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Hnatiuk AP, Briganti F, Staudt DW, Mercola M. Human iPSC modeling of heart disease for drug development. Cell Chem Biol 2021; 28:271-282. [PMID: 33740432 PMCID: PMC8054828 DOI: 10.1016/j.chembiol.2021.02.016] [Citation(s) in RCA: 24] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/06/2020] [Revised: 01/26/2021] [Accepted: 02/19/2021] [Indexed: 02/08/2023]
Abstract
Human induced pluripotent stem cells (hiPSCs) have emerged as a promising platform for pharmacogenomics and drug development. In cardiology, they make it possible to produce unlimited numbers of patient-specific human cells that reproduce hallmark features of heart disease in the culture dish. Their potential applications include the discovery of mechanism-specific therapeutics, the evaluation of safety and efficacy in a human context before a drug candidate reaches patients, and the stratification of patients for clinical trials. Although this new technology has the potential to revolutionize drug discovery, translational hurdles have hindered its widespread adoption for pharmaceutical development. Here we discuss recent progress in overcoming these hurdles that should facilitate the use of hiPSCs to develop new medicines and individualize therapies for heart disease.
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Affiliation(s)
- Anna P Hnatiuk
- Stanford Cardiovascular Institute, 240 Pasteur Drive, Biomedical Innovation Building, Palo Alto, CA 94305, USA; Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - Francesca Briganti
- Stanford Cardiovascular Institute, 240 Pasteur Drive, Biomedical Innovation Building, Palo Alto, CA 94305, USA; Department of Medicine, Stanford University, Stanford, CA 94305, USA
| | - David W Staudt
- Stanford Cardiovascular Institute, 240 Pasteur Drive, Biomedical Innovation Building, Palo Alto, CA 94305, USA; Department of Pediatrics, Stanford University, Stanford, CA 94305, USA
| | - Mark Mercola
- Stanford Cardiovascular Institute, 240 Pasteur Drive, Biomedical Innovation Building, Palo Alto, CA 94305, USA; Department of Medicine, Stanford University, Stanford, CA 94305, USA.
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Martinez ME, Walton RD, Bayer JD, Haïssaguerre M, Vigmond EJ, Hocini M, Bernus O. Role of the Purkinje-Muscle Junction on the Ventricular Repolarization Heterogeneity in the Healthy and Ischemic Ovine Ventricular Myocardium. Front Physiol 2018; 9:718. [PMID: 29962961 PMCID: PMC6010581 DOI: 10.3389/fphys.2018.00718] [Citation(s) in RCA: 11] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/30/2018] [Accepted: 05/24/2018] [Indexed: 01/23/2023] Open
Abstract
Alteration of action potential duration (APD) heterogeneity contributes to arrhythmogenesis. Purkinje-muscle junctions (PMJs) present differential electrophysiological properties including longer APD. The goal of this study was to determine if Purkinje-related or myocardial focal activation modulates ventricular repolarization differentially in healthy and ischemic myocardium. Simultaneous epicardial (EPI) and endocardial (ENDO) optical mapping was performed on sheep left ventricular (LV) wedges with intact free-running Purkinje network (N = 7). Preparations were paced on either ENDO or EPI surfaces, or the free-running Purkinje fibers (PFs), mimicking normal activation. EPI and ENDO APDs were assessed for each pacing configuration, before and after (7 min) of the onset of no-flow ischemia. Experiments were supported by simulations. In control conditions, maximal APD was found at endocardial PMJ sites. We observed a significant transmural APD gradient for PF pacing with PMJ APD = 347 ± 41 ms and EPI APD = 273 ± 36 ms (p < 0.001). A similar transmural gradient was observed when pacing ENDO (49 ± 31 ms; p = 0.005). However, the gradient was reduced when pacing EPI (37 ± 20 ms; p = 0.005). Global dispersion of repolarization was the most pronounced for EPI pacing. In ischemia, both ENDO and EPI APD were reduced (p = 0.005) and the transmural APD gradient (109 ± 55 ms) was increased when pacing ENDO compared to control condition or when pacing EPI (p < 0.05). APD maxima remained localized at functional PMJs during ischemia. Local repolarization dispersion was significantly higher at the PMJ than at other sites. The results were consistent with simulations. We found that the activation sequence modulates repolarization heterogeneity in the ischemic sheep LV. PMJs remain active following ischemia and exert significant influence on local repolarization patterns.
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Affiliation(s)
- Marine E Martinez
- Centre de Recherche Cardio-Thoracique de Bordeaux, Université de Bordeaux, Bordeaux, France.,INSERM U1045, Centre de Recherche Cardio-Thoracique de Bordeaux, Bordeaux, France.,IHU Liryc, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Bordeaux, France
| | - Richard D Walton
- Centre de Recherche Cardio-Thoracique de Bordeaux, Université de Bordeaux, Bordeaux, France.,INSERM U1045, Centre de Recherche Cardio-Thoracique de Bordeaux, Bordeaux, France.,IHU Liryc, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Bordeaux, France
| | - Jason D Bayer
- Centre de Recherche Cardio-Thoracique de Bordeaux, Université de Bordeaux, Bordeaux, France.,UMR5251, Centre National De La Recherche Scientifique, Institut de Mathématiques de Bordeaux, Bordeaux, France
| | - Michel Haïssaguerre
- Centre de Recherche Cardio-Thoracique de Bordeaux, Université de Bordeaux, Bordeaux, France.,INSERM U1045, Centre de Recherche Cardio-Thoracique de Bordeaux, Bordeaux, France.,IHU Liryc, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Bordeaux, France.,Centre Hospitalier Universitaire, Bordeaux University Hospital, Hopital Cardiologique du Haut Lévèque, Bordeaux, France
| | - Edward J Vigmond
- Centre de Recherche Cardio-Thoracique de Bordeaux, Université de Bordeaux, Bordeaux, France.,UMR5251, Centre National De La Recherche Scientifique, Institut de Mathématiques de Bordeaux, Bordeaux, France
| | - Mélèze Hocini
- Centre de Recherche Cardio-Thoracique de Bordeaux, Université de Bordeaux, Bordeaux, France.,INSERM U1045, Centre de Recherche Cardio-Thoracique de Bordeaux, Bordeaux, France.,IHU Liryc, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Bordeaux, France.,Centre Hospitalier Universitaire, Bordeaux University Hospital, Hopital Cardiologique du Haut Lévèque, Bordeaux, France
| | - Olivier Bernus
- Centre de Recherche Cardio-Thoracique de Bordeaux, Université de Bordeaux, Bordeaux, France.,INSERM U1045, Centre de Recherche Cardio-Thoracique de Bordeaux, Bordeaux, France.,IHU Liryc, Electrophysiology and Heart Modeling Institute, Fondation Bordeaux Université, Bordeaux, France
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van Dongen IM, Elias J, Meijborg VM, De Bakker JM, Limpens J, Conrath CE, Henriques JP. Electrocardiographic changes after successful recanalization of a chronic total coronary occlusion. A systematic review and meta-analysis. CARDIOVASCULAR REVASCULARIZATION MEDICINE 2018; 19:221-228. [DOI: 10.1016/j.carrev.2017.09.004] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/2017] [Accepted: 09/05/2017] [Indexed: 12/21/2022]
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Bonomini MP, Arini PD. Modulation of spatial variance of ventricular repolarization after myocardial infarction. Biomed Signal Process Control 2017. [DOI: 10.1016/j.bspc.2017.01.014] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Arini PD, Baglivo FH, Martínez JP, Laguna P. Evaluation of ventricular repolarization dispersion during acute myocardial ischemia: spatial and temporal ECG indices. Med Biol Eng Comput 2014; 52:375-91. [PMID: 24474594 DOI: 10.1007/s11517-014-1136-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/06/2013] [Accepted: 01/16/2014] [Indexed: 01/28/2023]
Abstract
In this work, we studied the evolution of different electrocardiogram (ECG) indices of ventricular repolarization dispersion (VRD) during acute transmural myocardial ischemia in 95 patients undergoing percutaneous coronary intervention (PCI). We studied both temporal indices of VRD (T-VRD), based on the time intervals of the ECG wave, and spatial indices of VRD (S-VRD), based on the eigenvalues of the spatial correlation matrix of the ECG. The T-wave peak-to-end interval I(TPE) index showed statistically significant differences during left anterior descending artery and right coronary artery (RCA) occlusion for almost the complete time course of the PCI procedure with respect to the control recording. Regarding S-VRD indices, we observed statistically significant increases in the ratio of second to the first eigenvalue I(T21), the ratio of the third to the first eigenvalue I(T31) and the T-wave residuum I(TWR) during RCA occlusions. We also found a statistically significant increase in the I(T31) during left circumflex artery occlusions. To evaluate the evolution of VRD indices during acute ischemia, we calculated the relative change parameter R(I) for each index I. Maximal relative changes (R(I)) during acute ischemia were found for the S-VRD indices I(T21), the first eigenvalue I(λ1) and the second eigenvalue I(λ2), with changes 64, 57 and 52 times their baseline range of variation during the control recording, respectively. Also, we found that relative changes with respect to the baseline were higher in patients with T-wave alternans (TWA) than in those without TWA. In conclusion, results suggest that I(TPE) as well as I(T21), I(T31) and I(TWR) are very responsive to dispersion changes induced by ischemia, but with a behavior which very much depends on the occluded artery.
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Affiliation(s)
- Pedro David Arini
- Argentine Institute of Mathematics, 'Alberto P. Calderón' (CONICET), Saavedra 15, C1083ACA, Buenos Aires, Argentina,
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6
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Beat-to-beat ventricular repolarization variability evaluated during acute myocardial ischemia. Biomed Signal Process Control 2013. [DOI: 10.1016/j.bspc.2013.08.002] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
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7
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Light-dark dependence of electrocardiographic changes during asphyxia and reoxygenation in a rat model. Open Med (Wars) 2010. [DOI: 10.2478/s11536-010-1038-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
AbstractThe aim of this study was to evaluate the effect of ventilation on electrocardiographic time intervals as a function of the light-dark (LD) cycle in an in vivo rat model. RR, PQ, QT and QTc intervals were measured in female Wistar rats anaesthetized with both ketamine and xylazine (100 mg/15 mg/kg, i.m., open chest experiments) after adaptation to the LD cycle (12:12h) for 4 weeks. Electrocardiograms (ECG) were recorded before surgical interventions; after tracheotomy, and thoracotomy, and 5 minutes of stabilization with artificial ventilation; 30, 60, 90 and 120 seconds after the onset of apnoea; and after 5, 10, 15, and 20 minutes of artificial reoxygenation. Time intervals in intact animals showed significant LD differences, except in the QT interval. The initial significant (p<0,001) LD differences in PQ interval and loss of dependence on LD cycle in the QT interval were preserved during short-term apnoea-induced asphyxia (30–60 sec) In contrast, long-term asphyxia (90–120 sec) eliminated LD dependence in the PQ interval, but significant LD differences were shown in the QT interval. Apnoea completely abolished LD differences in the RR interval. Reoxygenation restored the PQ and QT intervals to the pre-asphyxic LD differences, but with the RR intervals, the LD differences were eliminated. We have concluded that myocardial vulnerability is dependent on the LD cycle and on changes of pulmonary ventilation.
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9
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Coronel R, Wilms-Schopman FJ, Opthof T, Janse MJ. Dispersion of repolarization and arrhythmogenesis. Heart Rhythm 2009; 6:537-43. [DOI: 10.1016/j.hrthm.2009.01.013] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/20/2008] [Accepted: 01/09/2009] [Indexed: 11/25/2022]
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Arini PD, Bertrán GC, Valverde ER, Laguna P. T-wave width as an index for quantification of ventricular repolarization dispersion: Evaluation in an isolated rabbit heart model. Biomed Signal Process Control 2008. [DOI: 10.1016/j.bspc.2007.10.001] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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11
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Shimoni Y, Liu XF. Gender differences in ANG II levels and action on multiple K+ current modulation pathways in diabetic rats. Am J Physiol Heart Circ Physiol 2004; 287:H311-9. [PMID: 15087286 DOI: 10.1152/ajpheart.01212.2003] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Gender differences were studied in ventricular myocytes from insulin-deficient (Type 1) diabetic rats. Cells were obtained by enzymatic dispersion of hearts from control male and female rats and from rats made diabetic with streptozotocin (100 mg/kg) 7-14 days before experiments. ANG II content, measured by ELISA, was augmented in diabetic males but unaltered in diabetic females. In diabetic ovariectomized females, ANG II levels were augmented as in males. ANG II affects multiple cellular pathways including activation of protein kinase C (PKC) and several tyrosine kinases as well as inhibition of protein kinase A (PKA). The involvement of these pathways in modulating outward K(+) currents was studied. Transient and sustained outward K(+) currents were measured using the whole cell voltage-clamp method. In males, these currents are attenuated under diabetic conditions but are augmented by the ANG II-converting enzyme inhibitor quinapril. Activation of PKA by 8-bromo-cAMP enhanced both K(+) currents in cells from diabetic males. The augmentation of these currents by quinapril was blocked when PKA inhibition was maintained with the Rp isomer of 3',5'-cyclic monophosphorothioate. Inhibition of tyrosine kinases by genistein also augmented K(+) currents in cells from diabetic males. Action potentials were abbreviated by 8-bromo-cAMP and genistein. However, both genistein and 8-bromo-cAMP had no effect on K(+) currents in cells from diabetic females. In cells from ovariectomized diabetic females, 8-bromo-cAMP and genistein enhanced these K(+) currents as in males. Inhibition of PKC augmented the transient and sustained K(+) currents in cells from diabetic males and females. A contribution of non-ANG II-dependent activation of PKC is suggested. These results describe some of the mechanisms that may underlie gender-specific differences in the development of cardiac disease and arrhythmias.
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Affiliation(s)
- Yakhin Shimoni
- Cardiovascular Research Group, Department of Physiology and Biophysics, University of Calgary, Alberta, Canada T2N 4N1.
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Shimoni Y, Chuang M, Abel ED, Severson DL. Gender-dependent attenuation of cardiac potassium currents in type 2 diabetic db/db mice. J Physiol 2003; 555:345-54. [PMID: 14694146 PMCID: PMC1664833 DOI: 10.1113/jphysiol.2003.055590] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Single ventricular myocytes were prepared from control db/+ and insulin-resistant diabetic db/db male mice at 6 and 12 weeks of age. Peak and sustained outward potassium currents were measured using whole-cell voltage clamp methods. At 6 weeks currents were fully developed in control and diabetic mice, with no differences in the density of either current. By 12 weeks both currents were significantly attenuated in the diabetic mice, but could be augmented by in vitro incubation with the angiotensin-converting enzyme (ACE) inhibitor quinapril (1 microM, 5-9 h). In cells from female db/db mice (12 weeks of age), K(+) currents were not attenuated and no effects of quinapril were observed. To investigate whether lack of insulin action accounts for these gender differences, cells were also isolated from cardiomyocyte-specific insulin receptor knockout (CIRKO) mice. Both K(+) currents were significantly attenuated in cells from male and female CIRKO mice, and action potentials were significantly prolonged. Incubation with quinapril did not augment K(+) currents. Our results demonstrate that type 2 diabetes is associated with gender-selective attenuation of K(+) currents in cardiomyocytes, which may underlie gender differences in the development of some cardiac arrhythmias. The mechanism for attenuation of K(+) currents in cells from male mice is due, at least in part, to an autocrine effect resulting from activation of a cardiac renin-angiotensin system. Insulin is not involved in these gender differences, since the absence of insulin action in CIRKO mice diminishes K(+) currents in cells from both males and females.
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Affiliation(s)
- Yakhin Shimoni
- Department of Physiology and Biophysics, Health Sciences Centre, 3330 Hospital Dr N.W., Calgary AB, Canada T2N 4N1.
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Shimoni Y, Liu XF. Sex differences in the modulation of K+ currents in diabetic rat cardiac myocytes. J Physiol 2003; 550:401-12. [PMID: 12777446 PMCID: PMC2343038 DOI: 10.1113/jphysiol.2003.041269] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/07/2003] [Accepted: 04/28/2003] [Indexed: 11/08/2022] Open
Abstract
A transient (Ipeak) and a sustained (Isus) outward K+ current were measured, using whole-cell voltage-clamp methods, in isolated rat ventricular myocytes obtained by enzymatic dispersion. A comparison was made between male and female rats following induction of (insulin-deficient) diabetes with streptozotocin (STZ). In control (non-diabetic) rats, both currents were smaller in cells obtained from females, as compared to males (P<0.005). However, whereas inducing diabetes in male rats significantly attenuated both Ipeak and Isus (P<0.005), Ipeak was unchanged in female diabetic rats. Isus was significantly (P<0.005) reduced, but the extent of reduction was smaller (P<0.02) than in males. The formation of angiotensin II (ATII) or endothelin-1 (ET-1) was blocked using inhibitors of angiotensin-converting enzyme (ACE) and endothelin-converting enzyme (ECE), respectively. In cells from diabetic males both inhibitors significantly (P<0.005) enhanced K+ currents. In contrast, no effect was observed in cells from female diabetic rats. However, in ovariectomized (Ovx) diabetic females the in vitro inhibition of ATII and ET-1 formation augmented the two K+ currents, but not when oestradiol was administered in vivo prior to cell isolation. In cells from diabetic males, incubation with 100 nM 17beta-oestradiol significantly (P<0.005) enhanced both Ipeak and Isus. This effect was blocked if ATII or ET-1 was added to the medium. These results show that autocrine modulation of K+ currents by renin-angiotensin and endothelin systems is attenuated or absent in female diabetic rats. Oestradiol plays a key role in reducing this modulation. These results may underlie some of the sex differences associated with development of cardiac arrhythmias.
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Affiliation(s)
- Yakhin Shimoni
- Cardiovascular Research Group, Department of Physiology and Biophysics, University of Calgary, Alberta, Canada T2N 4N1.
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Shimoni Y, Liu XF. Role of PKC in autocrine regulation of rat ventricular K+ currents by angiotensin and endothelin. Am J Physiol Heart Circ Physiol 2003; 284:H1168-81. [PMID: 12626328 DOI: 10.1152/ajpheart.00748.2002] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Transient and sustained K(+) currents were measured in isolated rat ventricular myocytes obtained from control, steptozotocin-induced (Type 1) diabetic, and hypothyroid rats. Both currents, attenuated by the endocrine abnormalities, were significantly augmented by in vitro incubation (>6 h) with the angiotensin-converting enzyme inhibitor quinapril or the angiotensin II (ANG II) receptor blocker saralasin. Western blots indicated a parallel increase in Kv4.2 and Kv1.2, channel proteins that underlie the transient and (part of the) sustained currents. Under diabetic and hypothyroid conditions, both currents were also augmented by an endothelin receptor blocker (PD142893) or by an endothelin-converting enzyme inhibitor. Kv4.2 density was also enhanced by PD142893. Incubation (>5 h) with the PKC inhibitor bis-indolylmaleimide augmented both currents, whereas the PKC activator dioctanoyl-rac-glycerol (DiC8) prevented the augmentation of currents by quinapril. DiC8 also prevented the augmentation of Kv4.2 density by quinapril. Specific peptides that activate PKC translocation indicated that PKC-epsilon and not PKC-delta is involved in ANG II action on these currents. In control myocytes, quinapril and PD142893 augmented the sustained late current but had no effect on peak current. It is concluded that an autocrine release of angiotensin and endothelin in diabetic and hypothyroid conditions attenuates K(+) currents by suppressing the synthesis of some K(+) channel proteins, with the effects mediated at least partially by PKC-epsilon.
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Affiliation(s)
- Yakhin Shimoni
- Cardiovascular Research Group, Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada T2N 4N1.
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Abstract
Torsade de pointes (Tdp) is a polymorphic ventricular tachycardia (VT) in which the axis of the QRS complex changes direction after a certain number of complexes as if the complex rotated around the baseline. Tdp is usually associated with QT prolongation, and dispersion of ventricular repolarlization (DR). Experimental models of tdp are usually associated with induction of early after depolarizations (EADs). Several aspects of the pathogenesis of tdp are incompletely understood. The purpose of this article is to propose the directions in research that may increase our current understanding of the factors responsible for tdp. The most plausible hypotheses requiring further supporting evidence are: 1. The occurrence of tdp requires the presence of DR i.e. tdp does not occur in the absence of DR. 2. EADs appear to play an important role as a trigger to tdp in the animal models, but more evidence are needed at the clinical level. 3. EADs may be responsible for arrhythmias other than tdp. 4. The greater incidence of tdp in the females than in tha males may be attributed to differences in the duration of the QT interval and different morphology of the ST-segment and the T-wave. The above gender differences may be caused by the effects of gonadal hormones which modulate some of the membrane currents flowing during early ventricular repolarization.
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Affiliation(s)
- Borys Surawicz
- Krannert Institute of Cardiology, Indiana University School of Medicine, Indianapolis, Indiana, USA.
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Shimoni Y. Inhibition of the formation or action of angiotensin II reverses attenuated K+ currents in type 1 and type 2 diabetes. J Physiol 2001; 537:83-92. [PMID: 11711563 PMCID: PMC2278945 DOI: 10.1111/j.1469-7793.2001.0083k.x] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/21/2022] Open
Abstract
1. Transient and sustained calcium-independent outward K(+) currents (I(t) and I(SS)) as well as action potentials were recorded in cardiac ventricular myocytes isolated from two models of diabetes mellitus. 2. Rats injected (I.V.) with streptozotocin (STZ, 100 mg kg(-1)) 6-10 days before cell isolation developed insulin-dependent (type 1) diabetes. I(t) and I(SS) were attenuated and the action potential prolonged. Incubation of myocytes (6-9 h) with the angiotensin II (ATII) receptor blockers saralasin or valsartan (1 microM) significantly augmented these currents. Inclusion of valsartan (1 g l(-1)) in the drinking water for 5-10 days prior to and following STZ injection partially prevented current attenuation. 3. Incubation of myocytes from STZ-treated rats (6-9 h) with 1 microM quinapril, an angiotensin-converting enzyme (ACE) inhibitor, significantly augmented I(t) and I(SS) and shortened the ventricular action potential. I(t) augmentation was not due to changes in steady-state inactivation or in recovery from inactivation. No acute effects of quinapril were observed. 4. The effects of quinapril and valsartan were abolished by 2 microM cycloheximide. 5. Myocytes were isolated from the db/db mouse, a leptin receptor mutant that develops symptoms of non-insulin-dependent (type 2) diabetes. K+ currents in these cells were also attenuated, and the action potentials prolonged. Incubation of these cells (> 6 h) with valsartan (1 microM) significantly enhanced the transient and sustained outward currents. 6. These results confirm recent suggestions that cardiac myocytes contain a renin-angiotensin system, which is activated in diabetes. It is proposed that chronic release of ATII leads to changes in ionic currents and action potentials, which can be reversed by blocking the formation or action of ATII. This may underlie the proven benefits of ATII receptor blockade or ACE inhibition in diabetes, by providing protection against cardiac arrhythmias.
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Affiliation(s)
- Y Shimoni
- Department of Physiology and Biophysics, Cardiovascular Research Group, University of Calgary, 3330 Hospital Drive NW, Calgary, Alberta, Canada T2N 4N1.
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Shimoni Y, Rattner JB. Type 1 diabetes leads to cytoskeleton changes that are reflected in insulin action on rat cardiac K(+) currents. Am J Physiol Endocrinol Metab 2001; 281:E575-85. [PMID: 11500313 DOI: 10.1152/ajpendo.2001.281.3.e575] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
A sustained K(+) current (I(ss)) is attenuated in ventricular cells from streptozotocin (STZ)-induced diabetic rats. The in vitro addition of insulin to isolated cells augments I(ss) in a process that is blocked by disrupting either actin microfilaments (with cytochalasin D) or microtubules (with colchicine). When these agents are added at progressively later times, the effect of insulin becomes evident in a time-dependent manner. I(ss) is also augmented by insulin in control cells in a cytoskeleton-dependent manner. However, in contrast to diabetic cells, cytoskeleton-dependent augmentation of I(ss) by insulin occurs at a considerably faster rate in control cells. Immunofluorescent labeling shows a reduced density of beta-tubulin in diabetic cells, particularly in perinuclear regions. In vitro insulin replacement or in vivo insulin injections given to STZ-treated rats enhances beta-tubulin density. These results suggest an impairment of cytoskeleton function and structure under insulin-deficient conditions, which may have implications for cardiac function.
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Affiliation(s)
- Y Shimoni
- Department of Physiology and Biophysics, University of Calgary Health Sciences Centre, 3330 Hospital Dr. NW, Calgary, Alberta, Canada T2N 4N1.
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Thorneloe KS, Liu XF, Walsh MP, Shimoni Y. Transmural differences in rat ventricular protein kinase C epsilon correlate with its functional regulation of a transient cardiac K+ current. J Physiol 2001; 533:145-54. [PMID: 11351023 PMCID: PMC2278612 DOI: 10.1111/j.1469-7793.2001.0145b.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The effects of PKC activation on a transient (It) and a sustained (Iss) cardiac K+ current and the subcellular distribution of the epsilon isoform of PKC (PKC(epsilon)) were compared in epicardial and endocardial regions of the rat ventricle. Activation of PKC(epsilon) with a diacylglycerol analogue (di-octanoyl-glycerol (DiC8), 20 (mu)M) leads to differential effects in epicardial and endocardial cells. In epicardial cells (n = 20) It and Iss are attenuated by 17.7 +/- 2.1 % and 11.9 +/- 3.1 %, respectively (means +/- S.E.M.). In endocardial cells It attenuation was significantly smaller (4.6 +/- 1.6 %, n = 14, P < 0.0005). Iss attenuation was similar to that in epicardial cells (10.5 +/- 3.8 %). PKC[epsilon] expression was measured by Western blotting. Calculated endocardial/epicardial ratios showed no regional differences in total protein extracts (1.04 +/- 0.11, mean +/- S.E.M, n = 4), but PKC[epsilon] distribution in the cytosolic fraction showed a marked difference, with significantly (P < 0.05) higher levels in endocardial extracts. The cytosolic endocardial/epicardial PKC[epsilon] ratio was 2.64 +/- 0.24 (n = 4), indicating a reduced amount of PKC[epsilon] in the membrane fraction of the endocardium. This could account for the reduced effect of DiC8 on It in endocardial myocytes. Under both hypothyroid and streptozotocin-induced diabetic conditions the difference in endocardial and epicardial cytosolic PKC[epsilon] levels was absent (ratios of 0.86 +/- 0.21 (n = 4) and 1.09 +/- 0.16 (n = 3), respectively; means +/- S.E.M.). Ratios in the total protein extracts were not significantly different from those in control conditions. The results show transmural differences in the functional effects of PKC(epsilon) activation on a cardiac K+ current, and in the subcellular distribution of PKC(epsilon). These differences are absent in diabetic and hypothyroid conditions.
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Affiliation(s)
- K S Thorneloe
- Department of Biochemistry and Molecular Biology, Canadian Institute of Health Research Group in Regulation of Vascular Contractility, Calgary, Alberta, Canada
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Akar FG, Laurita KR, Rosenbaum DS. Cellular basis for dispersion of repolarization underlying reentrant arrhythmias. J Electrocardiol 2001; 33 Suppl:23-31. [PMID: 11265727 DOI: 10.1054/jelc.2000.20313] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Substantial heterogeneity in ion channel density and expression exists in cells isolated from various regions of the heart. Cell-to-cell coupling in the intact heart, however, is expected to attenuate the functional expression of the ion channel heterogeneities. Due to limitations of conventional electrophysiological recording techniques, the extent to which cellular electrical heterogeneities are functionally present in intact myocardium remains unknown. High-resolution optical mapping with voltage-sensitive dyes was used to measure transepicardial and transmural repolarization gradients in the Langendorff perfused guinea pig ventricle and the canine wedge preperation, respectively. Diversity of repolarization kinetics in the transepicardial direction modulated dispersion of repolarization in a biphasic fashion as premature coupling interval was shortened. Moreover, modulation of repolarization paralleled arrhythmia vulnerability in a predictable fashion. Transmural optical mapping revealed significant gradients of repolarization across the ventricular wall that were markedly increased in a surrogate model of LQTS. Transmural gradients of repolarization in LQTS were associated with an enhanced susceptibility to TdP. Therefore, despite strong cell-to-cell coupling in the normal heart, heterogeneities in the ionic make-up of cells across the epicardial and transmural surfaces result in functional heterogeneities of repolarization leading to arrhythmias.
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Affiliation(s)
- F G Akar
- Department of Medicine, Heart and Vascular Research Center, Case Western Reserve University, Cleveland, OH 44109-1998, USA
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Shimoni Y, Severson D, Ewart HS. Insulin resistance and the modulation of rat cardiac K(+) currents. Am J Physiol Heart Circ Physiol 2000; 279:H639-49. [PMID: 10924063 DOI: 10.1152/ajpheart.2000.279.2.h639] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
K(+) currents were measured using a whole cell voltage-clamp method in enzymatically isolated rat ventricular myocytes obtained from two hyperinsulinemic, insulin-resistant models. Fructose-fed rats as well as genetically obese rats, both of which are resistant to the metabolic effects of insulin, were used. The normal augmentation of a calcium-independent sustained K(+) current was reduced or abolished in insulin-resistant states. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadyl sulfate (3-4 wk treatment or after 5-6 h in vitro) enhanced the sustained K(+) current. The in vitro effect of vanadyl was blocked by cycloheximide. Insulin resistance of the K(+) current was not reversed by vanadyl sulfate. The results show that insulin resistance is expressed in terms of insulin actions on ion channels, in addition to its actions on metabolism. This resistance can be reversed by the insulin-sensitizing drug metformin. Vanadate compounds, which mimic the effects of insulin on metabolism, also mimic the augmenting effects of insulin on a cardiac K(+) current in a manner suggesting synthesis of new channels.
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Affiliation(s)
- Y Shimoni
- Department of Physiology and Biophysics, University of Calgary, Calgary, Alberta, Canada T2N 4N1.
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Abstract
QT dispersion was proposed as an index of the spatial inhomogeneity of ventricular recovery times. The results of studies that found significant correlation between dispersion of ventricular recovery times measured with monophasic action potentials and QT dispersion were interpreted as proof of the direct link between QT dispersion and the dispersion of ventricular recovery times. Later it was shown that QT dispersion is not a direct reflection of the spatial variation of the recovery times and cannot be used for quantification of this variation. The interlead variability of the QT intervals is a result of different projections of the spatial T-wave loop into the various electrocardiographic leads. The reliability of both manual and automatic measurement of QT dispersion is low and is often of the order of the differences of Qt dispersion between different patient groups. The measurement reliability is influenced by intrinsic factors (e.g., amplitude of the T wave) and extrinsic factors (e.g., noise, paper speed of recording, instruments for manual measurements, and type of algorithm and interalgorithmic settings for automatic measurement). There is very little to choose between the different indices of expression of QT dispersion, as well as between the different lead configurations used for its measurement. QT dispersion is not simply a result of measurement error, but a crude measure of abnormalities during the whole course of repolarization. Only grossly prolonged QT dispersion (e.g., > or =100 ms), must be interpreted simply as a sign of the abnormal course of the repolarization, and inferences about the actual dispersion of the ventricular recovery times should not be made. Newer concepts of assessment of the morphology of the T wave are already emerging and will probably be of higher clinical value.
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Affiliation(s)
- V Batchvarov
- Department of Cardiological Sciences, St. George's Hospital Medical School, London, United Kingdom
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Shimoni Y. Hormonal control of cardiac ion channels and transporters. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 1999; 72:67-108. [PMID: 10446502 DOI: 10.1016/s0079-6107(99)00005-x] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/01/2023]
Affiliation(s)
- Y Shimoni
- Department of Physiology and Biophysics, Faculty of Medicine, University of Calgary, Alta., Canada.
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