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Swaminathan PD, Purohit A, Hund TJ, Anderson ME. Calmodulin-dependent protein kinase II: linking heart failure and arrhythmias. Circ Res 2012; 110:1661-77. [PMID: 22679140 DOI: 10.1161/circresaha.111.243956] [Citation(s) in RCA: 215] [Impact Index Per Article: 17.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
Understanding relationships between heart failure and arrhythmias, important causes of suffering and sudden death, remains an unmet goal for biomedical researchers and physicians. Evidence assembled over the past decade supports a view that activation of the multifunctional Ca(2+) and calmodulin-dependent protein kinase II (CaMKII) favors myocardial dysfunction and cell membrane electrical instability. CaMKII activation follows increases in intracellular Ca(2+) or oxidation, upstream signals with the capacity to transition CaMKII into a Ca(2+) and calmodulin-independent constitutively active enzyme. Constitutively active CaMKII appears poised to participate in disease pathways by catalyzing the phosphorylation of classes of protein targets important for excitation-contraction coupling and cell survival, including ion channels and Ca(2+) homeostatic proteins, and transcription factors that drive hypertrophic and inflammatory gene expression. This rich diversity of downstream targets helps to explain the potential for CaMKII to simultaneously affect mechanical and electrical properties of heart muscle cells. Proof-of-concept studies from a growing number of investigators show that CaMKII inhibition is beneficial for improving myocardial performance and for reducing arrhythmias. We review the molecular physiology of CaMKII and discuss CaMKII actions at key cellular targets and results of animal models of myocardial hypertrophy, dysfunction, and arrhythmias that suggest CaMKII inhibition may benefit myocardial function while reducing arrhythmias.
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Affiliation(s)
- Paari Dominic Swaminathan
- Division of Cardiovascular Medicine, Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, IA 52242, USA
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52
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Roberts BN, Yang PC, Behrens SB, Moreno JD, Clancy CE. Computational approaches to understand cardiac electrophysiology and arrhythmias. Am J Physiol Heart Circ Physiol 2012; 303:H766-83. [PMID: 22886409 DOI: 10.1152/ajpheart.01081.2011] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/13/2023]
Abstract
Cardiac rhythms arise from electrical activity generated by precisely timed opening and closing of ion channels in individual cardiac myocytes. These impulses spread throughout the cardiac muscle to manifest as electrical waves in the whole heart. Regularity of electrical waves is critically important since they signal the heart muscle to contract, driving the primary function of the heart to act as a pump and deliver blood to the brain and vital organs. When electrical activity goes awry during a cardiac arrhythmia, the pump does not function, the brain does not receive oxygenated blood, and death ensues. For more than 50 years, mathematically based models of cardiac electrical activity have been used to improve understanding of basic mechanisms of normal and abnormal cardiac electrical function. Computer-based modeling approaches to understand cardiac activity are uniquely helpful because they allow for distillation of complex emergent behaviors into the key contributing components underlying them. Here we review the latest advances and novel concepts in the field as they relate to understanding the complex interplay between electrical, mechanical, structural, and genetic mechanisms during arrhythmia development at the level of ion channels, cells, and tissues. We also discuss the latest computational approaches to guiding arrhythmia therapy.
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Affiliation(s)
- Byron N Roberts
- Tri-Institutional MD-PhD Program, Physiology, Biophysics and Systems Biology Graduate Program, Weill Cornell Medical College/The Rockefeller University/Sloan-Kettering Cancer Institute, Weill Medical College of Cornell University, New York, New York, USA
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53
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Ziv O, Schofield L, Lau E, Chaves L, Patel D, Jeng P, Peng X, Choi BR, Koren G. A novel, minimally invasive, segmental myocardial infarction with a clear healed infarct borderzone in rabbits. Am J Physiol Heart Circ Physiol 2012; 302:H2321-30. [PMID: 22447944 DOI: 10.1152/ajpheart.00031.2012] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Ventricular arrhythmias in the setting of a healed myocardial infarction have been studied to a much lesser degree than acute and subacute infarction, due to the pericardial scarring, which results from the traditional open-chest techniques used for myocardial infarction (MI) induction. We sought to develop a segmental MI with low perioperative mortality in the rabbit that allows optimal visualization and therefore improved study of the infarction borderzone. Rabbits underwent MI using endovascular coil occlusion of the first obtuse marginal artery. Three weeks postprocedure, we evaluated our model by echocardiography and electrophysiology studies, optical mapping of isolated hearts, and histological studies. Seventeen rabbits underwent the protocol (12 MI and 5 sham) with a 92% survival to completion of the study (11 MI and 5 sham). MI rabbits demonstrated wall motion abnormalities on echocardiography while shams did not. At electrophysiological study, two MI rabbits had inducible ventricular tachycardia and one had inducible ventricular fibrillation. Isolated hearts demonstrated no pericardial scarring with a smooth, easily identifiable infarct borderzone. Optical mapping of the borderzone region showed successful mapping of peri-infarct reentry formation, with ventricular fibrillation inducible in 11 of 11 MI hearts and 1 of 5 sham hearts. We demonstrate successful high resolution mapping in the borderzone, showing delayed conduction in this region corresponding to late deflections in the QRS on ECG. We report the successful development of a minimally invasive MI via targeted coil delivery to the obtuse marginal artery with an exceptionally high rate of procedural survival and an arrhythmogenic phenotype. This model mimics human post-MI on echocardiography, gross pathology, histology, and electrophysiology.
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Affiliation(s)
- Ohad Ziv
- Cardiovascular Research Center, Rhode Island Hospital, Warren Alpert Medical School of Brown University, Providence, USA
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54
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Maier LS. Ca2+/Calmodulin-Dependent Protein Kinase II (CaMKII) in the Heart. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2012; 740:685-702. [DOI: 10.1007/978-94-007-2888-2_30] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
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Shahin R, Taha MO. Elaborate ligand-based modeling and subsequent synthetic exploration unveil new nanomolar Ca2+/calmodulin-dependent protein kinase II inhibitory leads. Bioorg Med Chem 2012; 20:377-400. [PMID: 22112539 DOI: 10.1016/j.bmc.2011.10.071] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/22/2011] [Revised: 10/23/2011] [Accepted: 10/25/2011] [Indexed: 10/15/2022]
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Models of HERG gating. Biophys J 2011; 101:631-42. [PMID: 21806931 DOI: 10.1016/j.bpj.2011.06.050] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2011] [Revised: 06/22/2011] [Accepted: 06/27/2011] [Indexed: 11/21/2022] Open
Abstract
HERG (Kv11.1, KCNH2) is a voltage-gated potassium channel with unique gating characteristics. HERG has fast voltage-dependent inactivation, relatively slow deactivation, and fast recovery from inactivation. This combination of gating kinetics makes study of HERG difficult without using mathematical models. Several HERG models have been developed, with fundamentally different organization. HERG is the molecular basis of I(Kr), which plays a critical role in repolarization. We programmed and compared five distinct HERG models. HERG gating cannot be adequately replicated using Hodgkin-Huxley type formulation. Using Markov models, a five-state model is required with three closed, one open, and one inactivated state, and a voltage-independent step between some of the closed states. A fundamental difference between models is the presence/absence of a transition directly from the proximal closed state to the inactivated state. The only models that effectively reproduce HERG data have no direct closed-inactivated transition, or have a closed-inactivated transition that is effectively zero compared to the closed-open transition, rendering the closed-inactivation transition superfluous. Our single-channel model demonstrates that channels can inactivate without conducting with a flickering or bursting open-state. The various models have qualitative and quantitative differences that are critical to accurate predictions of HERG behavior during repolarization, tachycardia, and premature depolarizations.
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Erickson JR, He BJ, Grumbach IM, Anderson ME. CaMKII in the cardiovascular system: sensing redox states. Physiol Rev 2011; 91:889-915. [PMID: 21742790 DOI: 10.1152/physrev.00018.2010] [Citation(s) in RCA: 176] [Impact Index Per Article: 13.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The multifunctional Ca(2+)- and calmodulin-dependent protein kinase II (CaMKII) is now recognized to play a central role in pathological events in the cardiovascular system. CaMKII has diverse downstream targets that promote vascular disease, heart failure, and arrhythmias, so improved understanding of CaMKII signaling has the potential to lead to new therapies for cardiovascular disease. CaMKII is a multimeric serine-threonine kinase that is initially activated by binding calcified calmodulin (Ca(2+)/CaM). Under conditions of sustained exposure to elevated Ca(2+)/CaM, CaMKII transitions into a Ca(2+)/CaM-autonomous enzyme by two distinct but parallel processes. Autophosphorylation of threonine-287 in the CaMKII regulatory domain "traps" CaMKII into an open configuration even after Ca(2+)/CaM unbinding. More recently, our group identified a pair of methionines (281/282) in the CaMKII regulatory domain that undergo a partially reversible oxidation which, like autophosphorylation, prevents CaMKII from inactivating after Ca(2+)/CaM unbinding. Here we review roles of CaMKII in cardiovascular disease with an eye to understanding how CaMKII may act as a transduction signal to connect pro-oxidant conditions into specific downstream pathological effects that are relevant to rare and common forms of cardiovascular disease.
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Affiliation(s)
- Jeffrey R Erickson
- Department of Pharmacology, University of California at Davis, Davis, California 95616, USA.
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58
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Erickson JR, Patel R, Ferguson A, Bossuyt J, Bers DM. Fluorescence resonance energy transfer-based sensor Camui provides new insight into mechanisms of calcium/calmodulin-dependent protein kinase II activation in intact cardiomyocytes. Circ Res 2011; 109:729-38. [PMID: 21835909 DOI: 10.1161/circresaha.111.247148] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
RATIONALE Calcium/calmodulin-dependent protein kinase II (CaMKII) is a key mediator of intracellular signaling in the heart. However, the tools currently available for assessing dynamic changes in CaMKII localization and activation in living myocytes are limited. OBJECTIVE We use Camui, a novel FRET-based biosensor in which full-length CaMKII is flanked by CFP and YFP, to measure CaMKII activation state in living rabbit myocytes. METHODS AND RESULTS We show that Camui and mutant variants that lack the sites of CaMKII autophosphorylation (T286A) and oxidative regulation (CM280/1VV) serve as useful biosensors for CaMKIIδ activation state. Camui (wild-type or mutant) was expressed in isolated adult cardiac myocytes, and localization and CaMKII activation state were determined using confocal microscopy. Camui, like CaMKIIδ, is concentrated at the z-lines, with low baseline activation state. Camui activation increased directly with pacing frequency, but the maximal effect was blunted with the T286A, consistent with frequency-dependent phosphorylation of CaMKII at T286 mainly at high-frequency and high-amplitude Ca transients. Camui was also activated by 4 neurohormonal agonists. Angiotensin II and endothelin-1 activated Camui, largely through an oxidation-dependent mechanism, whereas isoproterenol- and phenylephrine-mediated mechanisms had a significant autophosphorylation-dependent component. CONCLUSIONS Camui is a novel, nondestructive tool that allows spatiotemporally resolved measurement of CaMKII activation state in physiologically functioning myocytes. This represents a first step in using Camui to elucidate key mechanistic details of CaMKII signaling in live hearts and myocytes.
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Affiliation(s)
- Jeffrey R Erickson
- Department of Pharmacology, University of California, Davis, CA 95616-8636, USA
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59
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Sarkar AX, Sobie EA. Quantification of repolarization reserve to understand interpatient variability in the response to proarrhythmic drugs: a computational analysis. Heart Rhythm 2011; 8:1749-55. [PMID: 21699863 DOI: 10.1016/j.hrthm.2011.05.023] [Citation(s) in RCA: 84] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2011] [Accepted: 05/27/2011] [Indexed: 01/08/2023]
Abstract
BACKGROUND "Repolarization reserve" is frequently invoked to explain why potentially proarrhythmic drugs cause, across a population, a range of changes to cardiac action potentials (APs). However, the mechanisms underlying this interindividual variability are not understood quantitatively. OBJECTIVE The purpose of this study was to perform a novel analysis of mathematical models of ventricular myocytes to quantify repolarization reserve and gain insight into the factors responsible for variability in the response to proarrhythmic drugs. METHODS/RESULTS In several models of human or canine ventricular myocytes, variability was simulated by randomizing model parameters and running repeated simulations. With each randomly generated set of parameters, APs before and after simulated 75% block of the rapid delayed rectifier current (I(Kr)) were calculated. Multivariable regression was performed to determine how much each model parameter attenuated or exacerbated the AP prolongation caused by the I(Kr)-blocking drug. Simulations with a human ventricular myocyte model suggest that drug response is influenced most strongly by (1) the density of I(Kr), (2) the density of slow delayed rectifier current I(Ks), (3) the voltage dependence of I(Kr) inactivation, (4) the density of L-type Ca2+ current, and (5) the kinetics of I(Ks) activation. The analysis also identified mechanisms underlying nonintuitive behavior, such as ionic currents that prolong baseline APs but decrease drug-induced AP prolongation. Finally, the simulations provided quantitative insight into conditions that aggravate the drug response, such as silent ion channel mutations and heart failure. CONCLUSION These modeling results provide the first thorough quantification of repolarization reserve and improve our understanding of interindividual variability in adverse drug reactions.
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Affiliation(s)
- Amrita X Sarkar
- Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, New York 10029, USA
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60
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Wu L, Ma J, Li H, Wang C, Grandi E, Zhang P, Luo A, Bers DM, Shryock JC, Belardinelli L. Late sodium current contributes to the reverse rate-dependent effect of IKr inhibition on ventricular repolarization. Circulation 2011; 123:1713-20. [PMID: 21482963 DOI: 10.1161/circulationaha.110.000661] [Citation(s) in RCA: 86] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
BACKGROUND The reverse rate dependence (RRD) of actions of I(Kr)-blocking drugs to increase the action potential duration (APD) and beat-to-beat variability of repolarization (BVR) of APD is proarrhythmic. We determined whether inhibition of endogenous, physiological late Na(+) current (late I(Na)) attenuates the RRD and proarrhythmic effect of I(Kr) inhibition. METHODS AND RESULTS Duration of the monophasic APD (MAPD) was measured from female rabbit hearts paced at cycle lengths from 400 to 2000 milliseconds, and BVR was calculated. In the absence of a drug, duration of monophasic action potential at 90% completion of repolarization (MAPD(90)) and BVR increased as the cycle length was increased from 400 to 2000 milliseconds (n=36 and 26; P<0.01). Both E-4031 (20 nmol/L) and d-sotalol (10 μmol/L) increased MAPD(90) and BVR at all stimulation rates, and the increase was greater at slower than at faster pacing rates (n=19, 11, 12 and 7, respectively; P<0.01). Tetrodotoxin (1 μmol/L) and ranolazine significantly attenuated the RRD of MAPD(90,) reduced BVR (P<0.01), and abolished torsade de pointes in hearts treated with either 20 nmol/L E-4031 or 10 μmol/L d-sotalol. Endogenous late I(Na) in cardiomyocytes stimulated at cycle lengths from 500 to 4000 milliseconds was greater at slower than at faster stimulation rates, and rapidly decreased during the first several beats at faster but not at slower rates (n=8; P<0.01). In a computational model, simulated RRD of APD caused by E-4031 and d-sotalol was attenuated when late I(Na) was inhibited. CONCLUSION Endogenous late I(Na) contributes to the RRD of I(Kr) inhibitor-induced increases in APD and BVR and to bradycardia-related ventricular arrhythmias.
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Affiliation(s)
- Lin Wu
- Department of Biology, Gilead Sciences, 1651 Page Mill Road, Palo Alto, CA 94304, USA.
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61
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Huang RYC, Laing JG, Kanter EM, Berthoud VM, Bao M, Rohrs HW, Townsend RR, Yamada KA. Identification of CaMKII phosphorylation sites in Connexin43 by high-resolution mass spectrometry. J Proteome Res 2011; 10:1098-109. [PMID: 21158428 PMCID: PMC3171746 DOI: 10.1021/pr1008702] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Connexin43 (Cx43) is a major cardiac gap junction channel protein required for normal electrical and contractile activity. Gap junction channel assembly, function, and turnover are regulated by phosphorylation under both normal and disease conditions. The carboxyl terminus (CT) of Cx43 contains numerous amino acid residues that are phosphorylated by protein kinases. However, our knowledge of the specific residues and kinases involved is incomplete. The objective of this study was to identify amino acid residues in the Cx43-CT that are targets of the multifunctional protein kinase, Ca(2+)/calmodulin protein kinase II (CaMKII), an enzyme known to play critical roles in Ca(2+) homeostasis, transcription, apoptosis, and ischemic heart disease. We subjected fusion protein containing the Cx43-CT to phosphorylation by CaMKII in vitro, digestion with Lys-C and trypsin followed by enrichment for phosphorylated peptides using TiO(2), and analysis in an LTQ XL Orbitrap with collision-induced dissociation and electron transfer dissociation. We deduced the sites of modification by interpreting tandem spectra from these "orthogonal" methods of gas phase peptide fragmentation. We have identified 15 serine residues, including one novel site, in the Cx43-CT that are phosphorylated by CaMKII, the activity of which may be important in regulating Cx43 in normal and diseased hearts.
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Affiliation(s)
| | - James G. Laing
- Department of Medicine, Washington University School of Medicine
- Center for Cardiovascular Research, Washington University School of Medicine
| | - Evelyn M. Kanter
- Department of Medicine, Washington University School of Medicine
- Center for Cardiovascular Research, Washington University School of Medicine
| | | | - Mingwei Bao
- Department of Medicine, Washington University School of Medicine
- Center for Cardiovascular Research, Washington University School of Medicine
| | - Henry W. Rohrs
- Department of Chemistry, Washington University School of Medicine
| | - R. Reid Townsend
- Department of Medicine, Washington University School of Medicine
| | - Kathryn A. Yamada
- Department of Medicine, Washington University School of Medicine
- Center for Cardiovascular Research, Washington University School of Medicine
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Local control of β-adrenergic stimulation: Effects on ventricular myocyte electrophysiology and Ca(2+)-transient. J Mol Cell Cardiol 2011; 50:863-71. [PMID: 21345340 DOI: 10.1016/j.yjmcc.2011.02.007] [Citation(s) in RCA: 102] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/19/2010] [Revised: 02/03/2011] [Accepted: 02/09/2011] [Indexed: 11/21/2022]
Abstract
Local signaling domains and numerous interacting molecular pathways and substrates contribute to the whole-cell response of myocytes during β-adrenergic stimulation (βARS). We aimed to elucidate the quantitative contribution of substrates and their local signaling environments during βARS to the canine epicardial ventricular myocyte electrophysiology and calcium transient (CaT). We present a computational compartmental model of βARS and its electrophysiological effects. Novel aspects of the model include localized signaling domains, incorporation of β1 and β2 receptor isoforms, a detailed population-based approach to integrate the βAR and Ca(2+)/Calmodulin kinase (CaMKII) signaling pathways and their effects on a wide range of substrates that affect whole-cell electrophysiology and CaT. The model identifies major roles for phosphodiesterases, adenylyl cyclases, PKA and restricted diffusion in the control of local cAMP levels and shows that activation of specific cAMP domains by different receptor isoforms allows for specific control of action potential and CaT properties. In addition, the model predicts increased CaMKII activity during βARS due to rate-dependent accumulation and increased Ca(2+) cycling. CaMKII inhibition, reduced compartmentation, and selective blockade of β1AR is predicted to reduce the occurrence of delayed afterdepolarizations during βARS. Finally, the relative contribution of each PKA substrate to whole-cell electrophysiology is quantified by comparing simulations with and without phosphorylation of each target. In conclusion, this model enhances our understanding of localized βAR signaling and its whole-cell effects in ventricular myocytes by incorporating receptor isoforms, multiple pathways and a detailed representation of multiple-target phosphorylation; it provides a basis for further studies of βARS under pathological conditions.
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63
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Yang JH, Saucerman JJ. Computational models reduce complexity and accelerate insight into cardiac signaling networks. Circ Res 2011; 108:85-97. [PMID: 21212391 DOI: 10.1161/circresaha.110.223602] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Cardiac signaling networks exhibit considerable complexity in size and connectivity. The intrinsic complexity of these networks complicates the interpretation of experimental findings. This motivates new methods for investigating the mechanisms regulating cardiac signaling networks and the consequences these networks have on cardiac physiology and disease. Next-generation experimental techniques are also generating a wealth of genomic and proteomic data that can be difficult to analyze or interpret. Computational models are poised to play a key role in addressing these challenges. Computational models have a long history in contributing to the understanding of cardiac physiology and are useful for identifying biological mechanisms, inferring multiscale consequences to cell signaling activities and reducing the complexity of large data sets. Models also integrate well with experimental studies to explain experimental observations and generate new hypotheses. Here, we review the contributions computational modeling approaches have made to the analysis of cardiac signaling networks and forecast opportunities for computational models to accelerate cardiac signaling research.
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Affiliation(s)
- Jason H Yang
- Department of Biomedical Engineering, Robert M. Berne Cardiovascular Research Center, University of Virginia, Charlottesville, 22908, USA
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64
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Singh MV, Anderson ME. Is CaMKII a link between inflammation and hypertrophy in heart? J Mol Med (Berl) 2011; 89:537-43. [PMID: 21279501 DOI: 10.1007/s00109-011-0727-5] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2010] [Revised: 12/09/2010] [Accepted: 01/13/2011] [Indexed: 10/18/2022]
Abstract
Myocardial infarction is a major cause of morbidity and mortality in the developing and developed world. Although current interventions have been successful in prolonging life, they are inadequate because mortality is still high among MI patients. The multifunctional Ca(2+)/calmodulin-dependent protein kinase (CaMKII) plays a key role in the structure and contractility of the myocardium. CaMKII activity is increased in MI hearts and CaMKII promotes cardiac hypertrophy and inflammation, processes consistently activated by myocardial injury. Hypertrophy and inflammation are also related to neurohumoral and redox signaling which uncouple CaMKII activation from Ca(2+)/calmodulin dependence. Thus, CaMKII may act as a nodal point for integrating hypertrophic and inflammatory signaling in myocardium.
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Affiliation(s)
- Madhu V Singh
- Department of Internal Medicine, Carver College of Medicine, University of Iowa, Iowa City, 52242, USA.
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65
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Soltis AR, Saucerman JJ. Synergy between CaMKII substrates and β-adrenergic signaling in regulation of cardiac myocyte Ca(2+) handling. Biophys J 2011; 99:2038-47. [PMID: 20923637 DOI: 10.1016/j.bpj.2010.08.016] [Citation(s) in RCA: 72] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2009] [Revised: 07/23/2010] [Accepted: 08/04/2010] [Indexed: 01/10/2023] Open
Abstract
Cardiac excitation-contraction coupling is a highly coordinated process that is controlled by protein kinase signaling pathways, including Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) and protein kinase A (PKA). Increased CaMKII expression and activity (as occurs during heart failure) destabilizes EC coupling and may lead to sudden cardiac death. To better understand mechanisms of cardiac CaMKII function, we integrated dynamic CaMKII-dependent regulation of key Ca(2+) handling targets with previously validated models of cardiac EC coupling, Ca(2+)/calmodulin-dependent activation of CaMKII, and β-adrenergic activation of PKA. Model predictions are validated against CaMKII-overexpression data from rabbit ventricular myocytes. The model demonstrates how overall changes to Ca(2+) handling during CaMKII overexpression are explained by interactions between individual CaMKII substrates. CaMKII and PKA activities during β-adrenergic stimulation may synergistically facilitate inotropic responses and contribute to a CaMKII-Ca(2+)-CaMKII feedback loop. CaMKII regulated early frequency-dependent acceleration of relaxation and EC coupling gain (which was highly sarcoplasmic reticulum Ca(2+) load-dependent). Additionally, the model identifies CaMKII-dependent ryanodine receptor hyperphosphorylation as a proarrhythmogenic trigger. In summary, we developed a detailed computational model of CaMKII and PKA signaling in cardiac myocytes that provides unique insights into their regulation of normal and pathological Ca(2+) handling.
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Affiliation(s)
- Anthony R Soltis
- Department of Biomedical Engineering, University of Virginia, Charlottesville, VA, USA
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66
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Sarkar AX, Sobie EA. Regression analysis for constraining free parameters in electrophysiological models of cardiac cells. PLoS Comput Biol 2010; 6:e1000914. [PMID: 20824123 PMCID: PMC2932676 DOI: 10.1371/journal.pcbi.1000914] [Citation(s) in RCA: 95] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/14/2010] [Accepted: 07/31/2010] [Indexed: 11/17/2022] Open
Abstract
A major challenge in computational biology is constraining free parameters in mathematical models. Adjusting a parameter to make a given model output more realistic sometimes has unexpected and undesirable effects on other model behaviors. Here, we extend a regression-based method for parameter sensitivity analysis and show that a straightforward procedure can uniquely define most ionic conductances in a well-known model of the human ventricular myocyte. The model's parameter sensitivity was analyzed by randomizing ionic conductances, running repeated simulations to measure physiological outputs, then collecting the randomized parameters and simulation results as "input" and "output" matrices, respectively. Multivariable regression derived a matrix whose elements indicate how changes in conductances influence model outputs. We show here that if the number of linearly-independent outputs equals the number of inputs, the regression matrix can be inverted. This is significant, because it implies that the inverted matrix can specify the ionic conductances that are required to generate a particular combination of model outputs. Applying this idea to the myocyte model tested, we found that most ionic conductances could be specified with precision (R(2) > 0.77 for 12 out of 16 parameters). We also applied this method to a test case of changes in electrophysiology caused by heart failure and found that changes in most parameters could be well predicted. We complemented our findings using a Bayesian approach to demonstrate that model parameters cannot be specified using limited outputs, but they can be successfully constrained if multiple outputs are considered. Our results place on a solid mathematical footing the intuition-based procedure simultaneously matching a model's output to several data sets. More generally, this method shows promise as a tool to define model parameters, in electrophysiology and in other biological fields.
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Affiliation(s)
- Amrita X Sarkar
- Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, New York, USA
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Wolf RM, Mitchell CC, Christensen MD, Mohler PJ, Hund TJ. Defining new insight into atypical arrhythmia: a computational model of ankyrin-B syndrome. Am J Physiol Heart Circ Physiol 2010; 299:H1505-14. [PMID: 20729400 DOI: 10.1152/ajpheart.00503.2010] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Normal cardiac excitability depends on the coordinated activity of specific ion channels and transporters within specialized domains at the plasma membrane and sarcoplasmic reticulum. Ion channel dysfunction due to congenital or acquired defects has been linked to human cardiac arrhythmia. More recently, defects in ion channel-associated proteins have been associated with arrhythmia. Ankyrin-B is a multifunctional adapter protein responsible for targeting select ion channels, transporters, cytoskeletal proteins, and signaling molecules in excitable cells, including neurons, pancreatic β-cells, and cardiomyocytes. Ankyrin-B dysfunction has been linked to cardiac arrhythmia in human patients and ankyrin-B heterozygous (ankyrin-B(+/-)) mice with a phenotype characterized by sinus node dysfunction, susceptibility to ventricular arrhythmias, and sudden death ("ankyrin-B syndrome"). At the cellular level, ankyrin-B(+/-) cells have defects in the expression and membrane localization of the Na(+)/Ca(2+) exchanger and Na(+)-K(+)-ATPase, Ca(2+) overload, and frequent afterdepolarizations, which likely serve as triggers for lethal cardiac arrhythmias. Despite knowledge gathered from mouse models and human patients, the molecular mechanism responsible for cardiac arrhythmias in the setting of ankyrin-B dysfunction remains unclear. Here, we use mathematical modeling to provide new insights into the cellular pathways responsible for Ca(2+) overload and afterdepolarizations in ankyrin-B(+/-) cells. We show that the Na(+)/Ca(2+) exchanger and Na(+)-K(+)-ATPase play related, yet distinct, roles in intracellular Ca(2+) accumulation, sarcoplasmic reticulum Ca(2+) overload, and afterdepolarization generation in ankyrin-B(+/-) cells. These findings provide important insights into the molecular mechanisms underlying a human disease and are relevant for acquired human arrhythmia, where ankyrin-B dysfunction has recently been identified.
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Affiliation(s)
- Roseanne M Wolf
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa 52242, USA
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Abstract
Calcium/calmodulin-dependent kinase II (CaMKII) is a multifunctional serine/threonine kinase expressed abundantly in the heart. CaMKII targets numerous proteins involved in excitation-contraction coupling and excitability, and its activation may simultaneously contribute to heart failure and cardiac arrhythmias. In this review, we summarize the modulatory effects of CaMKII on cardiac ion channel function and expression and illustrate potential implications in the onset of arrhythmias via a computer model.
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69
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Decker KF, Rudy Y. Ionic mechanisms of electrophysiological heterogeneity and conduction block in the infarct border zone. Am J Physiol Heart Circ Physiol 2010; 299:H1588-97. [PMID: 20709867 DOI: 10.1152/ajpheart.00362.2010] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The increased incidence of arrhythmia in the healing phase after infarction has been linked to remodeling in the epicardial border zone (EBZ). Ionic models of normal zone (NZ) and EBZ myocytes were incorporated into one-dimensional models of propagation to gain mechanistic insights into how ion channel remodeling affects action potential (AP) duration (APD) and refractoriness, vulnerability to conduction block, and conduction safety postinfarction. We found that EBZ tissue exhibited abnormal APD restitution. The remodeled Na(+) current (I(Na)) and L-type Ca(2+) current (I(Ca,L)) promoted increased effective refractory period and prolonged APD at a short diastolic interval. While postrepolarization refractoriness due to remodeled EBZ I(Na) was the primary determinant of the vulnerable window for conduction block at the NZ-to-EBZ transition in response to premature S2 stimuli, altered EBZ restitution also promoted APD dispersion and increased the vulnerable window at fast S1 pacing rates. Abnormal EBZ APD restitution and refractoriness also led to abnormal periodic conduction block patterns for a range of fast S1 pacing rates. In addition, we found that I(Na) remodeling decreased conduction safety in the EBZ but that inward rectifier K(+) current remodeling partially offset this decrease. EBZ conduction was characterized by a weakened AP upstroke and short intercellular delays, which prevented I(Ca,L) and transient outward K(+) current remodeling from playing a role in EBZ conduction in uncoupled tissue. Simulations of a skeletal muscle Na(+) channel SkM1-I(Na) injection into the EBZ suggested that this recently proposed antiarrhythmic therapy has several desirable effects, including normalization of EBZ effective refractory period and APD restitution, elimination of vulnerability to conduction block, and normalization of conduction in tissue with reduced intercellular coupling.
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Affiliation(s)
- Keith F Decker
- Cardiac Bioelectricity and Arrhythmia Center, Department of Biomedical Engineering, Washington University, St. Louis, Missouri 63130-4899, USA.
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70
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Christensen MD, Dun W, Boyden PA, Anderson ME, Mohler PJ, Hund TJ. Oxidized calmodulin kinase II regulates conduction following myocardial infarction: a computational analysis. PLoS Comput Biol 2009; 5:e1000583. [PMID: 19997488 PMCID: PMC2778128 DOI: 10.1371/journal.pcbi.1000583] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Accepted: 10/30/2009] [Indexed: 01/05/2023] Open
Abstract
Calmodulin kinase II (CaMKII) mediates critical signaling pathways responsible for divergent functions in the heart including calcium cycling, hypertrophy and apoptosis. Dysfunction in the CaMKII signaling pathway occurs in heart disease and is associated with increased susceptibility to life-threatening arrhythmia. Furthermore, CaMKII inhibition prevents cardiac arrhythmia and improves heart function following myocardial infarction. Recently, a novel mechanism for oxidative CaMKII activation was discovered in the heart. Here, we provide the first report of CaMKII oxidation state in a well-validated, large-animal model of heart disease. Specifically, we observe increased levels of oxidized CaMKII in the infarct border zone (BZ). These unexpected new data identify an alternative activation pathway for CaMKII in common cardiovascular disease. To study the role of oxidation-dependent CaMKII activation in creating a pro-arrhythmia substrate following myocardial infarction, we developed a new mathematical model of CaMKII activity including both oxidative and autophosphorylation activation pathways. Computer simulations using a multicellular mathematical model of the cardiac fiber demonstrate that enhanced CaMKII activity in the infarct BZ, due primarily to increased oxidation, is associated with reduced conduction velocity, increased effective refractory period, and increased susceptibility to formation of conduction block at the BZ margin, a prerequisite for reentry. Furthermore, our model predicts that CaMKII inhibition improves conduction and reduces refractoriness in the BZ, thereby reducing vulnerability to conduction block and reentry. These results identify a novel oxidation-dependent pathway for CaMKII activation in the infarct BZ that may be an effective therapeutic target for improving conduction and reducing heterogeneity in the infarcted heart. Calmodulin kinase II (CaMKII) is a multifunctional serine/threonine kinase that regulates diverse functions in heart. Recently, a novel pathway for CaMKII activation was discovered where oxidation of the kinase at specific methionine residues produces persistent activity. This alternative oxidation-dependent pathway has important implications for heart disease where oxidative stress is increased (e.g., heart failure and following myocardial infarction). We hypothesized that myocardial infarction caused by occlusion of a coronary artery would increase levels of oxidized CaMKII. Moreover, we hypothesized that oxidative CaMKII activation represents an important mechanistic link between increased oxidative stress and life-threatening heart rhythm disturbances (arrhythmias) in heart disease. We report a dramatic increase in levels of oxidized CaMKII following myocardial infarction in the canine. Based on these experimental data, we developed a novel mathematical model of CaMKII activity to study the role of oxidation-dependent CaMKII activation in regulating cardiac cell excitability. Our findings identify a novel role for oxidation-dependent CaMKII activation following myocardial infarction and provide a mechanistic link between oxidative stress and lethal cardiac arrhythmias in heart disease.
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Affiliation(s)
- Matthew D Christensen
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa Carver College of Medicine, Iowa City, Iowa, United States of America
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Decker KF, Heijman J, Silva JR, Hund TJ, Rudy Y. Properties and ionic mechanisms of action potential adaptation, restitution, and accommodation in canine epicardium. Am J Physiol Heart Circ Physiol 2009; 296:H1017-26. [PMID: 19168720 DOI: 10.1152/ajpheart.01216.2008] [Citation(s) in RCA: 87] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
Computational models of cardiac myocytes are important tools for understanding ionic mechanisms of arrhythmia. This work presents a new model of the canine epicardial myocyte that reproduces a wide range of experimentally observed rate-dependent behaviors in cardiac cell and tissue, including action potential (AP) duration (APD) adaptation, restitution, and accommodation. Model behavior depends on updated formulations for the 4-aminopyridine-sensitive transient outward current (I(to1)), the slow component of the delayed rectifier K(+) current (I(Ks)), the L-type Ca(2+) channel current (I(Ca,L)), and the Na(+)-K(+) pump current (I(NaK)) fit to data from canine ventricular myocytes. We found that I(to1) plays a limited role in potentiating peak I(Ca,L) and sarcoplasmic reticulum Ca(2+) release for propagated APs but modulates the time course of APD restitution. I(Ks) plays an important role in APD shortening at short diastolic intervals, despite a limited role in AP repolarization at longer cycle lengths. In addition, we found that I(Ca,L) plays a critical role in APD accommodation and rate dependence of APD restitution. Ca(2+) entry via I(Ca,L) at fast rate drives increased Na(+)-Ca(2+) exchanger Ca(2+) extrusion and Na(+) entry, which in turn increases Na(+) extrusion via outward I(NaK). APD accommodation results from this increased outward I(NaK). Our simulation results provide valuable insight into the mechanistic basis of rate-dependent phenomena important for determining the heart's response to rapid and irregular pacing rates (e.g., arrhythmia). Accurate simulation of rate-dependent phenomena and increased understanding of their mechanistic basis will lead to more realistic multicellular simulations of arrhythmia and identification of molecular therapeutic targets.
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Affiliation(s)
- Keith F Decker
- Cardiac Bioelectricity and Arrhythmia Center, Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, Missouri, USA
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Hund TJ, Wright PJ, Dun W, Snyder JS, Boyden PA, Mohler PJ. Regulation of the ankyrin-B-based targeting pathway following myocardial infarction. Cardiovasc Res 2008; 81:742-9. [PMID: 19074823 DOI: 10.1093/cvr/cvn348] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
AIMS Ion channel reorganization is a critical step in the pro-arrhythmogenic remodelling process that occurs in heart disease. Ankyrin-B (AnkB) is required for targeting and stabilizing ion channels, exchangers, and pumps. Despite a wealth of knowledge implicating the importance of AnkB in human cardiovascular physiology, nothing is known regarding the role of AnkB in common forms of acquired human disease. METHODS AND RESULTS We present the first report of AnkB regulation following myocardial infarction (MI). AnkB protein levels were reduced in the infarct border zone 5 days following coronary artery occlusion in the canine. We also observed a dramatic increase in AnkB mRNA levels 5 days post-occlusion. Surprisingly, the expression of the upstream AnkB cytoskeletal component beta2-spectrin was unchanged in post-infarct tissues. However, protein levels and/or membrane expression of downstream AnkB-associated ion channels and transporters Na+/K+ ATPase, Na+/Ca2+ exchanger, and IP3 receptor were altered 5 days post-occlusion. Interestingly, protein levels of the protein phosphatase 2A, an AnkB-associated signalling protein, were significantly affected 5 days post-occlusion. AnkB and PP2A protein levels recovered by 14 days post-occlusion, whereas Na+/K+ ATPase levels recovered by 2 months post-occlusion. CONCLUSION These findings reveal the first evidence of ankyrin remodelling following MI and suggest an unexpected divergence point for regulation between ankyrin and the underlying cytoskeletal network. These findings suggest a logical, but unexpected, molecular mechanism underlying ion channel and transporter remodelling following MI.
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Affiliation(s)
- Thomas J Hund
- Department of Internal Medicine, Division of Cardiovascular Medicine, University of Iowa Carver College of Medicine, 285 Newton Road, CBRB 2283, Iowa City, IA 52242, USA.
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