scholarly journals Suppression of ventricular arrhythmias by targeting late L-type Ca2+ current

2021 ◽  
Vol 153 (12) ◽  
Author(s):  
Marina Angelini ◽  
Arash Pezhouman ◽  
Nicoletta Savalli ◽  
Marvin G. Chang ◽  
Federica Steccanella ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Ventricular Arrhythmias ◽  
Ventricular Myocytes ◽  
Ex Vivo ◽  
Selective Reduction ◽  
Antiarrhythmic Action ◽  
Early Afterdepolarizations ◽  
Rat Hearts ◽  
New Strategy ◽  
Early Peak

Ventricular arrhythmias, a leading cause of sudden cardiac death, can be triggered by cardiomyocyte early afterdepolarizations (EADs). EADs can result from an abnormal late activation of L-type Ca2+ channels (LTCCs). Current LTCC blockers (class IV antiarrhythmics), while effective at suppressing EADs, block both early and late components of ICa,L, compromising inotropy. However, computational studies have recently demonstrated that selective reduction of late ICa,L (Ca2+ influx during late phases of the action potential) is sufficient to potently suppress EADs, suggesting that effective antiarrhythmic action can be achieved without blocking the early peak ICa,L, which is essential for proper excitation–contraction coupling. We tested this new strategy using a purine analogue, roscovitine, which reduces late ICa,L with minimal effect on peak current. Scaling our investigation from a human CaV1.2 channel clone to rabbit ventricular myocytes and rat and rabbit perfused hearts, we demonstrate that (1) roscovitine selectively reduces ICa,L noninactivating component in a human CaV1.2 channel clone and in ventricular myocytes native current, (2) the pharmacological reduction of late ICa,L suppresses EADs and EATs (early after Ca2+ transients) induced by oxidative stress and hypokalemia in isolated myocytes, largely preserving cell shortening and normal Ca2+ transient, and (3) late ICa,L reduction prevents/suppresses ventricular tachycardia/fibrillation in ex vivo rabbit and rat hearts subjected to hypokalemia and/or oxidative stress. These results support the value of an antiarrhythmic strategy based on the selective reduction of late ICa,L to suppress EAD-mediated arrhythmias. Antiarrhythmic therapies based on this idea would modify the gating properties of CaV1.2 channels rather than blocking their pore, largely preserving contractility.

Increasing I Ks corrects abnormal repolarization in rabbit models of acquired LQT2 and ventricular hypertrophy

2002 ◽  
Vol 283 (2) ◽  
pp. H664-H670 ◽  
Author(s):  
Xiaoping Xu ◽  
Joseph J. Salata ◽  
Jixin Wang ◽  
Ying Wu ◽  
Gan-Xin Yan ◽  
...  
Keyword(s):  
Ventricular Arrhythmias ◽  
Ventricular Hypertrophy ◽  
Voltage Dependence ◽  
Ventricular Myocytes ◽  
Delayed Rectifier ◽  
Long Qt ◽  
Early Afterdepolarizations ◽  
New Strategy ◽  
Rabbit Ventricular Myocytes ◽  
Qt Syndrome

Excessive action potential (AP) prolongation and early afterdepolarizations (EAD) are triggers of malignant ventricular arrhythmias. A slowly activating delayed rectifier K+ current ( I Ks) is important for repolarization of ventricular AP. We examined the effects of I Ks activation by a new benzodiazepine (L3) on the AP of control, dofetilide-treated, and hypertrophied rabbit ventricular myocytes. In both control and hypertrophied myocytes, L3 activated I Ks via a negative shift in the voltage dependence of activation and a slowing of deactivation. L3 had no effect on L-type Ca2+ current or other cardiac K+ currents tested. L3 shortened AP of control, dofetilide-treated, and hypertrophied myocytes more at 0.5 than 2 Hz. Selective activation of I Ks by L3 attenuates prolonged AP and eliminated EAD induced by rapidly activating delayed rectifier K+ current inhibition in control myocytes at 0.5 Hz and spontaneous EAD in hypertrophied myocytes at 0.2 Hz. Pharmacological activation of I Ks is a promising new strategy to suppress arrhythmias resulting from excessive AP prolongation in patients with certain forms of long QT syndrome or cardiac hypertrophy and failure.

scholarly journals Detecting Validated Intracellular ROS Generation with 18F-dihydroethidine-Based PET

2021 ◽  
Author(s):  
Edward C. T. Waters ◽  
Friedrich Baark ◽  
Zilin Yu ◽  
Filipa Mota ◽  
Thomas R. Eykyn ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Contractile Function ◽  
Ex Vivo ◽  
Glutathione Depletion ◽  
Ros Generation ◽  
Cardiac Contractile ◽  
Rat Hearts ◽  
Intracellular Ros ◽  
Cardiac Contractile Dysfunction

Abstract Purpose To determine the sensitivity of the 18F-radiolabelled dihydroethidine analogue ([18F]DHE) to ROS in a validated ex vivo model of tissue oxidative stress. Procedures The sensitivity of [18F]DHE to various ROS-generating systems was first established in vitro. Then, isolated rat hearts were perfused under constant flow, with contractile function monitored by intraventricular balloon. Cardiac uptake of infused [18F]DHE (50–150 kBq.min−1) was monitored by γ-detection, while ROS generation was invoked by menadione infusion (0, 10, or 50 μm), validated by parallel measures of cardiac oxidative stress. Results [18F]DHE was most sensitive to oxidation by superoxide and hydroxyl radicals. Normalised [18F]DHE uptake was significantly greater in menadione-treated hearts (1.44 ± 0.27) versus control (0.81 ± 0.07) (p < 0.05, n = 4/group), associated with concomitant cardiac contractile dysfunction, glutathione depletion, and PKG1α dimerisation. Conclusion [18F]DHE reports on ROS in a validated model of oxidative stress where perfusion (and tracer delivery) is unlikely to impact its pharmacokinetics.

Abstract 3503: Hydrogen Peroxide-Induced Afterdepolarizations are Dependent on Calmodulin Kinase II Signaling

Circulation ◽  
2008 ◽  
Vol 118 (suppl_18) ◽  
Author(s):  
Lai-Hua Xie ◽  
Fuhua Chen ◽  
James N Weiss
Keyword(s):  
Oxidative Stress ◽  
Hydrogen Peroxide ◽  
Ventricular Myocytes ◽  
Heart Association ◽  
Early Afterdepolarizations ◽  
Calmodulin Kinase ◽  
Repolarization Reserve ◽  
Delayed Afterdepolarizations ◽  
Rabbit Ventricular Myocytes ◽  
Camkii Activation

Background: In the heart, hydrogen peroxide (H 2 O 2 ) has been shown to cause early afterdepolarizations (EADs) and triggered activity by impairing Na current (I Na ) inactivation. Since H 2 O 2 has been recently shown to activate Ca 2+ /calmodulin kinase II (CaMKII), and since CaMKII activation has also been reported to impair I Na inactivation and predispose to EADs, we hypothesized that CaMKII activation by H 2 O 2 may be an important factor in the genesis of EADs induced by oxidative stress. Methods and Results: Patch-clamped Fluo-4 AM-loaded rabbit ventricular myocytes were exposed to H 2 O 2 (0.1–1mM), which induced spontaneous EADs after 5–15 min. Both the I Na blocker tetrodoxtin (TTX, 10 μM) and the I Ca,L blocker nifedipine shortened AP duration (APD) and suppressed EADs. H 2 O 2 increased both peak and steady-state I Ca,L under square-pulse voltage clamp, and enhanced I Ca,L to a greater extent during the AP plateau than during the AP upstroke under AP clamp conditions. In addition, by prolonging the AP plateau and increasing Ca influx via maintained I Ca,L , H 2 O 2 -induced EADs frequently caused DADs delayed afterdepolarizations (DADs) due to spontaneous SR Ca release waves after repolarization. KN-93(1 μM), a CaMKII inhibitor, prevented H 2 O 2 -induced EADs (n=4), whereas the inactive analogue KN-92 did not (n=5). Conclusion: These findings indicate that H 2 O 2 -induced EADs depend on both impaired I Na inactivation to reduce repolarization reserve and enhanced I Ca,L to reverse repolarization. Intact CaMKII signaling is necessary for EAD generation in this setting, presumably via its actions on I Na and I Ca,L , although direct redox effects on other ion channels/transporters may also be important. Our observations support a link between increased oxidative stress, CaMKII activation and afterdepolarizations as triggers of lethal ventricular arrhythmias in diseased heart. This research has received full or partial funding support from the American Heart Association, AHA National Center.

Glutathione and K+ channel remodeling in postinfarction rat heart

2002 ◽  
Vol 282 (6) ◽  
pp. H2346-H2355 ◽  
Author(s):  
George J. Rozanski ◽  
Zhi Xu
Keyword(s):  
Oxidative Stress ◽  
Glutathione Reductase ◽  
Ventricular Myocytes ◽  
K Channel ◽  
Glycolytic Flux ◽  
Cell Functions ◽  
Tissue Extracts ◽  
Rat Hearts ◽  
Glutamylcysteine Synthetase ◽  
Pentose Pathway

Electrical remodeling of the diseased ventricle is characterized by downregulation of K+ channels that control action potential repolarization. Recent studies suggest that this shift in electrophysiological phenotype involves oxidative stress and changes in intracellular glutathione (GSH), a key regulator of redox-sensitive cell functions. This study examined the role of GSH in regulating K+ currents in ventricular myocytes from rat hearts 8 wk after myocardial infarction (MI). Colorimetric analysis of tissue extracts showed that endogenous GSH levels were significantly less in post-MI hearts compared with controls, which is indicative of oxidative stress. This change in GSH status correlated with significant decreases in activities of glutathione reductase and γ-glutamylcysteine synthetase. Voltage-clamp studies of isolated myocytes from post-MI hearts demonstrated that downregulation of the transient outward K+ current ( I to) could be reversed by pretreatment with exogenous GSH or N-acetylcysteine, a precursor of GSH. Upregulation of I to was also elicited by dichloroacetate, which increases glycolytic flux through the GSH-related pentose pathway. This metabolic effect was blocked by inhibitors of glutathione reductase and the pentose pathway. These data indicate that oxidative stress-induced alteration in the GSH redox state plays an important role in I to channel remodeling and that GSH homeostasis is influenced by pathways of glucose metabolism.

scholarly journals Adeno-Associated Viral Transfer of Glyoxalase-1 Blunts Carbonyl and Oxidative Stresses in Hearts of Type 1 Diabetic Rats

Antioxidants ◽  
2020 ◽  
Vol 9 (7) ◽  
pp. 592
Author(s):  
Fadhel A. Alomar ◽  
Abdullah Al-Rubaish ◽  
Fahad Al-Muhanna ◽  
Amein K. Al-Ali ◽  
JoEllyn McMillan ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Ventricular Myocytes ◽  
Diabetic Rats ◽  
Confocal Imaging ◽  
Glyoxalase 1 ◽  
Microvascular Leakage ◽  
Oxidative Stresses ◽  
Rat Hearts ◽  
Longitudinal Strains

Accumulation of methylglyoxal (MG) arising from downregulation of its primary degrading enzyme glyoxalase-1 (Glo1) is an underlying cause of diabetic cardiomyopathy (DC). This study investigated if expressing Glo1 in rat hearts shortly after the onset of Type 1 diabetes mellitus (T1DM) would blunt the development of DC employing the streptozotocin-induced T1DM rat model, an adeno-associated virus containing Glo1 driven by the endothelin-1 promoter (AAV2/9-Endo-Glo1), echocardiography, video edge, confocal imaging, and biochemical/histopathological assays. After eight weeks of T1DM, rats developed DC characterized by a decreased E:A ratio, fractional shortening, and ejection fraction, and increased isovolumetric relaxation time, E: e’ ratio, and circumferential and longitudinal strains. Evoked Ca2+ transients and contractile kinetics were also impaired in ventricular myocytes. Hearts from eight weeks T1DM rats had lower Glo1 and GSH levels, elevated carbonyl/oxidative stress, microvascular leakage, inflammation, and fibrosis. A single injection of AAV2/9 Endo-Glo1 (1.7 × 1012 viron particles/kg) one week after onset of T1DM, potentiated GSH, and blunted MG accumulation, carbonyl/oxidative stress, microvascular leakage, inflammation, fibrosis, and impairments in cardiac and myocyte functions that develop after eight weeks of T1DM. These new data indicate that preventing Glo1 downregulation by administering AAV2/9-Endo-Glo1 to rats one week after the onset of T1DM, blunted the DC that develops after eight weeks of diabetes by attenuating carbonyl/oxidative stresses, microvascular leakage, inflammation, and fibrosis.

scholarly journals Increased susceptibility of aged hearts to ventricular fibrillation during oxidative stress

2009 ◽  
Vol 297 (5) ◽  
pp. H1594-H1605 ◽  
Author(s):  
Norishige Morita ◽  
Ali A. Sovari ◽  
Yuanfang Xie ◽  
Michael C. Fishbein ◽  
William J. Mandel ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Young Adult ◽  
Ventricular Myocytes ◽  
Tissue Level ◽  
Left Ventricular ◽  
Middle Aged ◽  
Aged Rat ◽  
Adult Rat ◽  
Inactive Form ◽  
Rat Hearts

Oxidative stress with hydrogen peroxide (H2O2) readily promotes early afterdepolarizations (EADs) and triggered activity (TA) in isolated rat and rabbit ventricular myocytes. Here we examined the effects of H2O2 on arrhythmias in intact Langendorff rat and rabbit hearts using dual-membrane voltage and intracellular calcium optical mapping and glass microelectrode recordings. Young adult rat (3–5 mo, N = 25) and rabbit (3–5 mo, N = 6) hearts exhibited no arrhythmias when perfused with H2O2 (0.1–2 mM) for up to 3 h. However, in 33 out of 35 (94%) aged (24–26 mo) rat hearts, 0.1 mM H2O2 caused EAD-mediated TA, leading to ventricular tachycardia (VT) and fibrillation (VF). Aged rabbits (life span, 8–12 yr) were not available, but 4 of 10 middle-aged rabbits (3–5 yr) developed EADs, TA, VT, and VF. These arrhythmias were suppressed by the reducing agent N-acetylcysteine (2 mM) and CaMKII inhibitor KN-93 (1 μM) but not by its inactive form (KN-92, 1 μM). There were no significant differences between action potential duration (APD) or APD restitution slope before or after H2O2 in aged or young adult rat hearts. In histological sections, however, trichrome staining revealed that aged rat hearts exhibited extensive fibrosis, ranging from 10–90%; middle-aged rabbit hearts had less fibrosis (5–35%), whereas young adult rat and rabbit hearts had <4% fibrosis. In aged rat hearts, EADs and TA arose most frequently (70%) from the left ventricular base where fibrosis was intermediate (∼30%). Computer simulations in two-dimensional tissue incorporating variable degrees of fibrosis showed that intermediate (but not mild or severe) fibrosis promoted EADs and TA. We conclude that in aged ventricles exposed to oxidative stress, fibrosis facilitates the ability of cellular EADs to emerge and generate TA, VT, and VF at the tissue level.

scholarly journals Stretch-activated channel activation promotes early afterdepolarizations in rat ventricular myocytes under oxidative stress

2009 ◽  
Vol 296 (5) ◽  
pp. H1227-H1235 ◽  
Author(s):  
Yanggan Wang ◽  
Ronald W. Joyner ◽  
Mary B. Wagner ◽  
Jun Cheng ◽  
Dongwu Lai ◽  
...  
Keyword(s):  
Oxidative Stress ◽  
Ventricular Myocytes ◽  
Ionic Current ◽  
Reversal Potential ◽  
Mechanical Stretch ◽  
Early Afterdepolarizations ◽  
Rat Ventricular Myocytes ◽  
Intracellular Ca ◽  
And Oxidative Stress

Mechanical stretch and oxidative stress have been shown to prolong action potential duration (APD) and produce early afterdepolarizations (EADs). Here, we developed a simulation model to study the role of stretch-activated channel (SAC) currents in triggering EADs in ventricular myocytes under oxidative stress. We adapted our coupling clamp circuit so that a model ionic current representing the actual SAC current was injected into ventricular myocytes and added as a real-time current. This current was calculated as ISAC = GSAC * ( Vm − ESAC), where GSAC is the stretch-activated conductance, Vm is the membrane potential, and ESAC is the reversal potential. In rat ventricular myocytes, application of GSAC did not produce sustained automaticity or EADs, although turn-on of GSAC did produce some transient automaticity at high levels of GSAC. Exposure of myocytes to 100 μM H2O2 induced significant APD prolongation and increase in intracellular Ca2+ load and transient, but no EAD or sustained automaticity was generated in the absence of GSAC. However, the combination of GSAC and H2O2 consistently produced EADs at lower levels of GSAC (2.6 ± 0.4 nS, n = 14, P < 0.05). Pacing myocytes at a faster rate further prolonged APD and promoted the development of EADs. SAC activation plays an important role in facilitating the development of EADs in ventricular myocytes under acute oxidative stress. This mechanism may contribute to the increased propensity to lethal ventricular arrhythmias seen in cardiomyopathies, where the myocardium stretch and oxidative stress generally coexist.

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