tubular membrane in relation to the area of the surface membrane, indirect measurements through the determination of membrane capacitances are currently used in addition to microscopic methods. Unlike existing electrophysiological methods based on an irreversible procedure (osmotic shock), the proposed new approach uses a reversible short-term intermittent increase in the electrical resistance of the extracellular medium. The resulting increase in the lumen resistance of the tubular system makes it possible to determine separate capacitances of the tubular and surface membranes. Based on the analysis of the time course of the capacitive current, computational relations were derived to quantify the elements of the electrical equivalent circuit of the measured cardiomyocyte including both capacitances. The exposition to isotonic low-conductivity sucrose solution is reversible which is the main advantage of the proposed approach allowing repetitive measurements on the same cell under control and sucrose solutions. Experiments on rat ventricular cardiomyocytes (n = 20) resulted in the surface and tubular capacitance values implying the fraction of tubular capacitance/area of 0.327 ± 0.018. We conclude that the newly proposed method provides results comparable to the data obtained by the currently used detubulation method and, in addition, by being reversible, allows repeated evaluation of surface and tubular membrane parameters on the same cell.
- MeSH
- biologický transport * fyziologie MeSH
- buněčná membrána fyziologie MeSH
- iontové kanály řízené ligandy fyziologie MeSH
- lidé MeSH
- membránové transportní proteiny MeSH
- Check Tag
- lidé MeSH
- Publikační typ
- přehledy MeSH
The transverse-axial tubular system (t-tubules) plays an essential role in excitation-contraction coupling in cardiomyocytes. Its remodelling is associated with various cardiac diseases. Numerous attempts were made to analyse characteristics essential for proper understanding of the t-tubules and their impact on cardiac cell function in health and disease. The currently available methodical approaches related to the fraction of the t-tubular membrane area produce diverse data. The widely used detubulation techniques cause irreversible cell impairment, thus, distinct cell samples have to be used for estimation of t-tubular parameters in untreated and detubulated cells. Our proposed alternative method is reversible and allows repetitive estimation of the fraction of t-tubular membrane (ft) in cardiomyocytes using short-term perfusion of the measured cell with a low-conductive isotonic sucrose solution. It results in a substantial increase in the electrical resistance of t-tubular lumen, thus, electrically separating the surface and t-tubular membranes. Using the whole-cell patch-clamp measurement and the new approach in enzymatically isolated rat atrial and ventricular myocytes, a set of data was measured and evaluated. The analysis of the electrical equivalent circuit resulted in the establishment of criteria for excluding measurements in which perfusion with a low conductivity solution did not affect the entire cell surface. As expected, the final average ft in ventricular myocytes (0.337 ± 0.017) was significantly higher than that in atrial myocytes (0.144 ± 0.015). The parameter ft could be estimated repetitively in a particular cell (0.345 ± 0.021 and 0.347 ± 0.023 in ventricular myocytes during the first and second sucrose perfusion, respectively). The new method is fast, simple, and leaves the measured cell intact. It can be applied in the course of experiments for which it is useful to estimate both the surface and t-tubular capacitance/area in a particular cell.
- Publikační typ
- časopisecké články MeSH
Bronchodilator aminophylline may induce atrial or less often ventricular arrhythmias. The mechanism of this proarrhythmic side effect has not been fully explained. Modifications of inward rectifier potassium (Kir) currents including IK1 are known to play an important role in arrhythmogenesis; however, no data on the aminophylline effect on these currents have been published. Hence, we tested the effect of aminophylline (3-100 μM) on IK1 in enzymatically isolated rat ventricular myocytes using the whole-cell patch-clamp technique. A dual steady-state effect of aminophylline was observed; either inhibition or activation was apparent in individual cells during the application of aminophylline at a given concentration. The smaller the magnitude of the control IK1, the more likely the activation of the current by aminophylline and vice versa. The effect was reversible; the relative changes at -50 and -110 mV did not differ. Using IK1 channel population model, the dual effect was explained by the interaction of aminophylline with two different channel populations, the first one being inhibited and the second one being activated. Considering various fractions of these two channel populations in individual cells, varying effects observed in the measured cells could be simulated. We propose that the dual aminophylline effect may be related to the direct and indirect effect of the drug on various Kir2.x subunits forming the homo- and heterotetrameric IK1 channels in a single cell. The observed IK1 changes induced by clinically relevant concentrations of aminophylline might contribute to arrhythmogenesis related to the use of this bronchodilator in clinical medicine.
- MeSH
- aminofylin škodlivé účinky MeSH
- bronchodilatancia škodlivé účinky MeSH
- draslík farmakologie MeSH
- draslíkové kanály dovnitř usměrňující * MeSH
- kardiomyocyty fyziologie MeSH
- krysa rodu rattus MeSH
- srdeční arytmie MeSH
- zvířata MeSH
- Check Tag
- krysa rodu rattus MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Amputací na horní končetině dochází ke vzniku asymetrie v rozložení hmotnosti těla, která se projevuje ve změnách polohy vybraných segmentů a z toho plynoucích odchylkách v držení těla. Mění se statika osového systému, zvyšují se nároky na posturální stabilitu. U osob s amputací na horní končetině roste riziko pádů. Důležitým faktorem pro zmenšení těchto negativních změn je používání vhodné protézy, která pozitivně ovlivňuje dynamickou lokomoční stabilitu. Cílem studie bylo určit vliv protézy na posturu a její stabilitu v bipedálním stoji u osob s amputací na horní končetině. Dvanáct osob (věk 50,6 ± 18,5 roku; doba užívání protézy 21,3 ± 19,1 roku) s jednostrannou amputací na horní končetině absolvovalo hodnocení postury (systém DTP-3) a posturální stability (dvě silové plošiny). Výsledky ukázaly, že při aplikaci protézy došlo v bipedálním stoji k zmenšení bederní lordózy a hrudní kyfózy. Použití protézy významně neovlivnilo úroveň posturální stability ve stoji s otevřenýma ani zavřenýma očima.
Upper limb amputation causes weight-bearing asymmetry, which leads to changes in body posture. Statics of the spine changes, postural control demands increase, and risk of falling rises. A suitable prosthesis which positively affects locomotor stability can help to mitigate these negative impacts of amputation. The aim of this study was to assess the effect of prosthesis on body posture and postural stability in upper limb amputees. Twelve persons with unilateral upper limb amputation (age 50.6 ± 18.5 years, time since amputation 21.3 ± 19.1 years) participated in the study. They underwent assessment of static posture (noninvasive 3D system DTP-3) and balance in quiet bipedal stance with eyes open and closed (two force plates) with and without a prosthesis. Wearing a prosthesis led to a decrease in lumbar lordosis and thoracic kyphosis; however, it did not significantly affect standing balance.
- MeSH
- amputace škodlivé účinky MeSH
- horní končetina * MeSH
- interpretace statistických dat MeSH
- lidé středního věku MeSH
- lidé MeSH
- postura těla fyziologie MeSH
- posturální rovnováha * fyziologie MeSH
- protézy a implantáty * MeSH
- senioři MeSH
- Check Tag
- lidé středního věku MeSH
- lidé MeSH
- mužské pohlaví MeSH
- senioři MeSH
- ženské pohlaví MeSH
- Publikační typ
- klinická studie 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
Nicotine abuse is associated with variety of diseases including arrhythmias, most often atrial fibrillation (AF). Altered inward rectifier potassium currents including acetylcholine-sensitive current I K(Ach) are known to be related to AF pathogenesis. Since relevant data are missing, we aimed to investigate I K(Ach) changes at clinically relevant concentrations of nicotine. Experiments were performed by the whole cell patch clamp technique at 23 ± 1 °C on isolated rat atrial myocytes. Nicotine was applied at following concentrations: 4, 40 and 400 nM; ethanol at 20 mM (∼0.09%). Nicotine at 40 and 400 nM significantly activated constitutively active component of I K(Ach) with the maximum effect at 40 nM (an increase by ∼100%); similar effect was observed at -110 and -50 mV. Changes at 4 nM nicotine were negligible on average. Coapplication of 40 nM nicotine and 20 mM ethanol (which is also known to activate this current) did not show cumulative effect. In the case of acetylcholine-induced component of I K(Ach), a dual effect of nicotine and its correlation with the current magnitude in control were apparent: the current was increased by nicotine in the cells showing small current in control and vice versa. The effect of 40 and 400 nM nicotine on acetylcholine-induced component of I K(Ach) was significantly different at -110 and -50 mV. We conclude that nicotine at clinically relevant concentrations significantly increased constitutively active component of I K(Ach) and showed a dual effect on its acetylcholine-induced component, similarly as ethanol. Synchronous application of nicotine and ethanol did not cause additive effect.
- MeSH
- acetylcholin farmakologie MeSH
- časové faktory MeSH
- dovnitř usměrňující draslíkové kanály spřažené s G proteiny agonisté účinky léků MeSH
- ethanol toxicita MeSH
- hodnocení rizik MeSH
- kardiomyocyty účinky léků metabolismus MeSH
- membránové potenciály MeSH
- nikotin toxicita MeSH
- potkani Wistar MeSH
- srdeční arytmie chemicky indukované metabolismus MeSH
- srdeční síně účinky léků metabolismus MeSH
- techniky in vitro MeSH
- vztah mezi dávkou a účinkem léčiva MeSH
- zvířata MeSH
- Check Tag
- mužské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
Alcohol consumption may result in electrocardiographic changes and arrhythmias, at least partly due to effects of ethanol on cardiac ionic currents. Contractility and intracellular Ca(2+) dynamics seem to be altered as well. In this study, we integrated the available (mostly animal) experimental data into previously published models of the rat and human ventricular myocytes to assess the share of ionic current components in ethanol-induced changes in AP configuration and cytosolic Ca(2+) transient in ventricular cardiomyocytes. The rat model reproduced well the experimentally observed changes in AP duration (APD) under ethanol (slight prolongation at 0.8 mM and shortening at ≥8 mM). These changes were almost exclusively caused by the ethanol-induced alterations of I K1. The cytosolic Ca(2+) transient decreased gradually with the increasing ethanol concentration as a result of the ethanol-induced inhibition of I Ca. In the human model, ethanol produced a dose-dependent APD lengthening, dominated by ethanol effect on I Kr, the key repolarising current in human ventricles. This effect might contribute to the clinically observed proarrhythmic effects of ethanol in predisposed individuals.
- MeSH
- akční potenciály účinky léků MeSH
- biologické modely MeSH
- ethanol farmakologie MeSH
- intracelulární prostor účinky léků metabolismus MeSH
- kardiomyocyty účinky léků metabolismus MeSH
- krysa rodu rattus MeSH
- lidé MeSH
- počítačová simulace * MeSH
- sarkoplazmatické retikulum účinky léků metabolismus MeSH
- srdeční komory cytologie MeSH
- vápník metabolismus MeSH
- zvířata MeSH
- Check Tag
- krysa rodu rattus MeSH
- lidé MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
- práce podpořená grantem MeSH
Atrial fibrillation is the most common arrhythmia at alcohol consumption. Its pathogenesis is complex, at least partly related to changes of cardiac inward rectifier potassium currents including IK1. Both ethanol and acetaldehyde have been demonstrated to considerably modify IK1 in rat ventricular myocytes. However, analogical data on the atrial IK1 are lacking. The present study aimed to analyse IK1 changes induced by ethanol and acetyldehyde in atrial myocytes. The experiments were performed by the whole cell patch-clamp technique at 23 ± 1°C on enzymatically isolated rat and guinea-pig atrial myocytes as well as on expressed human Kir2.3 channels. Ethanol (8 - 80 mM) caused a dual effect on the atrial IK1 showing the steady-state activation in some cells but inhibition in others in agreement with the ventricular data; on average, the activation was observed (at 20 mM by 4.3 and 4.5% in rat and guinea-pig atrial myocytes, respectively). The effect slightly increased with depolarization above -60 mV. In contrast, the current through human Kir2.3 channels (prevailing atrial IK1 subunit) was inhibited in all measured cells. Unlike ethanol, acetaldehyde (3 μM) markedly inhibited the rat atrial IK1 (by 15.1%) in a voltage-independent manner, comparably to the rat ventricular IK1. The concurrent application of ethanol (20 mM) and acetaldehyde (3 μM) resulted in the steady-state IK1 activation by 2.1% on average. We conclude that ethanol and even more acetaldehyde affected IK1 at clinically relevant concentrations if applied separately. Their combined effect did not significantly differ from the effect of ethanol alone.
- MeSH
- acetaldehyd farmakologie MeSH
- CHO buňky MeSH
- Cricetulus MeSH
- draslíkové kanály dovnitř usměrňující genetika fyziologie MeSH
- ethanol farmakologie MeSH
- kardiomyocyty účinky léků fyziologie MeSH
- krysa rodu rattus MeSH
- kultivované buňky MeSH
- lékové interakce MeSH
- lidé MeSH
- morčata MeSH
- potkani Wistar MeSH
- zvířata MeSH
- Check Tag
- krysa rodu rattus MeSH
- lidé MeSH
- morčata MeSH
- mužské pohlaví MeSH
- zvířata MeSH
- Publikační typ
- časopisecké články MeSH
