scholarly journals Acacetin suppresses the electrocardiographic and arrhythmic manifestations of the J wave syndromes

PLoS ONE ◽  
2020 ◽  
Vol 15 (11) ◽  
pp. e0242747
Author(s):  
José M. Di Diego ◽  
Bence Patocskai ◽  
Hector Barajas-Martinez ◽  
Virág Borbáth ◽  
Michael J. Ackerman ◽  
...  
Keyword(s):  
Channel Blocker ◽  
Outward Current ◽  
Experimental Models ◽  
Transient Outward Current ◽  
Whole Cell Patch Clamp ◽  
Increased Risk ◽  
Life Threatening ◽  
Whole Heart ◽  
Unipolar Electrograms ◽  
J Wave

Background J wave syndromes (JWS), including Brugada (BrS) and early repolarization syndromes (ERS), are associated with increased risk for life-threatening ventricular arrhythmias. Pharmacologic approaches to therapy are currently very limited. Here, we evaluate the effects of the natural flavone acacetin. Methods The effects of acacetin on action potential (AP) morphology and transient outward current (Ito) were first studied in isolated canine RV epicardial myocytes using whole-cell patch clamp techniques. Acacetin’s effects on transmembrane APs, unipolar electrograms and transmural ECGs were then studied in isolated coronary-perfused canine RV and LV wedge preparations as well as in whole-heart, Langendorff-perfused preparations from which we recorded a 12 lead ECG and unipolar electrograms. Using floating glass microelectrodes we also recorded transmembrane APs from the RVOT of the whole-heart model. The Ito agonist NS5806, sodium channel blocker ajmaline, calcium channel blocker verapamil or hypothermia (32°C) were used to pharmacologically mimic the genetic defects and conditions associated with JWS, thus eliciting prominent J waves and provoking VT/VF. Results Acacetin (5–10 μM) reduced Ito density, AP notch and J wave area and totally suppressed the electrocardiographic and arrhythmic manifestation of both BrS and ERS, regardless of the experimental model used. In wedge and whole-heart models of JWS, increasing Ito with NS5806, decreasing INa or ICa (with ajmaline or verapamil) or hypothermia all resulted in accentuation of epicardial AP notch and ECG J waves, resulting in characteristic BrS and ERS phenotypes. Phase 2-reentrant extrasystoles originating from the RVOT triggered VT/VF. The J waves in leads V1 and V2 were never associated with a delay of RVOT activation and always coincided with the appearance of the AP notch recorded from RVOT epicardium. All repolarization defects giving rise to VT/VF in the BrS and ERS models were reversed by acacetin, resulting in total suppression of VT/VF. Conclusions We present experimental models of BrS and ERS capable of recapitulating all of the ECG and arrhythmic manifestations of the JWS. Our findings provide definitive support for the repolarization but not the depolarization hypothesis proposed to underlie BrS and point to acacetin as a promising new pharmacologic treatment for JWS.

I(to) and action potential notch are smaller in left vs. right canine ventricular epicardium

1996 ◽  
Vol 271 (2) ◽  
pp. H548-H561 ◽  
Author(s):  
J. M. Di Diego ◽  
Z. Q. Sun ◽  
C. Antzelevitch
Keyword(s):  
Action Potential ◽  
Phase 1 ◽  
Outward Current ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Pharmacological Agents ◽  
Whole Cell Patch Clamp ◽  
Chloride Channel Blocker ◽  
The Right ◽  
Basic Cycle Length

Transmural heterogeneities of repolarizing currents underlie prominent differences in the electrophysiology and pharmacology of ventricular epicardial, endocardial, and M cells in a number of species. The degree to which heterogeneities exist between the right and left ventricles is not well appreciated. The present study uses standard microelectrode and whole cell patch-clamp techniques to contrast the electrophysiological characteristics and pharmacological responsiveness of tissues and myocytes isolated from right (RVE) and left canine ventricular epicardium (LVE). RVE and LVE studied under nearly identical conditions displayed major differences in the early repolarizing phases of the action potential. The magnitude of phase 1 in RVE was nearly threefold that in LVE: 28.7 +/- 6.2 vs. 10.6 +/- 4.1 mV (basic cycle length = 2,000 ms). Phase 1 in RVE was also more sensitive to alterations of the stimulation rate and to 4-aminopyridine (4-AP), suggesting a much greater contribution of the transient outward current (I(to) 1) in RVE than in LVE. The combination of 4-AP plus ryanodine, low chloride, or 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (chloride channel blocker) completely eliminated the notch and all rate dependence of the early phases of the action potential, making RVE and LVE indistinguishable. At +70 mV, RVE myocytes displayed peak I(to) 1 densities between 28 and 37 pA/pF. LVE myocytes included cells with similar I(to) 1 densities (thought to represent subsurface cells) but also cells with much smaller current levels (thought to represent surface cells). Average peak I(to) 1 density was significantly smaller in LVE than in RVE at voltages more than or equal to +10 mV. Our data point to prominent differences in the magnitude of the I(to) 1-mediated action potential notch in cells at the surface of RVE compared with the LVE and suggest that important distinctions may exist in the response of these two tissues to pharmacological agents and pathophysiological states, as previously demonstrated for epicardium and endocardium. Our findings also suggest that a calcium-activated outward current contributes to the early repolarization phase in RVE and LVE and that the influence of this current, although small, is more important in the left ventricle.

Ca2+-activated Cl− current in cultured myenteric neurons from murine proximal colon

2003 ◽  
Vol 284 (4) ◽  
pp. C839-C847 ◽  
Author(s):  
Sok Han Kang ◽  
Pieter Vanden Berghe ◽  
Terence K. Smith
Keyword(s):  
Membrane Potential ◽  
Channel Blocker ◽  
Reversal Potential ◽  
Outward Current ◽  
Proximal Colon ◽  
Time Dependent ◽  
Equilibrium Potential ◽  
Resting Membrane Potential ◽  
Myenteric Neurons ◽  
Whole Cell Patch Clamp

Whole cell patch-clamp recordings were made from cultured myenteric neurons taken from murine proximal colon. The micropipette contained Cs+ to remove K+ currents. Depolarization elicited a slowly activating time-dependent outward current ( I tdo), whereas repolarization was followed by a slowly deactivating tail current ( I tail). I tdo and I tail were present in ∼70% of neurons. We identified these currents as Cl− currents ( I Cl), because changing the transmembrane Cl− gradient altered the measured reversal potential ( E rev) of both I tdo and I tail with that for I tailshifted close to the calculated Cl− equilibrium potential ( E Cl). I Cl are Ca2+-activated Cl− current [ I Cl(Ca)] because they were Ca2+dependent. E Cl, which was measured from the E rev of I Cl(Ca) using a gramicidin perforated patch, was −33 mV. This value is more positive than the resting membrane potential (−56.3 ± 2.7 mV), suggesting myenteric neurons accumulate intracellular Cl−. ω-Conotoxin GIVA [0.3 μM; N-type Ca2+ channel blocker] and niflumic acid [10 μM; known I Cl(Ca) blocker], decreased the I Cl(Ca). In conclusion, these neurons have I Cl(Ca) that are activated by Ca2+entry through N-type Ca2+ channels. These currents likely regulate postspike frequency adaptation.

Effects of thyroid hormone on action potential and repolarizing currents in rat ventricular myocytes

2000 ◽  
Vol 278 (2) ◽  
pp. E302-E307 ◽  
Author(s):  
Zhuo-Qian Sun ◽  
Kaie Ojamaa ◽  
William A. Coetzee ◽  
Michael Artman ◽  
Irwin Klein
Keyword(s):  
Action Potential ◽  
Cardiac Electrophysiology ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Mechanisms Of Action ◽  
Transient Outward Current ◽  
Prolonged Action ◽  
Electrophysiological Properties ◽  
Whole Cell Patch Clamp ◽  
Prolonged Action Potential Duration

Thyroid hormones play an important role in cardiac electrophysiology through both genomic and nongenomic mechanisms of action. The effects of triiodothyronine (T3) on the electrophysiological properties of ventricular myocytes isolated from euthyroid and hypothyroid rats were studied using whole cell patch clamp techniques. Hypothyroid ventricular myocytes showed significantly prolonged action potential duration (APD90) compared with euthyroid myocytes, APD90 of 151 ± 5 vs. 51 ± 8 ms, respectively. Treatment of hypothyroid ventricular myocytes with T3 (0.1 μM) for 5 min significantly shortened APD by 24% to 115 ± 10 ms. T3 similarly shortened APD in euthyroid ventricular myocytes, but only in the presence of 4-aminopyridine (4-AP), an inhibitor of the transient outward current ( I to), which prolonged the APD by threefold. Transient outward current ( I to) was not affected by the acute application of T3 to either euthyroid or hypothyroid myocytes; however, I to density was significantly reduced in hypothyroid compared with euthyroid ventricular myocytes.

Divalent cations modulate the transient outward current in rat ventricular myocytes

1991 ◽  
Vol 261 (2) ◽  
pp. C310-C318 ◽  
Author(s):  
Z. S. Agus ◽  
I. D. Dukes ◽  
M. Morad
Keyword(s):  
Hippocampal Neurons ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Divalent Cations ◽  
Outward Current ◽  
Transient Outward Current ◽  
Patch Clamp Technique ◽  
Rat Ventricular Myocytes ◽  
Specific Effects ◽  
Whole Cell Patch Clamp

The modulation of the transient outward K+ current (Ito) by divalent cations was studied in enzymatically isolated rat ventricular myocytes with the whole cell patch-clamp technique. At holding potentials negative to -70 mV, 1 mM Cd2+ suppressed Ito, whereas, at potentials positive to -50 mV, the current was augmented. These effects were caused by shifts in the voltage dependence of both activation and inactivation of Ito toward more positive potentials. Cd2+ also slowed the activation kinetics of Ito by shifting the voltage dependence of its rate of activation, but the rate of inactivation was unaffected. Other divalent cations produced similar shifts but at markedly different concentrations. Thus, in the millimolar range, a rightward shift of approximately 20 mV was produced by 3 Co2+, 5 Ni2+, and 10 Ca2+, whereas 10 microM concentrations of Cu2+ and Zn2+ produced equivalent shifts. Similar effects were seen in hippocampal neurons with micromolar concentrations of Zn2+. Thus divalent cations have marked and specific effects on the kinetics and voltage dependence of Ito and may serve as a regulatory mechanism in its activation, particularly in cells with resting potentials positive to -60 mV.

Properties of potassium currents in Purkinje cells of failing human hearts

2002 ◽  
Vol 283 (6) ◽  
pp. H2495-H2503 ◽  
Author(s):  
Wei Han ◽  
Liming Zhang ◽  
Gernot Schram ◽  
Stanley Nattel
Keyword(s):  
Purkinje Cells ◽  
Ventricular Myocytes ◽  
Outward Current ◽  
Ionic Currents ◽  
Time Dependent ◽  
Transient Outward Current ◽  
Whole Cell Patch Clamp ◽  
Cardiac Purkinje Fibers ◽  
Cardiac Purkinje Cells ◽  
Hyperpolarization Activated Current

Cardiac Purkinje fibers play an important role in cardiac arrhythmias, but no information is available about ionic currents in human cardiac Purkinje cells (PCs). PCs and midmyocardial ventricular myocytes (VMs) were isolated from explanted human hearts. K+ currents were evaluated at 37°C with whole cell patch clamp. PCs had clear inward rectifier K+current ( I K1), with a density not significantly different from VMs between −110 and −20 mV. A Cs+-sensitive, time-dependent hyperpolarization-activated current was measurable negative to −60 mV. Transient outward current ( I to) density was smaller, but end pulse sustained current ( I sus) was larger, in PCs vs. VMs. I to recovery was substantially slower in PCs, leading to strong frequency dependence. Unlike VM I to, which was unaffected by 10 mM tetraethylammonium, Purkinje I to was strongly inhibited by tetraethylammonium, and Purkinje I to was 10-fold more sensitive to 4-aminopyridine than VM. PC I sus was also reduced strongly by 10 mM tetraethylammonium. In conclusion, human PCs demonstrate a prominent I K1, a time-dependent hyperpolarization-activated current, and an I towith pharmacological sensitivity and recovery kinetics different from those in the atrium or ventricle and compatible with a different molecular basis.

Ca(2+)-dependent outward currents in myocytes from epicardial border zone of 5-day infarcted canine heart

1997 ◽  
Vol 273 (3) ◽  
pp. H1386-H1394 ◽  
Author(s):  
R. Aggarwal ◽  
J. Pu ◽  
P. A. Boyden
Keyword(s):  
Action Potentials ◽  
Time Course ◽  
Outward Current ◽  
Border Zone ◽  
Disulfonic Acid ◽  
Transient Outward Current ◽  
Canine Heart ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Transmembrane Action Potentials

Myocytes from the epicardial border zone (EBZ) of the 5-day infarcted canine heart (IZ) have abnormal transmembrane action potentials, reduced L-type Ca2+ currents (ICa,L) and altered intracellular Ca2+ (Cai) transients compared with those of normal epicardial myocytes (NZ). We hypothesized that altered Cai cycling might be reflected in differences in Cai-dependent outward currents (Ito2). We recorded Ito2 in NZ and IZ using whole cell patch-clamp techniques. Ito2 was defined as the amplitude of the 4-aminopyridine-resistant transient outward current that was blocked by 200 microM 4,4'-diisothiocyanostilbene-2,2'-disulfonic acid (DIDS) or DIDS+ ryanodine (2 microM). Ito2 were present in both NZ and IZ, but peak density was significantly reduced in IZ, particularly at positive plateau voltages. Time course of decay of Ito2 was biexponential and similar in NZ and IZ. A given peak ICa,L was usually associated with a smaller peak Ito2 in IZ. These differences were exaggerated when Ito2 and Cai transients were determined in rapidly paced cells. In summary, myocytes surviving in the EBZ of the infarcted heart have Ito2, yet they are reduced in density and can vary, particularly at fast pacing rates.

Comparative mechanisms of 4-aminopyridine-resistant Ito in human and rabbit atrial myocytes

1995 ◽  
Vol 269 (2) ◽  
pp. H463-H472 ◽  
Author(s):  
G. R. Li ◽  
J. Feng ◽  
Z. Wang ◽  
B. Fermini ◽  
S. Nattel
Keyword(s):  
Outward Current ◽  
Pulse Frequency ◽  
Transient Outward Current ◽  
Tetraacetic Acid ◽  
Atrial Myocytes ◽  
Human Atrial Myocytes ◽  
Atrial Cells ◽  
Whole Cell Patch Clamp ◽  
Current Voltage ◽  
Rabbit Atrium

The cardiac transient outward current (Ito) has been shown in several species to consist of two components: 1) a 4-aminopyridine (4-AP)-sensitive component (Ito1) and 2) a 4-AP-resistant component (Ito2). In rabbits, Ito2 is a Ca(2+)-dependent Cl- current [ICl(Ca)]; similar mechanisms have been suggested to underlie Ito2 in human atrium. We used whole cell patch-clamp techniques to define the mechanism of Ito2 (defined as the component resistant to 5 mM 4-AP) in human atrial myocytes, with parallel experiments performed in rabbit atrial cells. In rabbit atrium, Ito2 activated more slowly than Ito1 and had a bell-shaped current-voltage of Ito with properties similar to Ito2 in the rabbit, and a similar component recorded with pipette K+ replaced by Cs+ was suppressed by the substitution of methanesulfonate for Cl- in the superfusate. In human cells, a 4-AP-resistant Ito2 was recorded at a depolarizing pulse frequency of 1 Hz, but not at 0.1 Hz. Ito2 activated rapidly and inactivated earlier than Ito1, whereas its I-V relation was linear like that of Ito1. Ryanodine had no effect on human atrial Ito. When K(+)-free pipette solutions were used, no Ito was recorded in 30 human atrial myocytes, and external Cl- replacement with methanesulfonate failed to reveal an Ito. In 13 human myocytes, isoproterenol increased ICa but failed to activate an Ito compatible with ICl(Ca). Whereas caffeine suppressed human atrial Ito, it also suppressed Ito1 [in the presence of 200 microM Cd2+ to block ICa and 5 mM intracellular ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid to buffer intracellular Ca2+] in both human and rabbit atrium, indicating an action unrelated to Ca(2+)-triggered Ca2+ release. In conclusion, we were unable to demonstrate the presence of ICl(Ca) in human atrial myocytes, and the 4-AP-resistant component of Ito appeared to be due to 4-AP unblocking.

Comparison of Ito in young and adult human atrial myocytes: evidence for developmental changes

1995 ◽  
Vol 268 (3) ◽  
pp. H1335-H1342 ◽  
Author(s):  
W. J. Crumb ◽  
J. D. Pigott ◽  
C. W. Clarkson
Keyword(s):  
Current Density ◽  
Outward Current ◽  
Inward Rectifier ◽  
Developmental Changes ◽  
Transient Outward Current ◽  
Atrial Myocytes ◽  
Patch Clamp Technique ◽  
Whole Cell Patch Clamp ◽  
Age Related ◽  
Age Related Changes

In an effort to understand the ionic basis for the developmental changes that have been reported to occur in the configuration of the human atrial action potential, we characterized the transient outward current (Ito) and the inward rectifier current in atrial myocytes isolated from 20 young (ages 1 day-2.5 yr) and 8 adult (11–68 yr) human hearts using the whole cell patch-clamp technique. We found evidence for statistically significant (P < 0.05) age-related changes in the Ito, including 1) the presence of an Ito in only 67% of the cells isolated from young hearts vs. 100% of the cells isolated from adult hearts, 2) an almost twofold increase in the current density of Ito in adult cells vs. young cells, and 3) recovery kinetics that are approximately twofold slower in young myocytes relative to adult myocytes. In contrast, there were no age-related changes found in the current density of the inward rectifier current or the sustained current measured after the decay of Ito. These results suggest important current-dependent changes that occur with age in human atria.

Postnatal rat nigrostriatal dopaminergic neurons exhibit five types of potassium conductances

1990 ◽  
Vol 64 (1) ◽  
pp. 262-272 ◽  
Author(s):  
N. L. Silva ◽  
C. M. Pechura ◽  
J. L. Barker
Keyword(s):  
Action Potential ◽  
Outward Current ◽  
Transient Outward Current ◽  
Channel Blockers ◽  
Current Response ◽  
Whole Cell Patch Clamp ◽  
Outward Currents ◽  
Potassium Conductances ◽  
Steady State Inactivation ◽  
Sustained Outward Current

1. We have investigated the electrical properties of neurons acutely dissociated from the substantia nigra zona compacta (SNZC) of the postnatal rat with whole cell patch-clamp recordings. Retrogradely labeled nigrostriatal neurons were identified with the use of rhodamine-labeled fluorescent latex microspheres. Over 90% of the rhodamine-labeled neurons in the SNZC demonstrated formaldehyde/glutaraldehyde-induced catecholamine fluorescence, indicating that they were dopaminergic (DA) neurons. 2. DA neurons had 15-20 microns ovoid or fusiform-shaped cell bodies with 2-3 thick proximal processes. Labeled neurons generated spontaneous action-potential activity in both regular and irregular patterns. These cells exhibited input resistances of 300-600 M omega and action-potential amplitudes of 60-80 mV. Locally applied dopamine inhibited the spontaneous activity of these neurons by hyperpolarizing the cells. 3. Outward currents were examined with voltage-clamp recordings using a tetrodotoxin (TTX)-containing medium. In all DA cells, depolarizing voltage commands activated several components of outward current depending on the holding potential of the cell. When cells were held at -40 mV (or more positive), voltage steps activated a sustained outward current. If the membrane potential was held more negative than -50 mV, a rapidly activating and inactivating component of outward current response could also be detected. 4. From a hyperpolarized holding potential (-90 mV) the transient outward current activated with depolarizing commands to -55 mV, peaking within 5 ms. The current inactivated with a monoexponential time constant of 53 +/- 4 (SE) ms. At more positive holding potentials (-40 mV) the steady-state inactivation of the current could be removed by applying a conditioning hyperpolarizing prepulse. In response to a fixed depolarizing voltage step, half-maximal inactivation occurred at about -65 mV. The transient current was blocked by 4-aminopyridine (4-AP). 5. The sustained outward currents were isolated by holding the cells at -40 mV. Two components of sustained outward current were distinguished by their sensitivity to the calcium channel blockers Co2+ (5 mM) and/or Cd2+ (200 microM). The current remaining in the presence of Co2+/Cd2+ was activated by depolarizing voltage commands more positive than -40 mV.(ABSTRACT TRUNCATED AT 400 WORDS)

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