scholarly journals Genetic Loss of I K1 Causes Adrenergic-Induced Phase 3 Early Afterdepolariz ations and Polymorphic and Bidirectional Ventricular Tachycardia

2020 ◽  
Vol 13 (9) ◽  
Author(s):  
Louise Reilly ◽  
Francisco J. Alvarado ◽  
Di Lang ◽  
Sara Abozeid ◽  
Hannah Van Ert ◽  
...  
Keyword(s):  
Ventricular Tachycardia ◽  
Action Potential ◽  
Cardiac Function ◽  
Ventricular Myocytes ◽  
Optical Mapping ◽  
Adrenergic Stimulation ◽  
Phase 3 ◽  
Early Afterdepolarizations ◽  
Whole Heart

Background: Arrhythmia syndromes associated with KCNJ2 mutations have been described clinically; however, little is known of the underlying arrhythmia mechanism. We create the first patient inspired KCNJ2 transgenic mouse and study effects of this mutation on cardiac function, I K1 , and Ca 2+ handling, to determine the underlying cellular arrhythmic pathogenesis. Methods: A cardiac-specific KCNJ2 -R67Q mouse was generated and bred for heterozygosity (R67Q +/− ). Echocardiography was performed at rest, under anesthesia. In vivo ECG recording and whole heart optical mapping of intact hearts was performed before and after adrenergic stimulation in wild-type (WT) littermate controls and R67Q +/− mice. I K1 measurements, action potential characterization, and intracellular Ca 2+ imaging from isolated ventricular myocytes at baseline and after adrenergic stimulation were performed in WT and R67Q +/− mice. Results: R67Q +/− mice (n=17) showed normal cardiac function, structure, and baseline electrical activity compared with WT (n=10). Following epinephrine and caffeine, only the R67Q +/− mice had bidirectional ventricular tachycardia, ventricular tachycardia, frequent ventricular ectopy, and/or bigeminy and optical mapping demonstrated high prevalence of spontaneous and sustained ventricular arrhythmia. Both R67Q +/− (n=8) and WT myocytes (n=9) demonstrated typical n-shaped I K1 IV relationship; however, following isoproterenol, max outward I K1 increased by ≈20% in WT but decreased by ≈24% in R67Q +/− ( P <0.01). R67Q +/− myocytes (n=5) demonstrated prolonged action potential duration at 90% repolarization and after 10 nmol/L isoproterenol compared with WT (n=7; P <0.05). Ca 2+ transient amplitude, 50% decay rate, and sarcoplasmic reticulum Ca 2+ content were not different between WT (n=18) and R67Q +/− (n=16) myocytes. R67Q +/− myocytes (n=10) under adrenergic stimulation showed frequent spontaneous development of early afterdepolarizations that occurred at phase 3 of action potential repolarization. Conclusions: KCNJ2 mutation R67Q +/− causes adrenergic-dependent loss of I K1 during terminal repolarization and vulnerability to phase 3 early afterdepolarizations. This model clarifies a heretofore unknown arrhythmia mechanism and extends our understanding of treatment implications for patients with KCNJ2 mutation.

scholarly journals MCU Overexpression Rescues Inotropy and Reverses Heart Failure by Reducing SR Ca 2+ Leak

2021 ◽  
Author(s):  
Ting Liu ◽  
Ni Yang ◽  
Agnieszka Sidor ◽  
Brian O'Rourke
Keyword(s):  
Oxidative Stress ◽  
Heart Failure ◽  
Cardiac Function ◽  
Ventricular Myocytes ◽  
Interstitial Fibrosis ◽  
Left Ventricular ◽  
Viral Gene ◽  
Adrenergic Stimulation ◽  
Guinea Pig Model

Rationale: In heart failure (HF), impaired sarcoplasmic reticulum (SR) Ca 2+ release and cytosolic Na + overload depress mitochondrial Ca 2+ (mCa 2+ ) signaling, resulting in a diminished ability to maintain matrix NAD(P)H redox potential, leading to increased oxidative stress when workload increases. Enhancing mCa 2+ can reverse this defect but could potentially increase the likelihood of mitochondrial Ca 2+ overload. Objective: To determine if moderate mitochondrial Ca 2+ uniporter (MCU) overexpression has beneficial or detrimental effects on the development of HF and incident arrythmias in a guinea pig model (ACi) of HF and sudden cardiac death. Methods and Results: In vivo viral gene transfer was used to increase MCU levels by ~30% in ACi hearts. Left ventricular myocytes from hearts with MCU overexpression (ACi+MCU) displayed enhanced mCa 2+ uptake, decreased oxidative stress, and increased β‐adrenergic- and frequency-dependent augmentation of Ca 2+ transients and contractions, compared to myocytes from ACi hearts. MCU overexpression decreased SR Ca 2+ leak in the ACi group and mitigated the elevated ryanodine receptor disulfide crosslinks in HF. β‐adrenergic responses were blunted in isolated perfused ACi hearts and these deficiencies were normalized in ACI+MCU hearts. To examine the in vivo effects of MCU overexpression, ACi hearts were transduced with the MCU virus 2 3w after aortic constriction, at the onset of cardiac decompensation. Two weeks later, cardiac function worsened in the untreated ACi group (fractional shortening: 39{plus minus}1% at 2w and 32{plus minus}1% at 4w), whereas MCU overexpression significantly improved cardiac function (36{plus minus}1% at 2w and 42{plus minus}2% at 4w). MCU overexpression in the decompensating ACi heart also attenuated pulmonary edema and interstitial fibrosis and prevented triggered arrhythmias. Conclusions: Moderate MCU overexpression in failing hearts enhances contractility and responses to β-adrenergic stimulation in isolated myocytes and perfused hearts by inhibiting mitochondrial oxidative stress-induced SR Ca 2+ leak. MCU overexpression also reversed HF and inhibited ectopic ventricular arrhythmias.

Altered K+ current profiles underlie cardiac action potential shortening in hyperkalemia and β-adrenergic stimulation

2019 ◽  
Vol 97 (8) ◽  
pp. 773-780 ◽  
Author(s):  
Bence Hegyi ◽  
Ye Chen-Izu ◽  
Leighton T. Izu ◽  
Tamás Bányász
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Delayed Rectifier ◽  
Adrenergic Stimulation ◽  
Compensatory Mechanisms ◽  
Phase 3 ◽  
K Current ◽  
Rabbit Ventricular Myocytes ◽  
Action Potential Shortening ◽  
Stimulation Of

Hyperkalemia is known to develop in various conditions including vigorous physical exercise. In the heart, hyperkalemia is associated with action potential (AP) shortening that was attributed to altered gating of K+ channels. However, it remains unknown how hyperkalemia changes the profiles of each K+ current under a cardiac AP. Therefore, we recorded the major K+ currents (inward rectifier K+ current, IK1; rapid and slow delayed rectifier K+ currents, IKr and IKs, respectively) using AP-clamp in rabbit ventricular myocytes. As K+ may accumulate at rapid heart rates during sympathetic stimulation, we also examined the effect of isoproterenol on these K+ currents. We found that IK1 was significantly increased in hyperkalemia, whereas the reduction of driving force for K+ efflux dominated over the altered channel gating in case of IKr and IKs. Overall, the markedly increased IK1 in hyperkalemia overcame the relative decreases of IKr and IKs during AP, resulting in an increased net repolarizing current during AP phase 3. β-Adrenergic stimulation of IKs also provided further repolarizing power during sympathetic activation, although hyperkalemia limited IKs upregulation. These results indicate that facilitation of IK1 in hyperkalemia and β-adrenergic stimulation of IKs represent important compensatory mechanisms against AP prolongation and arrhythmia susceptibility.

Modulation of mouse cardiac function in vivo by eNOS and ANP

2000 ◽  
Vol 278 (3) ◽  
pp. H971-H981 ◽  
Author(s):  
Robert Gyurko ◽  
Peter Kuhlencordt ◽  
Mark C. Fishman ◽  
Paul L. Huang
Keyword(s):  
Cardiac Function ◽  
Isolated Heart ◽  
Cardiac Contractility ◽  
Enos Gene ◽  
Wild Type ◽  
Adrenergic Stimulation ◽  
Microvascular Endothelium ◽  
Ventricular Relaxation ◽  
Nos Inhibitors

To study the role of endothelial nitric oxide synthase (eNOS) in cardiac function, we compared eNOS expression, contractility, and relaxation in the left ventricles of wild-type and eNOS-deficient mice. eNOS immunostaining is localized to the macro- and microvascular endothelium throughout the myocardium in wild-type mice and is absent in eNOS−/− mice. Whereas blood pressure is elevated in eNOS−/− mice, baseline cardiac contractility (dP/d t max) is similar in wild-type and eNOS−/− mice (9,673 ± 2,447 and 9,928 ± 1,566 mmHg/s, respectively). The β-adrenergic agonist isoproterenol (Iso) at doses of ≥1 ng causes enhanced increases in dP/d t max in eNOS−/− mice compared with wild-type controls in vivo ( P < 0.01) as well as in Langendorff isolated heart preparations ( P < 0.02). β-Adrenergic receptor binding (Bmax) is not significantly different in the two groups of animals (Bmax = 41.4 ± 9.4 and 36.1 ± 5.1 fmol/mg for wild-type and eNOS−/−). Iso-stimulated ventricular relaxation is also enhanced in the eNOS−/− mice, as measured by dP/d t min in the isolated heart. However, baseline ventricular relaxation is normal in eNOS−/− mice (τ = 5.2 ± 1.0 and 5.6 ± 1.5 ms for wild-type and eNOS−/−, respectively), whereas it is impaired in wild-type mice after NOS inhibition (τ = 8.3 ± 2.4 ms). cGMP levels in the left ventricle are unaffected by eNOS gene deletion (wild-type: 3.1 ± 0.8 pmol/mg, eNOS−/−: 3.1 ± 0.6 pmol/mg), leading us to examine the level of another physiological regulator of cGMP. Atrial natriuretic peptide (ANP) expression is markedly upregulated in the eNOS−/− mice, and exogenous ANP restores ventricular relaxation in wild-type mice treated with NOS inhibitors. These results suggest that eNOS attenuates both inotropic and lusitropic responses to β-adrenergic stimulation, and it also appears to regulate baseline ventricular relaxation in conjunction with ANP.

Targeted inactivation of Gαi does not alter cardiac function or β-adrenergic sensitivity

2001 ◽  
Vol 280 (2) ◽  
pp. H569-H575 ◽  
Author(s):  
Mohit Jain ◽  
Chee Chew Lim ◽  
Kohzo Nagata ◽  
Vannessa M. Davis ◽  
David S. Milstone ◽  
...  
Keyword(s):  
Cardiac Function ◽  
Ventricular Myocytes ◽  
Ex Vivo ◽  
Cardiac Response ◽  
Similar Degree ◽  
Wild Type ◽  
Isolated Hearts ◽  
Targeted Inactivation ◽  
Contractile Performance

Inhibitory Gαi protein increases in the myocardium during hypertrophy and has been associated with β-adrenergic receptor (β-AR) desensitization, contractile dysfunction, and progression of cardiac disease. The role of Gαi proteins in mediating basal cardiac function and β-AR response in nonpathological myocardium, however, is uncertain. Transgenic mice with targeted inactivation of Gαi2 or Gαi3 were examined for in vivo cardiac function with the use of conscious echocardiography and for ex vivo cardiac response to inotropic stimulation with the use of Langendorff blood-perfused isolated hearts and adult ventricular cardiomyocytes. Echocardiography revealed that percent fractional shortening and heart rate were similar among wild-type, Gαi2 -null, and Gαi3 -null mice. Comparable baseline diastolic and contractile performance was also observed in isolated hearts and isolated ventricular myocytes from wild-type mice and mice lacking Gαi proteins. Isoproterenol infusion enhanced diastolic and contractile performance to a similar degree in wild-type, Gαi2 -null, and Gαi3 -null mice. These data demonstrate no observable role for inhibitory G proteins in mediating basal cardiac function or sensitivity to β-AR stimulation in nonpathological myocardium.

Optical mapping of late myocardial infarction in rats

2006 ◽  
Vol 290 (3) ◽  
pp. H1298-H1306 ◽  
Author(s):  
William R. Mills ◽  
Niladri Mal ◽  
Farhad Forudi ◽  
Zoran B. Popovic ◽  
Marc S. Penn ◽  
...  
Keyword(s):  
Myocardial Infarction ◽  
Ventricular Tachycardia ◽  
High Resolution ◽  
Action Potentials ◽  
Optical Mapping ◽  
Cellular Heterogeneity ◽  
Artery Ligation ◽  
Conduction Abnormalities ◽  
Mapping Techniques ◽  
Whole Heart

Late myocardial infarction (MI) is associated with ventricular arrhythmias and sudden cardiac death. The exact mechanistic relationship between abnormal cellular electrophysiology, conduction abnormalities, and arrhythmogenesis associated with late MI is not completely understood. We report a novel, rapid dye superfusion technique to enable whole heart, high-resolution optical mapping of late MI. Optical mapping of action potentials was performed in normal rats and rats with anterior MI 7 days after left anterior descending artery ligation. Hearts from normal rats exhibited normal action potentials and impulse conduction. With the use of programmed stimulation to assess arrhythmia inducibility, 29% of hearts with late MI had inducible sustained ventricular tachycardia, compared with 0% in normal rats. A causal relationship between the site of infarction, abnormal action potential conduction (i.e., block and slow conduction), and arrhythmogenesis was observed. Optical mapping techniques can be used to measure high-resolution action potentials in a whole heart model of late MI. This experimental model reproduces many of the electrophysiological characteristics (i.e., conduction slowing, block, and ventricular tachycardia) associated with MI in patients. Importantly, the results of this study can enhance our ability to understand the interplay between cellular heterogeneity, conduction abnormalities, and arrhythmogenesis associated with MI.

scholarly journals Interaction of the Joining Region in Junctophilin-2 With the L-Type Ca 2+ Channel Is Pivotal for Cardiac Dyad Assembly and Intracellular Ca 2+ Dynamics

2021 ◽  
Vol 128 (1) ◽  
pp. 92-114
Author(s):  
Polina Gross ◽  
Jaslyn Johnson ◽  
Carlos M. Romero ◽  
Deborah M. Eaton ◽  
Claire Poulet ◽  
...  
Keyword(s):  
Sarcoplasmic Reticulum ◽  
Ventricular Myocytes ◽  
Close Association ◽  
Ryanodine Receptors ◽  
Left Ventricular ◽  
Induced Mutations ◽  
Adrenergic Stimulation ◽  
T Tubules ◽  
Junctional Sarcoplasmic Reticulum

Rationale: Ca 2+ -induced Ca 2+ release (CICR) in normal hearts requires close approximation of L-type calcium channels (LTCCs) within the transverse tubules (T-tubules) and RyR (ryanodine receptors) within the junctional sarcoplasmic reticulum. CICR is disrupted in cardiac hypertrophy and heart failure, which is associated with loss of T-tubules and disruption of cardiac dyads. In these conditions, LTCCs are redistributed from the T-tubules to disrupt CICR. The molecular mechanism responsible for LTCCs recruitment to and from the T-tubules is not well known. JPH (junctophilin) 2 enables close association between T-tubules and the junctional sarcoplasmic reticulum to ensure efficient CICR. JPH2 has a so-called joining region that is located near domains that interact with T-tubular plasma membrane, where LTCCs are housed. The idea that this joining region directly interacts with LTCCs and contributes to LTCC recruitment to T-tubules is unknown. Objective: To determine if the joining region in JPH2 recruits LTCCs to T-tubules through direct molecular interaction in cardiomyocytes to enable efficient CICR. Methods and Results: Modified abundance of JPH2 and redistribution of LTCC were studied in left ventricular hypertrophy in vivo and in cultured adult feline and rat ventricular myocytes. Protein-protein interaction studies showed that the joining region in JPH2 interacts with LTCC-α1C subunit and causes LTCCs distribution to the dyads, where they colocalize with RyRs. A JPH2 with induced mutations in the joining region (mut PG1 JPH2) caused T-tubule remodeling and dyad loss, showing that an interaction between LTCC and JPH2 is crucial for T-tubule stabilization. mut PG1 JPH2 caused asynchronous Ca 2+ -release with impaired excitation-contraction coupling after β-adrenergic stimulation. The disturbed Ca 2+ regulation in mut PG1 JPH2 overexpressing myocytes caused calcium/calmodulin-dependent kinase II activation and altered myocyte bioenergetics. Conclusions: The interaction between LTCC and the joining region in JPH2 facilitates dyad assembly and maintains normal CICR in cardiomyocytes.

Mechanisms underlying early and delayed afterdepolarizations induced by catecholamines

1990 ◽  
Vol 258 (6) ◽  
pp. H1796-H1805 ◽  
Author(s):  
S. G. Priori ◽  
P. B. Corr
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Receptor Activation ◽  
Adrenergic Stimulation ◽  
Adrenergic Agonist ◽  
Beta Adrenergic ◽  
Low Concentrations ◽  
Coupling Interval ◽  
Major Factors ◽  
Extracellular Sodium

The relative influence of alpha- and beta-adrenergic receptor activation in eliciting early (EADs) and delayed (DADs) after depolarizations was assessed using intracellular microelectrode recordings in isolated adult canine ventricular myocytes. Normoxic myocytes were exposed to the alpha-adrenergic agonist phenylephrine (10(-8)-10(-6) M) or the beta-adrenergic agonist isoproterenol (10(-9)-10(-6) M) during pacing at different frequencies (0.5-4 Hz). alpha-Adrenergic stimulation resulted in a dose-dependent prolongation of action potential duration but failed to induce either EADs or DADs. beta-Adrenergic stimulation with isoproterenol at low concentrations (10(-9)-10(-8) M) induced a prolongation of the action potential, whereas higher concentrations (10(-7) and 10(-6) M) resulted in a marked shortening. Isoproterenol elicited single or multiple (2-5) DADs at concentrations from 10(-8) to 10(-6) M, with a corresponding increase in the amplitude of the DADs and decrease in the coupling interval as cells were paced at increasing rates. DADs often initiated and maintained sustained triggered rhythms that spontaneously terminated. Isoproterenol (10(-8)-10(-6) M) also elicited EADs in 80% of cells at the highest concentration utilized (10(-6) M) and at intermediate pacing frequencies (1-2 Hz). EADs often occurred with a 2:1 or 3:1 pattern. EADs and DADs induced by isoproterenol were reversibly abolished by low extracellular sodium, ryanodine (10(-6) M), or benzamil (10(-4) M), thus indicating that Ca2+ release from the sarcoplasmic reticulum and extracellular Na+ concentration are two major factors in the development of both types of afterdepolarizations. The demonstration that EADs can be induced by isoproterenol in ventricular muscle suggest a novel pathway for beta-adrenergic receptors to mediate arrhythmogenesis in the intact heart.

Ischemic preconditioning of the whole heart confers protection on subsequently isolated ventricular myocytes

2008 ◽  
Vol 294 (1) ◽  
pp. H524-H531 ◽  
Author(s):  
Glenn C. Rodrigo ◽  
Nilesh J. Samani
Keyword(s):  
Ischemic Preconditioning ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Ischemia Reperfusion ◽  
Isolated Cells ◽  
Cellular Models ◽  
Whole Heart ◽  
Intact Heart

Current cellular models of ischemic preconditioning (IPC) rely on inducing preconditioning in vitro and may not accurately represent complex pathways triggered by IPC in the intact heart. Here, we show that it is possible to precondition the intact heart and to subsequently isolate individual ventricular myocytes that retain the protection triggered by IPC. Myocytes isolated from Langendorff-perfused hearts preconditioned with three cycles of ischemia-reperfusion were exposed to metabolic inhibition and reenergization. Injury was assessed from induction of hypercontracture and loss of Ca2+ homeostasis and contractile function. IPC induced an immediate window of protection in isolated myocytes, with 64.3 ± 7.6% of IPC myocytes recovering Ca2+ homeostasis compared with 16.9 ± 2.4% of control myocytes ( P < 0.01). Similarly, 64.1 ± 5.9% of IPC myocytes recovered contractile function compared with 15.3 ± 2.2% of control myocytes ( P < 0.01). Protection was prevented by the presence of 0.5 mM 5-hydroxydecanoate during the preconditioning stimulus. This early protection disappeared after 6 h, but a second window of protection developed 24 h after preconditioning, with 54.9 ± 4.7% of preconditioned myocytes recovering Ca2+ homeostasis compared with 12.6 ± 2.9% of control myocytes ( P < 0.01). These data show that “true” IPC of the heart confers both windows of protection in the isolated myocytes, with a similar temporal relationship to in vivo preconditioning of the whole heart. The model should allow future studies in isolated cells of the protective mechanisms induced by true ischemia.

Adult rat ventricular myocytes cultured in defined medium: phenotype and electromechanical function

1993 ◽  
Vol 265 (2) ◽  
pp. H747-H754 ◽  
Author(s):  
O. Ellingsen ◽  
A. J. Davidoff ◽  
S. K. Prasad ◽  
H. J. Berger ◽  
J. P. Springhorn ◽  
...  
Keyword(s):  
Action Potential ◽  
Ventricular Myocytes ◽  
Contractile Function ◽  
Defined Medium ◽  
Resting Membrane Potential ◽  
Isolated Cells ◽  
Rat Ventricular Myocytes ◽  
Adult Rat ◽  
Alpha Actin

We studied primary short-term cultures of adult rat ventricular myocytes in defined medium to determine whether phenotype and electromechanical function are maintained in rod-shaped, quiescent cells. Although > 80% of the myocytes retained their rod-shaped in vivo morphology for up to 72 h, contractile function as measured by cell edge motion declined 30-50% from 6 to 24 h, paralleling a 68% shortening of action potential duration. From 24 to 72 h, contractility remained unchanged. Ca2+ channel current density increased 55% after 24-48 h and then returned to the level of freshly isolated cells (9 +/- 1 pA/pF, mean +/- SE). Resting membrane potential (-71 +/- 1 mV) and action potential overshoot (34 +/- 3 mV) did not change. The ratio of alpha- to beta-myosin heavy chain mRNA and the level of cardiac alpha-actin mRNA were maintained for 8 days. Thus quiescent adult rat ventricular myocytes in defined medium undergo extensive phenotypic adaptation within 72 h of isolation, despite maintenance of a rod-shaped morphology and stable levels of contractile protein mRNA, which may limit their suitability for electrophysiological and contractile function studies.

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