Electrophysiological characterization of the hERG R56Q LQTS variant and targeted rescue by the activator RPR260243

Human Ether-à-go-go (hERG) channels contribute to cardiac repolarization, and inherited variants or drug block are associated with long QT syndrome type 2 (LQTS2) and arrhythmia. Therefore, hERG activator compounds present a therapeutic opportunity for targeted treatment of LQTS. However, a limiting concern is over-activation of hERG resurgent current during the action potential and abbreviated repolarization. Activators that slow deactivation gating (type I), such as RPR260243, may enhance repolarizing hERG current during the refractory period, thus ameliorating arrhythmogenicity with reduced early repolarization risk. Here, we show that, at physiological temperature, RPR260243 enhances hERG channel repolarizing currents conducted in the refractory period in response to premature depolarizations. This occurs with little effect on the resurgent hERG current during the action potential. The effects of RPR260243 were particularly evident in LQTS2-associated R56Q mutant channels, whereby RPR260243 restored WT-like repolarizing drive in the early refractory period and diastolic interval, combating attenuated protective currents. In silico kinetic modeling of channel gating predicted little effect of the R56Q mutation on hERG current conducted during the action potential and a reduced repolarizing protection against afterdepolarizations in the refractory period and diastolic interval, particularly at higher pacing rates. These simulations predicted partial rescue from the arrhythmic effects of R56Q by RPR260243 without risk of early repolarization. Our findings demonstrate that the pathogenicity of some hERG variants may result from reduced repolarizing protection during the refractory period and diastolic interval with limited effect on action potential duration, and that the hERG channel activator RPR260243 may provide targeted antiarrhythmic potential in these cases.

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Probucol-induced hERG Channel Reduction can be Rescued by Matrine and Oxymatrinein vitro

Current Pharmaceutical Design ◽

10.2174/1381612825666191026170033 ◽

2020 ◽

Vol 25 (43) ◽

pp. 4606-4612 ◽

Cited By ~ 1

Author(s):

Yuan-Qi Shi ◽

Pan Fan ◽

Guo-Cui Zhang ◽

Yu-Hao Zhang ◽

Ming-Zhu Li ◽

...

Keyword(s):

Action Potential ◽

Action Potential Duration ◽

Surface Expression ◽

Herg Channel ◽

Delayed Rectifier ◽

Patch Clamp Recording ◽

Herg Current ◽

Factor Specificity ◽

Lowering Drug

Background: The human ether-a-go-go-related gene (hERG) potassium channel is the rapidly activating component of cardiac delayed rectifier potassium current (IKr), which is a crucial determinant of cardiac repolarization. The reduction of hERG current is commonly believed to cause Long QT Syndrome (LQTs). Probucol, a cholesterol-lowering drug, induces LQTs by inhibiting the expression of the hERG channel. Unfortunately, there is currently no effective therapeutic method to rescue probucol-induced LQTs. Methods: Patch-clamp recording techniques were used to detect the action potential duration (APD) and current of hERG. Western blot was performed to measure the expression levels of proteins. Results: In this study, we demonstrated that 1 μM matrine and oxymatrine could rescue the hERG current and hERG surface expression inhibited by probucol. In addition, matrine and oxymatrine significantly shortened the prolonged action potential duration induced by probucol in neonatal cardiac myocytes. We proposed a novel mechanism underlying the probucol induced decrease in the expression of transcription factor Specificity protein 1 (Sp1), which is an established transactivator of the hERG gene. We also demonstrated that matrine and oxymatrine were able to upregulate Sp1 expression which may be one of the possible mechanisms by which matrine and oxymatrine rescued probucol-induced hERG channel deficiency. Conclusion: Our current results demonstrate that matrine and oxymatrine could rescue probucol-induced hERG deficiency in vitro, which may lead to potentially effective therapeutic drugs for treating acquired LQT2 by probucol in the future.

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Study of the Characteristics of the Pulmonary Vein and Superior Vena Cava of Rabbits

Journal of Biomaterials and Tissue Engineering ◽

10.1166/jbt.2021.2585 ◽

2021 ◽

Vol 11 (1) ◽

pp. 112-122

Author(s):

Pan Wang ◽

Xin-Chun Yang ◽

Xiu-Lan Liu ◽

Rong-Feng Bao ◽

Huai-Yu Ding ◽

...

Keyword(s):

Action Potential ◽

Pulmonary Vein ◽

Refractory Period ◽

Potassium Current ◽

Superior Vena ◽

Vena Cava ◽

Current Intensity ◽

Left And Right ◽

The Difference ◽

Right Atria

Background: This study aims to (1) investigate the characteristics of the action potential and triggering activity of cardiomyocytes in the pulmonary vein (PV) and superior vena cava (SVC) of rabbits and (2) study the features of cation currents in cardiomyocytes in rabbit PV and SVC-inward rectifier potassium current (IK1), transient outward potassium current (Ito), and non-selective cation currents (INSCC). Methods: The standard glass microelectrode and whole-cell patch-clamp techniques were used to record the action potential and various currents in the above cells. Results: (1) Cardiomyocytes in either PV or SVC had longer action potential durations than in the adjacent atrium, and spontaneous early after depolarization (EAD) could occur in both PV and SVC under normal physiological conditions. (2) The action potential in PV cardiomyocytes had a relative refractory period but did not have an absolute refractory period, and this characteristic enabled a premature beat that triggered a second plateau response, which led to EAD. (3) INSCC was found for the first time in the PV, SVC, and atria. (4) The current intensity of IK1, Ito, and INSCC was significantly lower in the PV and SVC than in the left and right atria, and the difference in the current intensity in INSCC could influence the action potential. Conclusions: PV and SVC can both initiate and maintain AF, but PV is the primary ectopic foci in initiating AF. The present study found that the second plateau response was easily induced in cardiomyocytes in PA shortly after depolarization. This was a specific characteristic of the action potential of PV. In addition, we preliminarily analyzed the differences in the main outward currents and noted a voltage-dependent INSCC in both PV and SVC rabbits’ cardiomyocytes. Furthermore, the current intensities of IK1, Ito, and INSCC were significantly lower in the PV and SVC than in the left and right atria, and the difference in the current intensity of INSCC influenced the action potential. The different permeability of INSCC for cations at different phases may play a role in inducing EAD.

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Prolongation of monophasic action potential duration and the refractory period in the human heart by tedisamil, a new potassium-blocking agent

European Heart Journal ◽

10.1093/oxfordjournals.eurheartj.a060403 ◽

1994 ◽

Vol 15 (10) ◽

pp. 1409-1414 ◽

Cited By ~ 23

Author(s):

K. BARGHEER ◽

F. BODE ◽

H. U. KLEIN ◽

H. J. TRAPPE ◽

M. R. FRANZ ◽

...

Keyword(s):

Action Potential ◽

Action Potential Duration ◽

Refractory Period ◽

Human Heart ◽

Blocking Agent ◽

Monophasic Action Potential

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Electrophysiological Characteristics of Classes of Neuron in the HVc of the Zebra Finch

Journal of Neurophysiology ◽

10.1152/jn.1998.80.2.914 ◽

1998 ◽

Vol 80 (2) ◽

pp. 914-923 ◽

Cited By ~ 36

Author(s):

Michinori Kubota ◽

Ikuo Taniguchi

Keyword(s):

Action Potential ◽

Zebra Finch ◽

Action Potential Duration ◽

The Other ◽

Time Dependent ◽

Inward Rectification ◽

Type I ◽

Type Ii ◽

Type Iii ◽

Type Iv

Kubota, Michinori and Ikuo Taniguchi. Electrophysiological characteristics of classes of neuron in the HVc of the zebra finch. J. Neurophysiol. 80: 914–923, 1998. Whole cell recordings were made from zebra finch HVc neurons in slice preparations. Four distinct classes of neuron were found on the basis of their electrophysiological properties. The morphological characteristics of some of these neurons were also examined by intracellular injection of Lucifer yellow. Type I neurons (21 of 65 cells) had longer time-to-peak of an afterhyperpolarization following an action potential than the other classes. They exhibited both fast and time-dependent inward rectification and an initial high-frequency firing followed by a slower constant firing. Type I neurons had large somata and thick dendrites with many spines. The axons of some of the neurons in this class projected in the direction of area X of the parolfactory lobe. Type II neurons (30 of 65 cells) had a more negative resting membrane potential than the other classes. They exhibited fast inward rectification. Type II neurons could be divided into two subclasses by the absence (IIa; 22 cells) and the presence (IIb; 8 cells) of a low-threshold transient depolarization. Type IIa neurons had relatively small somata and thin, spiny dendrites. The axons of some of the neurons in this class projected in the direction of the robust nucleus of the archistriatum (RA). Type IIb neurons had relatively large somata and thick dendrites with many spines. Type III neurons (6 of 65 cells) had a shorter action-potential duration than the other classes. They exhibited prominent time-dependent inward rectification and a regular tonic firing with little or no accommodation. Type III neurons had beaded, aspiny dendrites. Type IV neurons (8 of 65 cells) had a longer action-potential duration, a much larger input resistance, and longer membrane time constant than the other classes. Type IV neurons had small somata and thin, short, sparsely spiny dendrites. The axons of some of the neurons in this class projected in the direction of the RA. These classes of neuron may play distinct roles in song production and representation in the HVc.

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CHARACTERIZATION OF SIGNAL CONDUCTION ALONG DEMYELINATED AXONS BY ACTION-POTENTIAL-ENCODED SECOND HARMONIC GENERATION

Journal of Innovative Optical Health Sciences ◽

10.1142/s1793545813300036 ◽

2014 ◽

Vol 07 (01) ◽

pp. 1330003 ◽

Cited By ~ 2

Author(s):

ZHI-HUI LUO ◽

JIANG-XU CHEN ◽

YI-MEI HUANG ◽

HONG-QIN YANG ◽

JU-QIANG LIN ◽

...

Keyword(s):

Action Potential ◽

Second Harmonic Generation ◽

Harmonic Generation ◽

Refractory Period ◽

Action Potentials ◽

Demyelinating Disease ◽

Second Harmonic ◽

Temporal Distribution ◽

Demyelinating Diseases

Action-potential-encoded optical second harmonic generation (SHG) has been recently proposed for use in detecting the axonal damage in patients with demyelinating diseases. In this study, the characterization of signal conduction along axons of two different levels of demyelination was studied via a modified Hodgkin–Huxley model, because some types of demyelinating disease, i.e., primary progressive and secondary progressive multiple sclerosis, are difficult to be distinguished by magnetic resonance imaging (MRI), we focused on the differences in signal conduction between two different demyelinated axons, such as the first-level demyelination and the second-level demyelination. The spatio-temporal distribution of action potentials along demyelinated axons and conduction properties including the refractory period and frequency encoding in these two patterns were investigated. The results showed that demyelination could induce the decrease both in the amplitude of action potentials and the ability of frequency coding. Furthermore, the signal conduction velocity in the second-level demyelination was about 21% slower than that in the first-level demyelination. The refractory period in the second-level demyelination was about 32% longer than the first-level. Thus, detecting the signal conduction in demyelinated axons by action-potential-encoded optical SHG could greatly improve the assessment of demyelinating disorders to classify the patients. This technique also offers a potential fast and noninvasive optical approach for monitoring membrane potential.

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Reverse use dependence of calcium sensitizer levosimendan on action potential duration shortening prevents ventricular arrhythmia during therapeutic hypothermia

European Heart Journal ◽

10.1093/ehjci/ehaa946.3698 ◽

2020 ◽

Vol 41 (Supplement_2) ◽

Author(s):

Y.C Hsieh ◽

C.H Li ◽

J.C Lin ◽

C.J Weng ◽

Y.S Chien ◽

...

Keyword(s):

Ventricular Arrhythmia ◽

Action Potential ◽

Therapeutic Hypothermia ◽

Action Potential Duration ◽

Heart Failure Treatment ◽

Novel Approach ◽

Mapping System ◽

Diastolic Interval ◽

K Current ◽

Calcium Sensitizer

Abstract Background Therapeutic hypothermia (TH) increases the risk of ventricular arrhythmia (VA) by prolonging action potential duration (APD) and steepening the APD restitution (APDR). The calcium sensitizer levosimendan, a medication for heart failure treatment, has been reported to shorten APD by enhancing ATP-sensitive K current and affect the APDR. Purpose We hypothesized that levosimendan might shorten the already prolonged APD particularly at long pacing cycle length (PCL), thus decreases the maximal slope of APDR, and prevent VA during TH. Methods Langendorff-perfused isolated rabbit hearts were subjected to 15-min TH (30°C) followed by 30-min treatment with levosimendan (0.5 μM, n=9) or vehicle (n=8). Using an optical mapping system, APD was evaluated by S1 pacing and APDR curve was plotted using APD70 versus diastolic interval. Ventricular fibrillation (VF) inducibility was evaluated by burst pacing for 30 s at the shortest PCL that achieved 1:1 ventricular capture. Results The APD was shortened from 259±8 ms at TH to 241±18 ms after levosimendan infusion at long PCL of 400 ms (p=0.024). However, at short PCL of 280 ms, the APD was not changed before (194±19) and after (188±23) levosimendan during TH (p=0.61). Levosimendan decreases the maximal slope of APDR curve from 1.99±0.65 at TH to 1.41±0.32 after adding levosimendan (p=0.034). The VF inducibility was decreased by levosimendan from 39±30% at 30°C to 14±12% with levosimendan (p=0.023). In control hearts, the maximal slope of APDR (p=0.75) and VF inducibility (p=0.12) were not changed by vehicle during TH. Conclusion Levosimendan might protect the hearts against VA during TH by shortening APD at long PCL and flattening the APDR. Enhancing ATP-sensitive K current with levosimendan during TH might be a novel approach to prevent VA during TH. Funding Acknowledgement Type of funding source: None

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Electrophysiological characterization of single pregnant rat myometrial cells in short-term primary culture

AJP Cell Physiology ◽

10.1152/ajpcell.1986.250.1.c47 ◽

1986 ◽

Vol 250 (1) ◽

pp. C47-C54 ◽

Cited By ~ 76

Author(s):

P. Mollard ◽

J. Mironneau ◽

T. Amedee ◽

C. Mironneau

Keyword(s):

Action Potential ◽

Primary Culture ◽

Membrane Resistance ◽

Resting Potential ◽

Short Term ◽

Pregnant Rat ◽

Myometrial Cells ◽

The Mean ◽

Electrophysiological Characterization ◽

Specific Membrane

Smooth muscle cells were isolated from the longitudinal layer of pregnant rat myometrium (18-19 days) and studied either freshly dissociated or during short-term primary culture (until 30 h) using intracellular microelectrode techniques and direct microscopic observation. The isolated myometrial cells excluded trypan blue vital stain and could repetitively contract in response to various stimuli. Electrophysiological studies at 37 degrees C showed normal resting potential (-54.5 +/- 7.5 mV, n = 71). Action potentials with overshoot (+7.8 +/- 4.6 mV, n = 71) could be elicited by intracellular stimulation. Moreover, the membrane potential was largely dependent on the external K+ concentration. The action potential was suppressed in a Ca2+-free solution [with 0.1 mM ethyleneglycol-bis(beta-aminoethylether)-N,N'-tetraacetic acid], and the overshoot amplitude was clearly Ca2+ dependent. The action potential was inhibited by Mn2+ ions (1 mM), Co2+ ions (1 mM), and D 600 (1 microM) but was unaffected by tetrodotoxin (2 microM) and external Na+ removal. Tetraethylammonium chloride (TEA, 10 mM) and 4-aminopyridine (4-AP, 10 mM) increased both overshoot amplitude and duration of the electrical responses. When the cell surface area was measured with light microscopy, the mean specific membrane resistance was 14.8 +/- 4.6 k omega . cm2 (n = 14), and the mean specific membrane capacitance was 2.3 +/- 0.7 microF/cm2 (n = 14). Outward-going rectification was consistently observed in all cells examined. This was either inhibited by TEA and 4-AP (10 mM each) or reduced in the presence of 1 mM Mn2+.(ABSTRACT TRUNCATED AT 250 WORDS)

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Frequency- and voltage-dependent effects of disopyramide in canine Purkinje fibers

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y89-115 ◽

1989 ◽

Vol 67 (7) ◽

pp. 710-721 ◽

Cited By ~ 2

Author(s):

Matthew A. Flemming ◽

Betty I. Sasyniuk

Keyword(s):

Potassium Channels ◽

Action Potential ◽

Sodium Channel ◽

Action Potential Duration ◽

Refractory Period ◽

Drug Effect ◽

Effective Refractory Period ◽

Slow Inactivation ◽

Purkinje Fibers ◽

Rate Dependent

The voltage- and frequency-dependent blocking actions of disopyramide were assessed in canine Purkinje fibers within the framework of concentrations, membrane potentials, and heart rates which have relevance to the therapeutic actions of this drug. [Formula: see text] was used to assess the magnitude of sodium channel block. Disopyramide produced a concentration- and rate-dependent increase in the magnitude and kinetics of [Formula: see text] depression. Effects on activation time (used as an estimate of drug effect on conduction) were exactly analogous to effects on [Formula: see text]. A concentration-dependent increase in tonic block was also observed. Despite significant increases in tonic block at more depolarized potentials, rate-dependent block increased only marginally with membrane potential over the range of potentials in which propagated action potentials occur. Increases in extracellular potassium concentration accentuated drug effect on [Formula: see text] but attenuated drug effect on action potential duration. Recovery from rate-dependent block followed two exponential processes with time constants of 689 ± 535 ms and 15.7 ± 2.7 s. The latter component represents dissociation of drug from its binding site and the former probably represents recovery from slow inactivation. A concentration-dependent increase in the amplitude of the first component suggested that disopyramide may promote slow inactivation. There was less than 5% recovery from block during intervals equivalent to clinical diastole. Thus, depression of beats of all degrees of prematurity was similar to that of basic drive beats. Prolongation of action potential duration by therapeutic concentrations of drug following a long quiescent interval was minimal. However, profound lengthening of action potential duration occurred following washout of drug effect at a time when [Formula: see text] depression had reverted to normal, suggesting that binding of disopyramide to potassium channels may not be readily reversed. Variable effects on action potential duration may thus be attributed to a block of the window current flowing during the action potential being partially or over balanced by block of potassium channels. Purkinje fiber refractoriness was prolonged in a frequency-dependent manner. Disopyramide did not significantly alter the effective refractory period of basic beats but did increase the effective refractory period of sequential tightly coupled extra stimuli. The results can account for the antiarrhythmic actions of disopyramide during a rapid tachycardia and prevention of its initiation by programmed electrical stimulation.Key words: action potential duration, effective refractory period, upstroke velocity, conduction, rate of sodium channel unblocking.

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