Ultrashort Bradycardic Effect of Newly Synthesized Compounds

Changes in the heart rate induced by four different doses of two newly synthesized potential ultrashort-action antagonists of beta adrenergic receptors were tested in 90 male laboratory Wistar rats. The isoprenaline-induced tachycardia model was used. Their effects were compared with those of esmolol. In the second part of the study, approximate electro-physiological measurements were made in vitro to assess the influence of the compounds tested on ion membrane currents in isolated ventricular cardiomyocytes. Both compounds demonstrated significant bradycardic effects in all concentrations tested compared with the control group, but they differed in the time of the onset of their action. Both newly synthesized compounds induced blockade of the fast sodium current (INa) and potassium currents (Ito, IK1, IK,end)

Blokáda sodíkového a přechodného draslíkového proudu perfenazinem: experimentální a simulační studie

The effect of a neuroleptic drug perphenazine on sodium current INa and transient outward potassium current Ito was studied in rat ventricular myocytes at room temperature. Perphenazine reversibly blocked INa (reducing its amplitude; IC50 = 1.24 +/- 0.10 μmol/l, nH =0.99 +/- 0.08) and Ito (accelerating its apparent inactivation with a slight decrease of its amplitude; IC50 = 38.2 +/- 3.5 μmol/l, nH = 0.75 +/- 0.07, evaluated from the changes of time integral). Both INa- and Ito-block was use- and frequency-dependent (20%-increase of INablock and 10%-increase of Ito-block under 0.3 and 10 μmol/l perphenazine, respectively, at the stimulation frequency of 3.3 Hz applied after a 15-s rest). The results of quantitative modelling suggest that perphenazine interacts with INa-channels in inactivated states, and with Ito-channels in both open and open-inactivated states

Účinek perphenazinu na přechodný draslíkový proud u komorových buněk potkana

The aim of this study was to explore the effect of a phenothiazine neuroleptic drug perphenazine on transient outward potassium current Ito in rat ventricular myocytes. Perphenazine reversibly decreased the amplitude and accelerated the apparent inactivation of Ito in a concentration-dependent manner with EC50 = 26.4 +/- 3.5 µmol/l and Hill coefficient n = 0.84 +/- 0.10 (evaluated from changes of time integral of Ito). Time course of Ito-inactivation was well fitted by a double exponential function; the fast time constant was significantly decreased under the effect of perphenazine and its concentration dependence was comparable with the concentration dependence of Ito-block represented by time integrals (EC50 = 26.8 +/- 8.2 µmol/l, n = 0.88 +/- 0.28). It is suggested that perphenazine-induced block via open channel is very likely involved in the mechanism of drug-channel interaction

Acute effects of alcohol on cardiac electrophysiology and arrhythmogenesis:Insights from multiscale in silico analyses

Acute excessive ethyl alcohol (ethanol) consumption alters cardiac electrophysiology and can evoke cardiac arrhythmias, e.g., in 'holiday heart syndrome'. Ethanol acutely modulates numerous targets in cardiomyocytes, including ion channels, calcium-handling proteins and gap junctions. However, the mechanisms underlying ethanol-induced arrhythmogenesis remain incompletely understood and difficult to study experimentally due to the multiple electrophysiological targets involved and their potential interactions with preexisting electrophysiological or structural substrates. Here, we employed cellular- and tissue-level in-silico analyses to characterize the acute effects of ethanol on cardiac electrophysiology and arrhythmogenesis. Acute electrophysiological effects of ethanol were incorporated into human atrial and ventricular cardiomyocyte computer models: reduced INa, ICa,L, Ito, IKr and IKur, dual effects on IK1 and IK,ACh (inhibition at low and augmentation at high concentrations), and increased INCX and SR Ca2+ leak. Multiscale simulations in the absence or presence of preexistent atrial fibrillation or heart-failure-related remodeling demonstrated that low ethanol concentrations prolonged atrial action-potential duration (APD) without effects on ventricular APD. Conversely, high ethanol concentrations abbreviated atrial APD and prolonged ventricular APD. High ethanol concentrations promoted reentry in tissue simulations, but the extent of reentry promotion was dependent on the presence of altered intercellular coupling, and the degree, type, and pattern of fibrosis. Taken together, these data provide novel mechanistic insight into the potential proarrhythmic interactions between a preexisting substrate and acute changes in cardiac electrophysiology. In particular, acute ethanol exposure has concentration-dependent electrophysiological effects that differ between atria and ventricles, and between healthy and diseased hearts. Low concentrations of ethanol can have anti-fibrillatory effects in atria, whereas high concentrations promote the inducibility and maintenance of reentrant atrial and ventricular arrhythmias, supporting a role for limiting alcohol intake as part of cardiac arrhythmia management.</p

Subepicardial phase 0 block and discontinuous transmural conduction underlie right precordial ST-segment elevation by a SCN5A loss-of-function mutation

Two mechanisms are generally proposed to explain right precordial ST-segment elevation in Brugada syndrome: 1) right ventricular (RV) subepicardial action potential shortening and/or loss of dome causing transmural dispersion of repolarization; and 2) RV conduction delay. Here we report novel mechanistic insights into ST-segment elevation associated with a Na+ current (INa) loss-of-function mutation from studies in a Dutch kindred with the COOH-terminal SCN5A variant p.Phe2004Leu. The proband, a man, experienced syncope at age 22 yr and had coved-type ST-segment elevations in ECG leads V1 and V2 and negative T waves in V2. Peak and persistent mutant INa were significantly decreased. INa closed-state inactivation was increased, slow inactivation accelerated, and recovery from inactivation delayed. Computer-simulated INa-dependent excitation was decremental from endo- to epicardium at cycle length 1,000 ms, not at cycle length 300 ms. Propagation was discontinuous across the midmyocardial to epicardial transition region, exhibiting a long local delay due to phase 0 block. Beyond this region, axial excitatory current was provided by phase 2 (dome) of the M-cell action potentials and depended on L-type Ca2+ current (“phase 2 conduction”). These results explain right precordial ST-segment elevation on the basis of RV transmural gradients of membrane potentials during early repolarization caused by discontinuous conduction. The late slow-upstroke action potentials at the subepicardium produce T-wave inversion in the computed ECG waveform, in line with the clinical ECG