Connexin43 silencing in myofibroblasts prevents arrhythmias in myocardial cultures: role of maximal diastolic potential

Type 2 long QT (LQT2) syndrome is a cardiac disorder associated with hERG channel mutation that may lead to tachyarrhythmia and sudden death. We developed a syncytial model of cardiomyocytes (CMs) differentiated from iPS cells derived from an LQT2 patient harboring an A422T mutation. The A422T mutation has been shown to cause a marked decrease in IKr current mainly due to a trafficking defect in the hERG channel. Immunostaining of cTnI revealed that CMs were isotropically distributed with well-formed sarcomeres. Both wild type (WT) and LQT2 monolayers were stable in culture for at least 60 days with spontaneous activity, and could be paced at cycle lengths (CL) from 2000 down to 300 ms. After staining the monolayers with di-4-ANEPPS, optical mapping showed that all monolayers formed a functional syncytium that supported propagating action potentials. LQT2 monolayers had longer APD80s than WT monolayers (332±43 ms, n=6, vs. 267±46 ms, n=18, mean±SD, CL = 700 ms, p<0.005), showing the delayed repolarization expected of the LQT2 phenotype. Reentrant spiral waves were observed in LQT2 (n=2), but not WT monolayers. Application of 0.2μM E-4031 (IKr blocker) slowed repolarization and prolonged APD80 in both WT and LQT2 monolayers, and slowed conduction velocity in WT monolayers (4.7±1.0 cm/s, n=6 vs. 10.4±1.4 cm/s, n=11 control, CL = 1000 ms). The slowing effect may reflect a role of IKr in setting the maximum diastolic potential in these CMs where IK1 is weakly expressed, as has been recently suggested. Application of 10μM ML-T531 (IKr activator) shortened APD80 in LQT2 monolayers (313±36 ms vs. 162±19 ms, n=4, p<0.0001), showing successful reversal of the LQT phenotype. ML-T531 also shortened APD80 in WT monolayers (202±43 ms vs. 154±26 ms, n=4, p<0.04). These results indicate that syncytial models of heritable cardiac disease are feasible and may be useful for studying drug effects that affect electrophysiology and arrhythmogenesis.

Download Full-text

The Major Role of IK1 in Mechanisms of Rotor Drift in the Atria: A Computational Study

Clinical Medicine Insights Cardiology ◽

10.4137/cmc.s39773 ◽

2016 ◽

Vol 10s1 ◽

pp. CMC.S39773 ◽

Cited By ~ 3

Author(s):

Omer Berenfeld

Keyword(s):

Atrial Fibrillation ◽

Complex Dynamics ◽

Computational Study ◽

Pulmonary Veins ◽

Heterogeneous Distribution ◽

Spatial Gradients ◽

Transmembrane Currents ◽

Drift Direction ◽

Diastolic Potential

Maintenance of paroxysmal atrial fibrillation (AF) by fast rotors in the left atrium (LA) or at the pulmonary veins (PVs) is not fully understood. This review describes the role of the heterogeneous distribution of transmembrane currents in the PVs and LA junction (PV-LAJ) in the localization of rotors in the PVs. Experimentally observed heterogeneities in IK1, IKs, IKr, Ito, and ICaL in the PV-LAJ were incorporated into models of human atrial kinetics to simulate various conditions and investigate rotor drifting mechanisms. Spatial gradients in the currents resulted in shorter action potential duration, less negative minimum diastolic potential, slower upstroke and conduction velocity for rotors in the PV region than in the LA. Rotors under such conditions drifted toward the PV and stabilized at the less excitable region. Our simulations suggest that IK1 heterogeneity is dominant in determining the drift direction through its impact on the excitability gradient. These results provide a novel framework for understanding the complex dynamics of rotors in AF.

Download Full-text

Role of IK and If in the pacemaker mechanisms of sino-atrial node myocytes

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y01-085 ◽

2001 ◽

Vol 79 (12) ◽

pp. 963-976 ◽

Cited By ~ 7

Author(s):

Hengtao Zhang ◽

Mario Vassalle

Keyword(s):

Delayed Rectifier ◽

Potential Range ◽

Patch Clamp Technique ◽

Time Intervals ◽

Delayed Rectifier Current ◽

Hyperpolarization Activated Current ◽

Short Time ◽

Perforated Patch Clamp ◽

Diastolic Potential

The role of IK (delayed rectifier current) and If (hyperpolarization-activated current) in dominant and subsidiary pacemaker ranges was studied in single myocytes isolated from the guinea pig sino-atrial node by means of a perforated patch-clamp technique. In the dominant pacemaker range (approx. 55 to 40 mV), IK tails are present whereas If is not activated. In the subsidiary pacemaker range (approx. 80 to 70 mV), If is large whereas IK is minimal and reversing. The threshold for If activation is more negative at short time intervals. Larger or longer depolarizations to 40 mV and +20 mV deactivate If more and are followed by faster reactivation of If. Steps of 200300 ms duration to +20 mV completely deactivate If. The slope conductance decreases during depolarizations at 40 and +20 mV and quickly re-increases after the steps. The If deactivation range is between 70 and +10 mV, with a V1/2 of 35 mV. Depolarizations from 80 to +20 mV at a rate of 120/min limit the subsequent If reactivation owing to the short diastole. We conclude that IK plays a predominant role in the dominant pacemaker range and If does so in the subsidiary pacemaker range. Either pacemaker mechanism is used by sino-atrial node cells depending on the diastolic potential range. A previous depolarization markedly increases the amplitude and rate of If reactivation.Key words: dominant and subsidiary pacemaker ranges, sinus discharge and dual pacemaker mechanisms, delayed rectifier current IK, hyperpolarization-activated current If, factors regulating If, pacemaker shifts.

Download Full-text

Inhibition of rat ventricularI K1 with antisense oligonucleotides targeted to Kir2.1 mRNA

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1998.274.3.h892 ◽

1998 ◽

Vol 274 (3) ◽

pp. H892-H900 ◽

Cited By ~ 9

Author(s):

Tomoe Y. Nakamura ◽

Michael Artman ◽

Bernardo Rudy ◽

William A. Coetzee

Keyword(s):

Antisense Oligonucleotides ◽

Essential Role ◽

Xenopus Oocytes ◽

Ventricular Myocytes ◽

Multiple Channel ◽

Medium Specificity ◽

Current Cell ◽

Diastolic Potential ◽

Kir2.1 Channel

The cardiac inward rectifying K+ current ( I K1) is important in maintaining the maximum diastolic potential. We used antisense oligonucleotides to determine the role of Kir2.1 channel proteins in the genesis of native rat ventricular I K1. A combination of two antisense phosphorothioate oligonucleotides inhibited heterologously expressed Kir2.1 currents in Xenopus oocytes, either when coinjected with Kir2.1 cRNA or when applied in the incubation medium. Specificity was demonstrated by the lack of inhibition of Kir2.2 and Kir2.3 currents in oocytes. In rat ventricular myocytes (4–5 days culture), these oligonucleotides caused a significant reduction of whole cell I K1(without reducing the transient outward K+ current or the L-type Ca2+ current). Cell-attached patches demonstrated the occurrence of multiple channel events in control myocytes (8, 14, 21, 35, 43, and 80 pS). The 21-pS channel was specifically knocked down in antisense-treated myocytes (fewer patches contained this channel, and its open frequency was reduced). These results demonstrate that the Kir2.1 gene encodes a specific native 21-pS K+-channel protein and that this channel has an essential role in the genesis of cardiac I K1.

Download Full-text

Effect of tetraethylammonium chloride on action potential in cardiac Purkinje fibers

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1981.241.2.h139 ◽

1981 ◽

Vol 241 (2) ◽

pp. H139-H144

Author(s):

S. Ito ◽

B. Surawicz

Keyword(s):

Action Potential ◽

Outward Current ◽

Extracellular Potassium ◽

Tetraethylammonium Chloride ◽

Purkinje Fibers ◽

Extracellular Potassium Concentration ◽

Cardiac Purkinje Fibers ◽

Prolonged Action Potential Duration ◽

Diastolic Potential

Intracellular loading with 20 mM tetraethylammonium chloride (TEA) diffusing through the cut end of the preparations prolonged action potential duration (APD) in dog Purkinje fibers without changing maximum diastolic potential, overshoot, and dV/dtmax. The APD was prolonged at all rates of stimulation, but, contrary to the normal rules, APD increased more after longer than after shorter interstimulus intervals. TEA increased the number of beats required to achieve the new steady-state APD after an abrupt change in the rate of stimulation. The effect of varying extracellular potassium concentration on maximal diastolic potential suggested that intracellular loading with TEA had no effect on the time-independent "background" outward current (IK1). If we ascribe all observed TEA effects to the reduction of time dependent slow outward current Ix1, we can propose a hypothesis concerning the role of Ix1 in the regulation of APD at slow heart rates.

Download Full-text

Role of dactinomycin in the improved survival of children with Wilms' tumor

JAMA ◽

10.1001/jama.195.12.1005 ◽

1966 ◽

Vol 195 (12) ◽

pp. 1005-1009 ◽

Cited By ~ 18

Author(s):

D. J. Fernbach

Keyword(s):

Wilms Tumor

Download Full-text

Role of the allergist in diagnosis and management of patients with uveitis

JAMA ◽

10.1001/jama.195.3.167 ◽

1966 ◽

Vol 195 (3) ◽

pp. 167-172 ◽

Cited By ~ 2

Author(s):

T. E. Van Metre

Keyword(s):

Diagnosis And Management

Download Full-text

The power of norms to sway fused group members

Behavioral and Brain Sciences ◽

10.1017/s0140525x18001644 ◽

2018 ◽

Vol 41 ◽

Cited By ~ 1

Author(s):

Winnifred R. Louis ◽

Craig McGarty ◽

Emma F. Thomas ◽

Catherine E. Amiot ◽

Fathali M. Moghaddam

Keyword(s):

Evolutionary Anthropology ◽

Normative Systems ◽

Violent Extremism ◽

Identity Fusion ◽

Group Members

AbstractWhitehouse adapts insights from evolutionary anthropology to interpret extreme self-sacrifice through the concept of identity fusion. The model neglects the role of normative systems in shaping behaviors, especially in relation to violent extremism. In peaceful groups, increasing fusion will actually decrease extremism. Groups collectively appraise threats and opportunities, actively debate action options, and rarely choose violence toward self or others.

Download Full-text

Elaborating the role of reflection and individual differences in the study of folk-economic beliefs

Behavioral and Brain Sciences ◽

10.1017/s0140525x18000274 ◽

2018 ◽

Vol 41 ◽

Author(s):

Kevin Arceneaux

Keyword(s):

Decision Making ◽

Individual Differences ◽

Cognitive Processes ◽

Evolutionary History ◽

Behavioral Responses ◽

History Of ◽

Economic Beliefs

AbstractIntuitions guide decision-making, and looking to the evolutionary history of humans illuminates why some behavioral responses are more intuitive than others. Yet a place remains for cognitive processes to second-guess intuitive responses – that is, to be reflective – and individual differences abound in automatic, intuitive processing as well.

Download Full-text

The role of affect in feelings of obligation

Behavioral and Brain Sciences ◽

10.1017/s0140525x19002449 ◽

2020 ◽

Vol 43 ◽

Author(s):

Stefen Beeler-Duden ◽

Meltem Yucel ◽

Amrisha Vaish

Keyword(s):

Positive Emotions ◽

The Creation ◽

Sense Of Obligation

Abstract Tomasello offers a compelling account of the emergence of humans’ sense of obligation. We suggest that more needs to be said about the role of affect in the creation of obligations. We also argue that positive emotions such as gratitude evolved to encourage individuals to fulfill cooperative obligations without the negative quality that Tomasello proposes is inherent in obligations.

Download Full-text