151
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Pedersen TH, Gurung IS, Grace A, Huang CLH. Calmodulin kinase II initiates arrhythmogenicity during metabolic acidification in murine hearts. Acta Physiol (Oxf) 2009; 197:13-25. [PMID: 19416122 PMCID: PMC2774152 DOI: 10.1111/j.1748-1716.2009.01991.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Aim: The multifunctional signal molecule calmodulin kinase II (CaMKII) has been associated with cardiac arrhythmogenesis under conditions where its activity is chronically elevated. Recent studies report that its activity is also acutely elevated during acidosis. We test a hypothesis implicating CaMKII in the arrhythmogenesis accompanying metabolic acidification. Methods: We obtained monophasic action potential recordings from Langendorff-perfused whole heart preparations and single cell action potentials (AP) using whole-cell patch-clamped ventricular myocytes. Spontaneous sarcoplasmic reticular (SR) Ca2+release events during metabolic acidification were investigated using confocal microscope imaging of Fluo-4-loaded ventricular myocytes. Results: In Langendorff-perfused murine hearts, introduction of lactic acid into the Krebs-Henseleit perfusate resulted in abnormal electrical activity and ventricular tachycardia. The CaMKII inhibitor, KN-93 (2 μm), reversibly suppressed this spontaneous arrhythmogenesis during intrinsic rhythm and regular 8 Hz pacing. However, it failed to suppress arrhythmia evoked by programmed electrical stimulation. These findings paralleled a CaMKII-independent reduction in the transmural repolarization gradients during acidosis, which previously has been associated with the re-entrant substrate under other conditions. Similar acidification produced spontaneous AP firing and membrane potential oscillations in patch-clamped isolated ventricular myocytes when pipette solutions permitted cytosolic Ca2+ to increase following acidification. However, these were abolished by both KN-93 and use of pipette solutions that held cytosolic Ca2+ constant during acidosis. Acidosis also induced spontaneous Ca2+ waves in isolated intact Fluo-4-loaded myocytes studied using confocal microscopy that were abolished by KN-93. Conclusion: These findings together implicate CaMKII-dependent SR Ca2+ waves in spontaneous arrhythmic events during metabolic acidification.
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Affiliation(s)
- T H Pedersen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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152
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Sag CM, Wadsack DP, Khabbazzadeh S, Abesser M, Grefe C, Neumann K, Opiela MK, Backs J, Olson EN, Brown JH, Neef S, Maier SKG, Maier LS. Calcium/calmodulin-dependent protein kinase II contributes to cardiac arrhythmogenesis in heart failure. Circ Heart Fail 2009; 2:664-75. [PMID: 19919992 DOI: 10.1161/circheartfailure.109.865279] [Citation(s) in RCA: 137] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
BACKGROUND Transgenic (TG) Ca/calmodulin-dependent protein kinase II (CaMKII)delta(C) mice have heart failure and isoproterenol (ISO)-inducible arrhythmias. We hypothesized that CaMKII contributes to arrhythmias and underlying cellular events and that inhibition of CaMKII reduces cardiac arrhythmogenesis in vitro and in vivo. METHODS AND RESULTS Under baseline conditions, isolated cardiac myocytes from TG mice showed an increased incidence of early afterdepolarizations compared with wild-type myocytes (P<0.05). CaMKII inhibition (AIP) completely abolished these afterdepolarizations in TG cells (P<0.05). Increasing intracellular Ca stores using ISO (10(-8) M) induced a larger amount of delayed afterdepolarizations and spontaneous action potentials in TG compared with wild-type cells (P<0.05). This seems to be due to an increased sarcoplasmic reticulum (SR) Ca leak because diastolic [Ca](i) rose clearly on ISO in TG but not in wild-type cells (+20+/-5% versus +3+/-4% at 10(-6) M ISO, P<0.05). In parallel, SR Ca leak assessed by spontaneous SR Ca release events showed an increased Ca spark frequency (3.9+/-0.5 versus 2.0+/-0.4 sparks per 100 microm(-1).s(-1), P<0.05). However, CaMKII inhibition (either pharmacologically using KN-93 or genetically using an isoform-specific CaMKIIdelta-knockout mouse model) significantly reduced SR Ca spark frequency, although this rather increased SR Ca content. In parallel, ISO increased the incidence of early (54% versus 4%, P<0.05) and late (86% versus 43%, P<0.05) nonstimulated events in TG versus wild-type myocytes, but CaMKII inhibition (KN-93 and KO) reduced these proarrhythmogenic events (P<0.05). In addition, CaMKII inhibition in TG mice (KN-93) clearly reduced ISO-induced arrhythmias in vivo (P<0.05). CONCLUSIONS We conclude that CaMKII contributes to cardiac arrhythmogenesis in TG CaMKIIdelta(C) mice having heart failure and suggest the increased SR Ca leak as an important mechanism. Moreover, CaMKII inhibition reduces cardiac arrhythmias in vitro and in vivo and may therefore indicate a potential role for future antiarrhythmic therapies warranting further studies.
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Affiliation(s)
- Can M Sag
- Department of Cardiology and Pneumology, Heart Center, Georg-August-University, Göttingen, Germany
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153
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Chelu MG, Sarma S, Sood S, Wang S, van Oort RJ, Skapura DG, Li N, Santonastasi M, Müller FU, Schmitz W, Schotten U, Anderson ME, Valderrábano M, Dobrev D, Wehrens XHT. Calmodulin kinase II-mediated sarcoplasmic reticulum Ca2+ leak promotes atrial fibrillation in mice. J Clin Invest 2009; 119:1940-51. [PMID: 19603549 DOI: 10.1172/jci37059] [Citation(s) in RCA: 212] [Impact Index Per Article: 14.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
A trial fibrillation (AF), the most common human cardiac arrhythmia, is associated with abnormal intracellular Ca2+ handling. Diastolic Ca2+ release from the sarcoplasmic reticulum via "leaky" ryanodine receptors (RyR2s) is hypothesized to contribute to arrhythmogenesis in AF, but the molecular mechanisms are incompletely understood. Here, we have shown that mice with a genetic gain-of-function defect in Ryr2 (which we termed Ryr2R176Q/+ mice) did not exhibit spontaneous AF but that rapid atrial pacing unmasked an increased vulnerability to AF in these mice compared with wild-type mice. Rapid atrial pacing resulted in increased Ca2+/calmodulin-dependent protein kinase II (CaMKII) phosphorylation of RyR2, while both pharmacologic and genetic inhibition of CaMKII prevented AF inducibility in Ryr2R176Q/+ mice. This result suggests that AF requires both an arrhythmogenic substrate (e.g., RyR2 mutation) and enhanced CaMKII activity. Increased CaMKII phosphorylation of RyR2 was observed in atrial biopsies from mice with atrial enlargement and spontaneous AF, goats with lone AF, and patients with chronic AF. Genetic inhibition of CaMKII phosphorylation of RyR2 in Ryr2S2814A knockin mice reduced AF inducibility in a vagotonic AF model. Together, these findings suggest that increased RyR2-dependent Ca2+ leakage due to enhanced CaMKII activity is an important downstream effect of CaMKII in individuals susceptible to AF induction.
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Affiliation(s)
- Mihail G Chelu
- Department of Molecular Physiology and Biophysics, Baylor College of Medicine, Houston, Texas, USA
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154
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Yoo B, Lemaire A, Mangmool S, Wolf MJ, Curcio A, Mao L, Rockman HA. Beta1-adrenergic receptors stimulate cardiac contractility and CaMKII activation in vivo and enhance cardiac dysfunction following myocardial infarction. Am J Physiol Heart Circ Physiol 2009; 297:H1377-86. [PMID: 19633206 DOI: 10.1152/ajpheart.00504.2009] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/19/2023]
Abstract
The beta-adrenergic receptor (betaAR) signaling system is one of the most powerful regulators of cardiac function and a key regulator of Ca(2+) homeostasis. We investigated the role of betaAR stimulation in augmenting cardiac function and its role in the activation of Ca(2+)/calmodulin-dependent kinase II (CaMKII) using various betaAR knockouts (KO) including beta(1)ARKO, beta(2)ARKO, and beta(1)/beta(2)AR double-KO (DKO) mice. We employed a murine model of left anterior descending coronary artery ligation to examine the differential contributions of specific betaAR subtypes in the activation of CaMKII in vivo in failing myocardium. Cardiac inotropy, chronotropy, and CaMKII activity following short-term isoproterenol stimulation were significantly attenuated in beta(1)ARKO and DKO compared with either the beta(2)ARKO or wild-type (WT) mice, indicating that beta(1)ARs are required for catecholamine-induced increases in contractility and CaMKII activity. Eight weeks after myocardial infarction (MI), beta(1)ARKO and DKO mice showed a significant attenuation in fractional shortening compared with either the beta(2)ARKO or WT mice. CaMKII activity after MI was significantly increased only in the beta(2)ARKO and WT hearts and not in the beta(1)ARKO and DKO hearts. The border zone of the infarct in the beta(2)ARKO and WT hearts demonstrated significantly increased apoptosis by TUNEL staining compared with the beta(1)ARKO and DKO hearts. Taken together, these data show that cardiac function and CaMKII activity are mediated almost exclusively by the beta(1)AR. Moreover, it appears that beta(1)AR signaling is detrimental to cardiac function following MI, possibly through activation of CaMKII.
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Affiliation(s)
- ByungSu Yoo
- Departments of Medicine, Cell Biology and Molecular Genetics, Duke University Medical Center, Durham, North Carolina 27710, USA
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155
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Zhang X, Tallini YN, Chen Z, Gan L, Wei B, Doran R, Miao L, Xin HB, Kotlikoff MI, Ji G. Dissociation of FKBP12.6 from ryanodine receptor type 2 is regulated by cyclic ADP-ribose but not beta-adrenergic stimulation in mouse cardiomyocytes. Cardiovasc Res 2009; 84:253-62. [PMID: 19578067 DOI: 10.1093/cvr/cvp212] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
AIMS Beta-adrenergic augmentation of Ca(2+) sparks and cardiac contractility has been functionally linked to phosphorylation-dependent dissociation of FK506 binding protein 12.6 (FKBP12.6) regulatory proteins from ryanodine receptors subtype 2 (RYR2). We used FKBP12.6 null mice to test the extent to which the dissociation of FKBP12.6 affects Ca(2+) sparks and mediates the inotropic action of isoproterenol (ISO), and to investigate the underlying mechanisms of cyclic ADP-ribose (cADPR) regulation of Ca(2+) sparks. METHODS AND RESULTS Ca(2+) sparks and contractility were measured in cardiomyocytes and papillary muscle segments from FKBP12.6 null mice, and western blot analysis was carried out on sarcoplasmic reticulum microsomes prepared from mouse heart. Exposure to ISO resulted in a three- and two-fold increase in Ca(2+) spark frequency in wild-type (WT) and FKBP12.6 knockout (KO) myocytes, respectively, and Ca(2+) spark kinetics were also significantly altered in both types of cells. The effects of ISO on Ca(2+) spark properties in KO cells were inhibited by pre-treatment with thapsigargin or phospholamban inhibitory antibody, 2D12. Moreover, twitch force magnitude and the rate of force development were not significantly different in papillary muscles from WT and KO mice. Unlike beta-adrenergic stimulation, cADPR stimulation increased Ca(2+) spark frequency (2.8-fold) and altered spark kinetics only in WT but not in KO mice. The effect of cADPR on spark properties was not entirely blocked by pre-treatment with thapsigargin or 2D12. In voltage-clamped cells, cADPR increased the peak Ca(2+) of the spark without altering the decay time. We also noticed that basal Ca(2+) spark properties in KO mice were markedly altered compared with those in WT mice. CONCLUSION Our data demonstrate that dissociation of FKBP12.6 from the RYR2 complex does not play a significant role in beta-adrenergic-stimulated Ca(2+) release in heart cells, whereas this mechanism does underlie the action of cADPR.
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Affiliation(s)
- Xu Zhang
- National Laboratory of Biomacromolecules, Institute of Biophysics, Chinese Academy of Sciences, 15 Datun Road, Chaoyang District, Beijing 100101, China
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156
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Kawashima H, Satoh H, Saotome M, Urushida T, Katoh H, Hayashi H. Protein phosphatase inhibitor-1 augments a protein kinase A-dependent increase in the Ca2+ loading of the sarcoplasmic reticulum without changing its Ca2+ release. Circ J 2009; 73:1133-40. [PMID: 19377265 DOI: 10.1253/circj.cj-08-0871] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
BACKGROUND An increase in cytosolic protein phosphatases (PPs) de-phosphorylates phospholamban, decreasing the Ca(2+) uptake of the sarcoplasmic reticulum (SR). The effects of PP inhibitors on cellular Ca(2+) handling were investigated. METHODS AND RESULTS Twitch Ca(2+) transients (CaTs) and cell shortening were measured in intact rat cardiac myocytes, and caffeine-induced Ca(2+) transients (CaffCaTs) and Ca(2+) sparks were studied in saponin-permeabilized cells. Calyculin A augmented isoproterenol-induced increases in CaTs and cell shortening without altering the diastolic [Ca(2+)](i) and twitch [Ca(2+)](i) decay. The protein kinase A catalytic subunit (PKA(cat)) increased the peak of CaffCaTs between 5 and 50 U/ml, and the addition of inhibitor-1 (I-1) augmented the increase. PKA(cat) increased Ca(2+) spark frequency and the addition of I-1 increased it further. PKA(cat) at 50 U/ml amplified the peak and prolonged the duration of Ca(2+) sparks, whereas the addition of I-1 did not alter them. An abrupt inhibition of SR Ca(2+) uptake following exposure to PKA(cat) caused a gradual decrease in Ca(2+) spark frequency, but the addition of I-1 did not accelerate the decline of Ca(2+) spark frequency or CaffCaTs. CONCLUSIONS Inhibition of PPs augmented the inotropic effect of isoproterenol. Specific inhibition of PP1 could stimulate the Ca(2+) uptake of the SR with less significant effects on the Ca(2+) release.
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Affiliation(s)
- Hirotaka Kawashima
- Division of Cardiology, Internal Medicine III, Hamamatsu University School of Medicine, Hamamatsu 431-3192, Japan
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157
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Ling H, Zhang T, Pereira L, Means CK, Cheng H, Gu Y, Dalton ND, Peterson KL, Chen J, Bers D, Brown JH, Heller Brown J. Requirement for Ca2+/calmodulin-dependent kinase II in the transition from pressure overload-induced cardiac hypertrophy to heart failure in mice. J Clin Invest 2009; 119:1230-40. [PMID: 19381018 DOI: 10.1172/jci38022] [Citation(s) in RCA: 300] [Impact Index Per Article: 20.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/11/2008] [Accepted: 02/25/2009] [Indexed: 11/17/2022] Open
Abstract
Ca2+/calmodulin-dependent kinase II (CaMKII) has been implicated in cardiac hypertrophy and heart failure. We generated mice in which the predominant cardiac isoform, CaMKIIdelta, was genetically deleted (KO mice), and found that these mice showed no gross baseline changes in ventricular structure or function. In WT and KO mice, transverse aortic constriction (TAC) induced comparable increases in relative heart weight, cell size, HDAC5 phosphorylation, and hypertrophic gene expression. Strikingly, while KO mice showed preserved hypertrophy after 6-week TAC, CaMKIIdelta deficiency significantly ameliorated phenotypic changes associated with the transition to heart failure, such as chamber dilation, ventricular dysfunction, lung edema, cardiac fibrosis, and apoptosis. The ratio of IP3R2 to ryanodine receptor 2 (RyR2) and the fraction of RyR2 phosphorylated at the CaMKII site increased significantly during development of heart failure in WT mice, but not KO mice, and this was associated with enhanced Ca2+ spark frequency only in WT mice. We suggest that CaMKIIdelta contributes to cardiac decompensation by enhancing RyR2-mediated sarcoplasmic reticulum Ca2+ leak and that attenuating CaMKIIdelta activation can limit the progression to heart failure.
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Affiliation(s)
- Haiyun Ling
- Department of Pharmacology, UCSD, La Jolla, California 92093-0636, USA
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158
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Sigalas C, Bent S, Kitmitto A, O'Neill S, Sitsapesan R. Ca(2+)-calmodulin can activate and inactivate cardiac ryanodine receptors. Br J Pharmacol 2009; 156:794-806. [PMID: 19220289 DOI: 10.1111/j.1476-5381.2008.00092.x] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022] Open
Abstract
BACKGROUND AND PURPOSE Ca(2+)-calmodulin (Ca(2+)CaM) is widely accepted as an inhibitor of cardiac ryanodine receptors (RyR2); however, the effects of physiologically relevant CaM concentrations have not been fully investigated. EXPERIMENTAL APPROACH We investigated the effects of low concentrations of Ca(2+)CaM (50-100 nmol.L(-1)) on the gating of native sheep RyR2, reconstituted into bilayers. Suramin displaces CaM from RyR2 and we have used a gel-shift assay to provide evidence of the mechanism underlying this effect. Finally, using suramin to displace endogenous CaM from RyR2 in permeabilized cardiac cells, we have investigated the effects of 50 nmol.L(-1) CaM on sarcoplasmic reticulum (SR) Ca(2+)-release. KEY RESULTS Ca(2+)CaM activated or inhibited single RyR2, but activation was much more likely at low (50-100 nmol.L(-1)) concentrations. Also, suramin displaced CaM from a peptide of the CaM binding domain of RyR2, indicating that, like the skeletal isoform (RyR1), suramin directly competes with CaM for its binding site on the channel. Pre-treatment of rat permeabilized ventricular myocytes with suramin to displace CaM, followed by addition of 50 nmol x L(-1) CaM to the mock cytoplasmic solution caused an increase in the frequency of spontaneous Ca(2+)-release events. Application of caffeine demonstrated that 50 nmol x L(-1) CaM reduced SR Ca(2+) content. CONCLUSIONS AND IMPLICATIONS We describe for the first time how Ca(2+)CaM is capable, not only of inactivating, but also of activating RyR2 channels in bilayers in a CaM kinase II-independent manner. Similarly, in cardiac cells, CaM stimulates SR Ca(2+)-release and the use of caffeine suggests that this is a RyR2-mediated effect.
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Affiliation(s)
- C Sigalas
- Department of Physiology and Pharmacology and Bristol Heart Institute, University of Bristol, Bristol, UK
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159
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Local control of mitochondrial membrane potential, permeability transition pore and reactive oxygen species by calcium and calmodulin in rat ventricular myocytes. J Mol Cell Cardiol 2009; 46:989-97. [PMID: 19318235 DOI: 10.1016/j.yjmcc.2008.12.022] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/04/2008] [Revised: 12/24/2008] [Accepted: 12/30/2008] [Indexed: 11/21/2022]
Abstract
Calmodulin (CaM) and Ca(2+)/CaM-dependent protein kinase II (CaMKII) play important roles in the development of heart failure. In this study, we evaluated the effects of CaM on mitochondrial membrane potential (DeltaPsi(m)), permeability transition pore (mPTP) and the production of reactive oxygen species (ROS) in permeabilized myocytes; our findings are as follows. (1) CaM depolarized DeltaPsi(m) dose-dependently, but this was prevented by an inhibitor of CaM (W-7) or CaMKII (autocamtide 2-related inhibitory peptide (AIP)). (2) CaM accelerated calcein leakage from mitochondria, indicating the opening of mPTP, however this was prevented by AIP. (3) Cyclosporin A (an inhibitor of the mPTP) inhibited both CaM-induced DeltaPsi(m) depolarization and calcein leakage. (4) CaM increased mitochondrial ROS, which was related to DeltaPsi(m) depolarization and the opening of mPTP. (5) Chelating of cytosolic Ca(2+) by BAPTA, the depletion of SR Ca(2+) by thapsigargin (an inhibitor of SERCA) and the inhibition of mitochondrial Ca(2+) uniporter by Ru360 attenuated the effects of CaM on mitochondrial function. (6) CaM accelerated Ca(2+) extrusion from mitochondria. We conclude that CaM/CaMKII depolarized DeltaPsi(m) and opened mPTP by increasing ROS production, and these effects were strictly regulated by the local increase in cytosolic Ca(2+) concentration, initiated by Ca(2+) releases from the SR. In addition, CaM was involved in the regulation of mitochondrial Ca(2+) homeostasis.
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160
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Shao CH, Wehrens XHT, Wyatt TA, Parbhu S, Rozanski GJ, Patel KP, Bidasee KR. Exercise training during diabetes attenuates cardiac ryanodine receptor dysregulation. J Appl Physiol (1985) 2009; 106:1280-92. [PMID: 19131475 DOI: 10.1152/japplphysiol.91280.2008] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The present study was undertaken to assess the effects of exercise training (ExT) initiated after the onset of diabetes on cardiac ryanodine receptor expression and function. Type 1 diabetes was induced in male Sprague-Dawley rats using streptozotocin (STZ). Three weeks after STZ injection, diabetic rats were divided into two groups. One group underwent ExT for 4 wk while the other group remained sedentary. After 7 wk of sedentary diabetes, cardiac fractional shortening, rate of rise of left ventricular pressure, and myocyte contractile velocity were reduced by 14, 36, 44%, respectively. Spontaneous Ca(2+) spark frequency increased threefold, and evoked Ca(2+) release was dyssynchronous with diastolic Ca(2+) releases. Steady-state type 2 ryanodine receptor (RyR2) protein did not change, but its response to Ca(2+) was altered. RyR2 also exhibited 1.8- and 1.5-fold increases in phosphorylation at Ser(2808) and Ser(2814). PKA activity was reduced by 75%, but CaMKII activity was increased by 50%. Four weeks of ExT initiated 3 wk after the onset of diabetes blunted decreases in cardiac fractional shortening and rate of left ventricular pressure development, increased the responsiveness of the myocardium to isoproterenol stimulation, attenuated the increase in Ca(2+) spark frequency, and minimized dyssynchronous and diastolic Ca(2+) releases. ExT also normalized the responsiveness of RyR2 to Ca(2+) activation, attenuated increases in RyR2 phosphorylation at Ser(2808) and Ser(2814), and normalized CaMKII and PKA activities. These data are the first to show that ExT during diabetes normalizes RyR2 function and Ca(2+) release from the sarcoplasmic reticulum, providing insights into mechanisms by which ExT during diabetes improves cardiac function.
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Affiliation(s)
- Chun-Hong Shao
- Department of Pharmacology and Experimental Neuroscience, University of Nebraska Medical Center, Omaha, NE, USA
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161
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Katz G, Arad M, Eldar M. Catecholaminergic polymorphic ventricular tachycardia from bedside to bench and beyond. Curr Probl Cardiol 2009; 34:9-43. [PMID: 19068246 DOI: 10.1016/j.cpcardiol.2008.09.002] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Catecholaminergic polymorphic ventricular tachycardia (CPVT) is a primary electrical myocardial disease characterized by exercise- and stress-related ventricular tachycardia manifested as syncope and sudden death. The disease has a heterogeneous genetic basis, with mutations in the cardiac Ryanodine Receptor channel (RyR2) gene accounting for an autosomal-dominant form (CPVT1) in approximately 50% and mutations in the cardiac calsequestrin gene (CASQ2) accounting for an autosomal-recessive form (CPVT2) in up to 2% of CPVT cases. Both RyR2 and calsequestrin are important participants in the cardiac cellular calcium homeostasis. We review the physiology of the cardiac calcium homeostasis, including the cardiac excitation contraction coupling and myocyte calcium cycling. The pathophysiology of cardiac arrhythmias related to myocyte calcium handling and the effects of different modulators are discussed. The putative derangements in myocyte calcium homeostasis responsible for CPVT, as well as the clinical manifestations and therapeutic options available, are described.
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162
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Xie LH, Chen F, Karagueuzian HS, Weiss JN. Oxidative-stress-induced afterdepolarizations and calmodulin kinase II signaling. Circ Res 2008; 104:79-86. [PMID: 19038865 DOI: 10.1161/circresaha.108.183475] [Citation(s) in RCA: 218] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
In the heart, oxidative stress caused by exogenous H(2)O(2) has been shown to induce early afterdepolarizations (EADs) and triggered activity by impairing Na current (I(Na)) inactivation. Because H(2)O(2) activates Ca(2+)/calmodulin kinase (CaMK)II, which also impairs I(Na) inactivation and promotes EADs, we hypothesized that CaMKII activation may be an important factor in EADs caused by oxidative stress. Using the patch-clamp and intracellular Ca (Ca(i)) imaging in Fluo-4 AM-loaded rabbit ventricular myocytes, we found that exposure to H(2)O(2) (0.2 to 1 mmol/L) for 5 to 15 minutes consistently induced EADs that were suppressed by the I(Na) blocker tetrodotoxin (10 micromol/L), as well as the I(Ca,L) blocker nifedipine. H(2)O(2) enhanced both peak and late I(Ca,L), consistent with CaMKII-mediated facilitation. By prolonging the action potential plateau and increasing Ca influx via I(Ca,L), H(2)O(2)-induced EADs were also frequently followed by DADs in response to spontaneous (ie, non-I(Ca,L)-gated) sarcoplasmic reticulum Ca release after repolarization. The CaMKII inhibitor KN-93 (1 micromol/L; n=4), but not its inactive analog KN-92 (1 micromol/L, n=5), prevented H(2)O(2)-induced EADs and DADs, and the selective CaMKII peptide inhibitor AIP (autocamtide-2-related inhibitory peptide) (2 micromol/L) significantly delayed their onset. In conclusion, H(2)O(2)-induced afterdepolarizations depend on both impaired I(Na) inactivation to reduce repolarization reserve and enhancement of I(Ca,L) to reverse repolarization, which are both facilitated by CaMKII activation. Our observations support a link between increased oxidative stress, CaMKII activation, and afterdepolarizations as triggers of lethal ventricular arrhythmias in diseased hearts.
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Affiliation(s)
- Lai-Hua Xie
- Department of Cell Biology and Molecular Medicine, University of Medicine and Dentistry, New Jersey-New Jersey Medical School, Newark, USA
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163
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Liu QH, Zheng YM, Korde AS, Li XQ, Ma J, Takeshima H, Wang YX. Protein kinase C-epsilon regulates local calcium signaling in airway smooth muscle cells. Am J Respir Cell Mol Biol 2008; 40:663-71. [PMID: 19011160 DOI: 10.1165/rcmb.2008-0323oc] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022] Open
Abstract
Protein kinase C (PKC) is known to regulate ryanodine receptor (RyR)-mediated local Ca(2+) signaling (Ca(2+) spark) in airway and vascular smooth muscle cells (SMCs), but its specific molecular mechanisms and functions still remain elusive. In this study, we reveal that, in airway SMCs, specific PKCepsilon peptide inhibitor and gene deletion significantly increased the frequency of Ca(2+) sparks, and decreased the amplitude of Ca(2+) sparks in the presence of xestospogin-C to eliminate functional inositol 1,4,5-triphosphate receptors. PKCepsilon activation with phorbol-12-myristate-13-acetate significantly decreased Ca(2+) spark frequency and increased Ca(2+) spark amplitude. The effect of PKCepsilon inhibition or activation on Ca(2+) sparks was completely lost in PKCepsilon(-/-) cells. PKCepsilon inhibition or PKCepsilon activation was unable to affect Ca(2+) sparks in RyR1(-/-) and RyR1(+/-) cells. Modification of RyR2 activity by FK506-binding protein 12.6 homozygous or RyR2 heterozygous gene deletion did not prevent the effect of PKCepsilon inhibition or activation. RyR3 homogenous gene deletion did not block the effect of PKCepsilon inhibition and activation, either. PKCepsilon inhibition promotes agonist-induced airway muscle contraction, whereas PKCepsilon activation produces an opposite effect. Taken together, these results indicate that PKCepsilon regulates Ca(2+) sparks by specifically interacting with RyR1, which plays an important role in the control of contractile responses in airway SMCs.
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Affiliation(s)
- Qing-Hua Liu
- Center for Cardiovascular Sciences, Albany Medical College, Albany, New York 12208, USA
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164
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Thiel WH, Chen B, Hund TJ, Koval OM, Purohit A, Song LS, Mohler PJ, Anderson ME. Proarrhythmic defects in Timothy syndrome require calmodulin kinase II. Circulation 2008; 118:2225-34. [PMID: 19001023 DOI: 10.1161/circulationaha.108.788067] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
BACKGROUND Timothy syndrome (TS) is a disease of excessive cellular Ca(2+) entry and life-threatening arrhythmias caused by a mutation in the primary cardiac L-type Ca(2+) channel (Ca(V)1.2). The TS mutation causes loss of normal voltage-dependent inactivation of Ca(V)1.2 current (I(Ca)). During cellular Ca(2+) overload, the calmodulin-dependent protein kinase II (CaMKII) causes arrhythmias. We hypothesized that CaMKII is a part of the proarrhythmic mechanism in TS. METHODS AND RESULTS We developed an adult rat ventricular myocyte model of TS (G406R) by lentivirus-mediated transfer of wild-type and TS Ca(V)1.2. The exogenous Ca(V)1.2 contained a mutation (T1066Y) conferring dihydropyridine resistance, so we could silence endogenous Ca(V)1.2 with nifedipine and maintain peak I(Ca) at control levels in infected cells. TS Ca(V)1.2-infected ventricular myocytes exhibited the signature voltage-dependent inactivation loss under Ca(2+) buffering conditions, not permissive for CaMKII activation. In physiological Ca(2+) solutions, TS Ca(V)1.2-expressing ventricular myocytes exhibited increased CaMKII activity and a proarrhythmic phenotype that included action potential prolongation, increased I(Ca) facilitation, and afterdepolarizations. Intracellular dialysis of a CaMKII inhibitory peptide, but not a control peptide, reversed increases in I(Ca) facilitation, normalized the action potential, and prevented afterdepolarizations. We developed a revised mathematical model that accounts for CaMKII-dependent and CaMKII-independent effects of the TS mutation. CONCLUSIONS In TS, the loss of voltage-dependent inactivation is an upstream initiating event for arrhythmia phenotypes that are ultimately dependent on CaMKII activation.
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165
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Jin H, Lyon AR, Akar FG. Arrhythmia mechanisms in the failing heart. PACING AND CLINICAL ELECTROPHYSIOLOGY: PACE 2008; 31:1048-56. [PMID: 18684263 DOI: 10.1111/j.1540-8159.2008.01134.x] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
BACKGROUND Heart failure (HF) claims over 200,000 lives annually in the United States alone. Approximately 50% of these deaths are sudden and unexpected, and presumably the consequence of lethal ventricular tachyarrhythmias. Electrical remodeling that occurs at the cellular and tissue network levels predisposes patients with HF to malignant arrhythmias. Our limited understanding of fundamental arrhythmia mechanisms has hampered the development of effective treatment strategies for these patients. METHODS AND CONCLUSIONS In this review, we outline recent advances in our understanding of arrhythmia mechanisms in the failing heart, highlighting various aspects of remodeling of ion channels, calcium handling proteins, and gap junction-related molecules. As will be discussed, these changes promote the prolongation of the action potential, the enhancement of spatio-temporal gradients of repolarization, the formation of calcium-mediated triggers and conduction abnormalities, all of which combine to form an electrophysiological substrate that is ripe for the genesis of lethal arrhythmias and sudden cardiac death.
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Affiliation(s)
- Hongwei Jin
- Division of Cardiology, Cardiovascular Research Center, Department of Pharmacology and Systems Therapeutics, Mount Sinai School of Medicine, New York, New York, USA
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166
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Shirokova N, Niggli E. Studies of RyR function in situ. Methods 2008; 46:183-93. [PMID: 18848990 DOI: 10.1016/j.ymeth.2008.09.017] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/10/2008] [Accepted: 09/12/2008] [Indexed: 10/21/2022] Open
Abstract
The ryanodine receptors (RyRs) are intracellular Ca2+ release channels of the sarcoplasmic reticulum (SR) involved in many cellular responses, including muscle excitation-contraction coupling. Multiple biochemical and biophysical methods are available to study RyR functions. However, most of them are somewhat limited because they can only be used to examine channels which are purified from the SR and no longer in their natural environment. In this review we discuss optical methods for studying RyR functions in situ. We describe several techniques for the investigation of local (microscopic) intracellular Ca2+ signals (a.k.a Ca2+ sparks) by means of confocal microscopy and flash photolysis of caged compounds. We discuss how these studies can and will continue to contribute to our understanding of RyR function in physiological and pathological conditions.
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Affiliation(s)
- Natalia Shirokova
- Department of Pharmacology & Physiology, UMDNJ-New Jersey Medical School, 185 South Orange Avenue, Newark, NJ 07103, USA.
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167
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Gillespie D, Fill M. Intracellular calcium release channels mediate their own countercurrent: the ryanodine receptor case study. Biophys J 2008; 95:3706-14. [PMID: 18621826 PMCID: PMC2553138 DOI: 10.1529/biophysj.108.131987] [Citation(s) in RCA: 90] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Accepted: 07/01/2008] [Indexed: 01/09/2023] Open
Abstract
Intracellular calcium release channels like ryanodine receptors (RyRs) and inositol trisphosphate receptors (IP(3)Rs) mediate large Ca(2+) release events from Ca(2+) storage organelles lasting >5 ms. To have such long-lasting Ca(2+) efflux, a countercurrent of other ions is necessary to prevent the membrane potential from becoming the Ca(2+) Nernst potential in <1 ms. A recent model of ion permeation through a single, open RyR channel is used here to show that the vast majority of this countercurrent is conducted by the RyR itself. Consequently, changes in membrane potential are minimized locally and instantly, assuring maintenance of a Ca(2+)-driving force. This RyR autocountercurrent is possible because of the poor Ca(2+) selectivity and high conductance for both monovalent and divalent cations of these channels. The model shows that, under physiological conditions, the autocountercurrent clamps the membrane potential near 0 mV within approximately 150 mus. Consistent with experiments, the model shows how RyR unit Ca(2+) current is defined by luminal [Ca(2+)], permeable ion composition and concentration, and pore selectivity and conductance. This very likely is true of the highly homologous pore of the IP(3)R channel.
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Affiliation(s)
- Dirk Gillespie
- Department of Molecular Biophysics and Physiology, Rush University Medical Center, Chicago, Illinois, USA.
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168
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Yano M, Yamamoto T, Kobayashi S, Ikeda Y, Matsuzaki M. Defective Ca2+ cycling as a key pathogenic mechanism of heart failure. Circ J 2008; 72 Suppl A:A22-30. [PMID: 18772523 DOI: 10.1253/circj.cj-08-0070] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Structural and functional alterations in the Ca(2+) regulatory proteins present in the sarcoplasmic reticulum (SR) have recently been shown to play a crucial role in the pathogenesis of heart failure (HF), and lethal arrhythmia as well. Chronic activation of the sympathetic nervous system induces abnormalities in both the function and structure of these proteins. For instance, the diastolic Ca(2+) leak through the SR Ca(2+) release channel (ryanodine receptor) reduces the SR Ca(2+) content, inducing contractile dysfunction. Moreover, the Ca(2+) leak provides a substrate for delayed after depolarization that leads to lethal arrhythmia. There is a considerable body of evidence regarding the role of Ca(2+) cycling abnormality in HF.
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Affiliation(s)
- Masafumi Yano
- Department of Medicine and Clinical Science, Division of Cardiology, Yamaguchi University Graduate School of Medicine, Ube, Japan.
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169
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Abstract
Abnormal intracellular Ca(2+) handling by the sarcoplasmic reticulum (SR) is a critical factor in the development of heart failure (HF). Not only decreased Ca(2+) uptake, but also uncoordinated Ca(2+) release plays a significant role in contractile and relaxation dysfunction. Spontaneous Ca(2+) release through ryanodine receptor (RyR) 2, a huge tetrameric protein, during diastole leads to a decrease in the SR Ca(2+) content, and also triggers delayed after depolarization that is a substrate for lethal arrhythmia. Several disease-linked mutations of RyR have been reported in patients with catecholaminergic polymorphic ventricular tachycardia (CPVT) or arrhythmogenic right ventricular cardiomyopathy type 2 (ARVC2). The unique distribution of these mutation sites has lead to the concept that an interaction among the putative regulatory domains within RyR may play a key role in regulating channel opening, and that there seems to be a common abnormality in the channel disorder of HF and CPVT/ARVC2. Recent knowledge gained from pathological conditions may lead to the development of a new therapeutic strategy for the treatment of HF or cardiac arrhythmia.
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Affiliation(s)
- Masafumi Yano
- Department of Medicine and Clinical Science, Division of Cardiology, Yamaguchi University Graduate School of Medicine, 1-1-1 Minamikogushi, Ube 755-8505, Japan.
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170
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Valdivia HH, Houser SR. Response to Mattiazzi et al:. Circ Res 2008. [DOI: 10.1161/circresaha.108.179614] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Affiliation(s)
- Héctor H. Valdivia
- Department of Physiology, University of Wisconsin Medical School, Madison, WI
| | - Steven R. Houser
- Department of Physiology, Cardiovascular Research Center, Temple University School of Medicine, Philadelphia, Pa,
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171
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Yeh YH, Wakili R, Qi XY, Chartier D, Boknik P, Kääb S, Ravens U, Coutu P, Dobrev D, Nattel S. Calcium-Handling Abnormalities Underlying Atrial Arrhythmogenesis and Contractile Dysfunction in Dogs With Congestive Heart Failure. Circ Arrhythm Electrophysiol 2008; 1:93-102. [DOI: 10.1161/circep.107.754788] [Citation(s) in RCA: 217] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Background—
Congestive heart failure (CHF) is a common cause of atrial fibrillation. Focal sources of unknown mechanism have been described in CHF-related atrial fibrillation. The authors hypothesized that abnormal calcium (Ca
2+
) handling contributes to the CHF-related atrial arrhythmogenic substrate.
Methods and Results—
CHF was induced in dogs by ventricular tachypacing (240 bpm �2 weeks). Cellular Ca
2+
-handling properties and expression/phosphorylation status of key Ca
2+
handling and myofilament proteins were assessed in control and CHF atria. CHF decreased cell shortening but increased left atrial diastolic intracellular Ca
2+
concentration ([Ca
2+
]
i
), [Ca
2+
]
i
transient amplitude, and sarcoplasmic reticulum (SR) Ca
2+
load (caffeine-induced [Ca
2+
]
i
release). SR Ca
2+
overload was associated with spontaneous Ca
2+
transient events and triggered ectopic activity, which was suppressed by the inhibition of SR Ca
2+
release (ryanodine) or Na
+
/Ca
2+
exchange. Mechanisms underlying abnormal SR Ca
2+
handling were then studied. CHF increased atrial action potential duration and action potential voltage clamp showed that CHF-like action potentials enhance Ca
2+
i
loading. CHF increased calmodulin-dependent protein kinase II phosphorylation of phospholamban by 120%, potentially enhancing SR Ca
2+
uptake by reducing phospholamban inhibition of SR Ca
2+
ATPase, but it did not affect phosphorylation of SR Ca
2+
-release channels (RyR2). Total RyR2 and calsequestrin (main SR Ca
2+
-binding protein) expression were significantly reduced, by 65% and 15%, potentially contributing to SR dysfunction. CHF decreased expression of total and protein kinase A–phosphorylated myosin-binding protein C (a key contractile filament regulator) by 27% and 74%, potentially accounting for decreased contractility despite increased Ca
2+
transients. Complex phosphorylation changes were explained by enhanced calmodulin-dependent protein kinase IIδ expression and function and type-1 protein-phosphatase activity but downregulated regulatory protein kinase A subunits.
Conclusions—
CHF causes profound changes in Ca
2+
-handling and -regulatory proteins that produce atrial fibrillation–promoting atrial cardiomyocyte Ca
2+
-handling abnormalities, arrhythmogenic triggered activity, and contractile dysfunction.
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Affiliation(s)
- Yung-Hsin Yeh
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Reza Wakili
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Xiao-Yan Qi
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Denis Chartier
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Peter Boknik
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Stefan Kääb
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Ursula Ravens
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Pierre Coutu
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Dobromir Dobrev
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
| | - Stanley Nattel
- From the Department of Medicine and Research Center, Montreal Heart Institute and Université de Montréal (Y.H.Y., R.W., X.Q., D.C., P.C., S.N.), Montreal, Canada; the Department of Pharmacology and Toxicology (R.W., U.R., D.D.), Dresden University of Technology, Dresden, Germany; Chang Gung Memorial Hospital and Chang Gung University (Y.H.Y.), Tao-Yuan, Taiwan; the Department of Pharmacology and Toxicology (P.B.), University of Münster, Münster, Germany; and Ludwig-Maximilians University,
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172
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Abstract
Calcium (Ca) is a universal intracellular second messenger. In muscle, Ca is best known for its role in contractile activation. However, in recent years the critical role of Ca in other myocyte processes has become increasingly clear. This review focuses on Ca signaling in cardiac myocytes as pertaining to electrophysiology (including action potentials and arrhythmias), excitation-contraction coupling, modulation of contractile function, energy supply-demand balance (including mitochondrial function), cell death, and transcription regulation. Importantly, although such diverse Ca-dependent regulations occur simultaneously in a cell, the cell can distinguish distinct signals by local Ca or protein complexes and differential Ca signal integration.
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Affiliation(s)
- Donald M Bers
- Department of Physiology and Cardiovascular Institute, Stritch School of Medicine, Loyola University Chicago, Maywood, IL 60153, USA.
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173
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Ikeda Y, Hoshijima M, Chien KR. Toward biologically targeted therapy of calcium cycling defects in heart failure. Physiology (Bethesda) 2008; 23:6-16. [PMID: 18268360 DOI: 10.1152/physiol.00033.2007] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
A growing body of evidence indicates that heart failure progression is tightly associated with dysregulation of phosphorylation of Ca2+ regulators localized in the sub-cellular microdomain of the sarcoplasmic reticulum. Chemical or genetic correction of abnormalities in cardiac phosphorylation cascades is emerging as a potential target in the treatment of heart failure. Here, we review how specific kinases and phosphatases finely tune Ca2+ cycling and regulate excitation-contraction (E-C) coupling in cardiomyocytes.
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Affiliation(s)
- Yasuhiro Ikeda
- Department of Molecular Cardiovascular Biology, Yamaguchi University School of Medicine, Ube, Japan.
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174
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Stewart R, Song L, Carter SM, Sigalas C, Zaccai NR, Kanamarlapudi V, Bhat MB, Takeshima H, Sitsapesan R. Single-channel characterization of the rabbit recombinant RyR2 reveals a novel inactivation property of physiological concentrations of ATP. J Membr Biol 2008; 222:65-77. [PMID: 18418540 DOI: 10.1007/s00232-008-9102-z] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2008] [Accepted: 03/05/2008] [Indexed: 10/22/2022]
Abstract
Ryanodine receptor 2 (RyR2) cDNA has been available for more than 15 years; however, due to the complex nature of ligand gating in this channel, many aspects of recombinant RyR2 function have been unresearched. We established a stable, inducible HEK 293 cell line expressing full-length rabbit RyR2 cDNA and assessed the single-channel properties of the recombinant RyR2, with particular reference to ligand regulation with Ca2+ as the permeant ion. We found that the single-channel conductances of recombinant RyR2 and RyR2 isolated from cardiac muscle are essentially identical, as is irreversible modification by ryanodine. Although it is known that RyR2 expressed in HEK 293 cells is not associated with FKBP12.6, we demonstrate that these channels do not exhibit any discernable disorganized gating characteristics or subconductance states. We also show that the gating of recombinant RyR2 is indistinguishable from that of channels isolated from cardiac muscle when activated by cytosolic Ca2+, caffeine or suramin. The mechanisms underlying ATP activation are also similar; however, the experiments highlighted a novel effect of ATP at physiologically relevant concentrations of 5-10 mM. With Ca2+ as permeant ion, 5-10 mM ATP consistently inactivated recombinant channels (15/16 experiments). Such inactivation was rarely observed with native RyR2 isolated from cardiac muscle (1 in 16 experiments). However, if the channels were purified, inactivation by ATP was then revealed in all experiments. This action of ATP may be relevant for inactivation of sarcoplasmic reticulum Ca2+ release during cardiac excitation-contraction coupling or may represent unnatural behavior that is revealed when RyR2 is purified or expressed in noncardiac systems.
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Affiliation(s)
- Richard Stewart
- Department of Physiology and Pharmacology, School of Medical Sciences, University of Bristol, University Walk, Bristol, BS8 1TD, UK
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175
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Gellen B, Fernández-Velasco M, Briec F, Vinet L, LeQuang K, Rouet-Benzineb P, Bénitah JP, Pezet M, Palais G, Pellegrin N, Zhang A, Perrier R, Escoubet B, Marniquet X, Richard S, Jaisser F, Gómez AM, Charpentier F, Mercadier JJ. Conditional FKBP12.6 overexpression in mouse cardiac myocytes prevents triggered ventricular tachycardia through specific alterations in excitation-contraction coupling. Circulation 2008; 117:1778-86. [PMID: 18378612 DOI: 10.1161/circulationaha.107.731893] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
BACKGROUND Ca(2+) release from the sarcoplasmic reticulum via the ryanodine receptor (RyR2) activates cardiac myocyte contraction. An important regulator of RyR2 function is FKBP12.6, which stabilizes RyR2 in the closed state during diastole. Beta-adrenergic stimulation has been suggested to dissociate FKBP12.6 from RyR2, leading to diastolic sarcoplasmic reticulum Ca(2+) leakage and ventricular tachycardia (VT). We tested the hypothesis that FKBP12.6 overexpression in cardiac myocytes can reduce susceptibility to VT in stress conditions. METHODS AND RESULTS We developed a mouse model with conditional cardiac-specific overexpression of FKBP12.6. Transgenic mouse hearts showed a marked increase in FKBP12.6 binding to RyR2 compared with controls both at baseline and on isoproterenol stimulation (0.2 mg/kg i.p.). After pretreatment with isoproterenol, burst pacing induced VT in 10 of 23 control mice but in only 1 of 14 transgenic mice (P<0.05). In isolated transgenic myocytes, Ca(2+) spark frequency was reduced by 50% (P<0.01), a reduction that persisted under isoproterenol stimulation, whereas the sarcoplasmic reticulum Ca(2+) load remained unchanged. In parallel, peak I(Ca,L) density decreased by 15% (P<0.01), and the Ca(2+) transient peak amplitude decreased by 30% (P<0.001). A 33.5% prolongation of the caffeine-evoked Ca(2+) transient decay was associated with an 18% reduction in the Na(+)-Ca(2+) exchanger protein level (P<0.05). CONCLUSIONS Increased FKBP12.6 binding to RyR2 prevents triggered VT in normal hearts in stress conditions, probably by reducing diastolic sarcoplasmic reticulum Ca(2+) leak. This indicates that the FKBP12.6-RyR2 complex is an important candidate target for pharmacological prevention of VT.
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176
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Abstract
Diastolic dysfunction is characterized by prolonged relaxation, increased filling pressure, decreased contraction velocity, and reduced cardiac output. Phenotypical features of diastolic dysfunction can be observed at the level of the isolated myocyte. This article reviews the cellular mechanisms that control relaxation at the level of the myocyte in the healthy situation and discusses the alterations that can affect physiologic function during disease. It focuses specifically on the mechanisms that regulate intracellular calcium handling, and the response of the myofilaments to calcium, including the changes in these components that can contribute to diastolic dysfunction.
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Affiliation(s)
- Muthu Periasamy
- Davis Heart and Lung Research Institute, The Ohio State University, Columbus OH, USA.
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177
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Neef S, Maier LS. Remodeling of excitation-contraction coupling in the heart: Inhibition of sarcoplasmic reticulum Ca2+ leak as a novel therapeutic approach. Curr Heart Fail Rep 2008; 4:11-7. [PMID: 17386180 DOI: 10.1007/s11897-007-0020-7] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
In the heart, excitation-contraction coupling is the central mechanism by which electrical activation is translated into cardiac contraction. In heart failure, several proteins involved in this finely concerted regulation are changed with respect to expression, phosphorylation status, and function leading to remodeling of excitation-contraction coupling. The present review article summarizes well known alterations in heart failure and focuses on recent findings especially regarding altered sarcoplasmic reticulum Ca(2+) release process due to two distinct kinases, namely protein kinase A and Ca(2+)/calmodulin-dependent kinase II. Furthermore, it highlights the translation of those findings into possible novel therapeutic approaches.
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Affiliation(s)
- Stefan Neef
- Abteilung Kardiologie und Pneumologie/Herzzentrum, Georg-August-Universität Göttingen, Robert-Koch-Str. 40, 37075 Göttingen, Germany
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178
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Laurita KR, Rosenbaum DS. Cellular mechanisms of arrhythmogenic cardiac alternans. PROGRESS IN BIOPHYSICS AND MOLECULAR BIOLOGY 2008; 97:332-47. [PMID: 18395246 DOI: 10.1016/j.pbiomolbio.2008.02.014] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/22/2022]
Abstract
Despite the strong association between mechanical dysfunction of the heart and sudden death due to arrhythmias, the causal relationship is not well understood. Cardiac alternans has been linked to arrhythmogenesis and can be mediated by intracellular calcium handling. Given the integral role intracellular calcium plays in contractile function, calcium-mediated alternans may represent an important mechanistic link between mechanical dysfunction and electrical instability. This relationship, however, is not well understood due to complex feedback between membrane currents, intracellular calcium, and contraction. This manuscript describes the cellular mechanisms of cardiac alternans. Through several pathways, calcium transient alternans is coupled to repolarization alternans that can form a substrate for reentrant excitation. Abnormal intracellular calcium cycling, either impaired release or impaired reuptake of sarcoplasmic reticulum calcium, is a cellular mechanism of calcium transient alternans. Thus, cardiac alternans is an important mechanistic link between mechanical dysfunction and sudden cardiac death.
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Affiliation(s)
- Kenneth R Laurita
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, Cleveland, OH, USA.
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179
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George CH, Barberini-Jammaers SR, Muller CT. Refocussing therapeutic strategies for cardiac arrhythmias: defining viable molecular targets to restore cardiac ion flux. Expert Opin Ther Pat 2008. [DOI: 10.1517/13543776.18.1.1] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
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180
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Seidler T, Hasenfuss G, Maier LS. Targeting altered calcium physiology in the heart: translational approaches to excitation, contraction, and transcription. Physiology (Bethesda) 2008; 22:328-34. [PMID: 17928546 DOI: 10.1152/physiol.00015.2007] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
Calcium (Ca) is essential for excitation-contraction coupling. At the same time, Ca is of pivotal importance as a second messenger in cardiac signal transduction, where it regulates cardiac growth and function by activation of kinases and phosphatases, ultimately driving transcriptional responses and feeding back on Ca handling proteins, a phenomenon termed excitation-transcription coupling. Cardiac Ca homeostasis thus needs to be maintained via a delicate interplay of proteins to allow physiological function and adaptation, whereas disturbed Ca-handling and Ca-dependent signaling are hallmarks of heart failure. In this review, we will discuss the most recent mechanistic findings in Ca-handling and Ca-signaling proteins in the development of cardiac pathology with a focus on translational aspects.
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Affiliation(s)
- Tim Seidler
- Department of Cardiology and Pneumology, Heart Center Georg-August-University Göttingen, Göttingen, Germany
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181
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182
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Partial inhibition of sarcoplasmic reticulum ca release evokes long-lasting ca release events in ventricular myocytes: role of luminal ca in termination of ca release. Biophys J 2007; 94:1867-79. [PMID: 18024505 DOI: 10.1529/biophysj.107.114694] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
In cardiac myocytes, local sarcoplasmic reticulum (SR) Ca depletion during Ca sparks is believed to play an important role in the termination of SR Ca release. We tested whether decreasing the rate of SR Ca depletion by partially inhibiting SR Ca release channels (ryanodine receptors) delays Ca spark termination. In permeabilized cat ventricular myocytes, 0.7 mM tetracaine caused almost complete Ca spark inhibition followed by a recovery significantly below control level. The recovery was associated with increased SR Ca load and increased Ca spark duration. Additionally, SR Ca release events lasting several hundred milliseconds occurred consistently. These events had a significantly lower initial Ca release flux followed by a stable plateau, indicating delayed release termination and maintained SR Ca load. Increasing SR Ca load (without inhibiting SR Ca release rate) or decreasing SR Ca release rate (without increasing SR Ca load) both induced only a small increase in spark duration. These results show that the combination of decreased release flux and increased SR Ca load has synergistic effects and exerts major changes on the termination of Ca release events. Long-lasting Ca release events may originate from highly interconnected release junctions where Ca diffusion from neighboring sites partially compensates Ca depletion, thereby delaying SR Ca-dependent termination. Eventually, these events terminate by luminal Ca-independent mechanisms, such as inactivation, adaptation, or stochastic attrition.
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183
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Ryanodine receptor mutations in arrhythmias: advances in understanding the mechanisms of channel dysfunction. Biochem Soc Trans 2007; 35:946-51. [DOI: 10.1042/bst0350946] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The cardiac ryanodine receptor (RyR2) mediates rapid Ca2+ efflux from intracellular stores to effect myocyte contraction during the process of EC (excitation–contraction) coupling. It is now known that mutations in this channel perturb Ca2+ release function, leading to triggered arrhythmias that may cause SCD (sudden cardiac death). Resolving the precise molecular mechanisms by which SCD-linked RyR2 dysfunction occurs currently constitutes a burgeoning area of cardiac research. So far, defective channel phosphorylation, accessory protein binding, luminal/cytosolic Ca2+ sensing, and the disruption of interdomain interactions represent the main candidate mechanisms for explaining aberrant SR (sarcoplasmic reticulum) Ca2+ release via mutants of RyR2. It appears increasingly unlikely that a single exclusive common mechanism underlies every case of mutant channel dysfunction, and that each of these potential mechanisms may contribute to the resultant phenotype. The present review will consider very recent mechanistic developments in this field, including new observations from mutant RyR2 transgenic mouse models, peptide-probe studies, and the implications of functional and phenotypic heterogeneity of RyR2 mutations and polymorphisms.
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184
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Laurita KR, Rosenbaum DS. Mechanisms and potential therapeutic targets for ventricular arrhythmias associated with impaired cardiac calcium cycling. J Mol Cell Cardiol 2007; 44:31-43. [PMID: 18061204 DOI: 10.1016/j.yjmcc.2007.10.012] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/02/2007] [Revised: 10/11/2007] [Accepted: 10/16/2007] [Indexed: 11/30/2022]
Abstract
The close relationship between life-threatening ventricular arrhythmias and contractile dysfunction in the heart implicates intracellular calcium cycling as an important underlying mechanism of arrhythmogenesis. Despite this close association, however, the mechanisms of arrhythmogenesis attributable to impaired calcium cycling are not fully appreciated or understood. In this report we review some of the current thinking regarding arrhythmia mechanisms associated with either abnormal impulse initiation (i.e. arrhythmia triggers) or impulse propagation (i.e. arrhythmia substrates). In all cases, the mechanisms are primarily related to dysfunction of calcium regulatory proteins associated with the sarcomere. These findings highlight the broad scope of arrhythmias associated with abnormal calcium cycling, and provide a basis for a causal relationship between cardiac electrical instability and contractile dysfunction. Moreover, calcium cycling proteins may provide much needed targets for novel antiarrhythmic therapies.
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Affiliation(s)
- Kenneth R Laurita
- The Heart and Vascular Research Center, MetroHealth Campus, Case Western Reserve University, Cleveland, Ohio 44109-1998, USA
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185
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Abstract
Regulation of Calcium (Ca) cycling by the sarcoplasmic reticulum (SR) underlies the control of cardiac contraction during excitation-contraction (E-C) coupling. Moreover, alterations in E-C coupling occurring in cardiac hypertrophy and heart failure are characterized by abnormal Ca-cycling through the SR network. A large body of evidence points to the central role of: a) SERCA and its regulator phospholamban (PLN) in the modulation of cardiac relaxation; b) calsequestrin in the regulation of SR Ca-load; and c) the ryanodine receptor (RyR) Ca-channel in the control of SR Ca-release. The levels or activity of these key Ca-handling proteins are altered in cardiomyopathies, and these changes have been linked to the deteriorated cardiac function and remodeling. Furthermore, genetic variants in these SR Ca-cycling proteins have been identified, which may predispose to heart failure or fatal arrhythmias. This chapter concentrates on the pivotal role of SR Ca-cycling proteins in health and disease with specific emphasis on their recently reported genetic modifiers.
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186
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Killeen MJ, Gurung IS, Thomas G, Stokoe KS, Grace AA, Huang CLH. Separation of early afterdepolarizations from arrhythmogenic substrate in the isolated perfused hypokalaemic murine heart through modifiers of calcium homeostasis. Acta Physiol (Oxf) 2007; 191:43-58. [PMID: 17524066 PMCID: PMC2040229 DOI: 10.1111/j.1748-1716.2007.01715.x] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
Abstract
AIMS We resolved roles for early afterdepolarizations (EADs) and transmural gradients of repolarization in arrhythmogenesis in Langendorff-perfused hypokalaemic murine hearts paced from the right ventricular epicardium. METHODS Left ventricular epicardial and endocardial monophasic action potentials (MAPs) and arrhythmogenic tendency were compared in the presence and absence of the L-type Ca(2+) channel blocker nifedipine (10 nm-1 microm) and the calmodulin kinase type II inhibitor KN-93 (2 microm). RESULTS All the hypokalaemic hearts studied showed prolonged epicardial and endocardial MAPs, decreased epicardial-endocardial APD(90) difference, EADs, triggered beats and ventricular tachycardia (VT) (n = 6). In all spontaneously beating hearts, 100 (but not 10) nm nifedipine reduced both the incidence of EADs and triggered beats from 66.9 +/- 15.7% to 28.3 +/- 8.7% and episodes of VT from 10.8 +/- 6.3% to 1.2 +/- 0.7% of MAPs (n = 6 hearts, P < 0.05); 1 microm nifedipine abolished all these phenomena (n = 6). In contrast programmed electrical stimulation (PES) still triggered VT in six of six hearts with 0, 10 and 100 nm but not 1 microm nifedipine. 1 microm nifedipine selectively reduced epicardial (from 66.1 +/- 3.4 to 46.2 +/- 2.5 ms) but not endocardial APD(90), thereby restoring DeltaAPD(90) from -5.9 +/- 2.5 to 15.5 +/- 3.2 ms, close to normokalaemic values. KN-93 similarly reduced EADs, triggered beats and VT in spontaneously beating hearts to 29.6 +/- 8.9% and 1.7 +/- 1.1% respectively (n = 6) yet permitted PES-induced VT (n = 6), in the presence of a persistently negative DeltaAPD(90). CONCLUSIONS These findings empirically implicate both EADs and triggered beats alongside arrhythmogenic substrate of DeltaAPD(90) in VT pathogenesis at the whole heart level.
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Affiliation(s)
- M J Killeen
- Physiological Laboratory, University of Cambridge, Cambridge, UK.
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187
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Guo T, Ai X, Shannon TR, Pogwizd SM, Bers DM. Intra-sarcoplasmic reticulum free [Ca2+] and buffering in arrhythmogenic failing rabbit heart. Circ Res 2007; 101:802-10. [PMID: 17704210 DOI: 10.1161/circresaha.107.152140] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Smaller Ca2+ transients and systolic dysfunction in heart failure (HF) can be largely explained by reduced total sarcoplasmic reticulum (SR) Ca2+ content ([Ca]SRT). However, it is unknown whether low [Ca]SRT is manifest as reduced: (1) intra-SR free [Ca2+] ([Ca2+]SR), (2) intra-SR Ca2+ buffering, or (3) SR volume (as percentage of cell volume). Here we assess these possibilities in a well-characterized rabbit model of nonischemic HF. In HF versus control myocytes, diastolic [Ca2+]SR is similar at 0.1-Hz stimulation, but the increase in both [Ca2+]SR and [Ca]SRT as frequency increases to 1 Hz is blunted in HF. Direct measurement of intra-SR Ca2+ buffering (by simultaneous [Ca2+]SR and [Ca]SRT measurement) showed no change in HF. Diastolic [Ca]SRT changes paralleled [Ca2+]SR, suggesting that SR volume is not appreciably altered in HF. Thus, reduced [Ca]SRT in HF is associated with comparably reduced [Ca2+]SR. Fractional [Ca2+]SR depletion increased progressively with stimulation frequency in control but was blunted in HF (consistent with the blunted force-frequency relationship in HF). By studying a range of [Ca2+]SR, analysis showed that for a given [Ca]SR, fractional SR Ca2+ release was actually higher in HF. For both control and HF myocytes, SR Ca2+ release terminated when [Ca2+]SR dropped to 0.3 to 0.5 mmol/L during systole, consistent with a role for declining [Ca2+]SR in the dynamic shutoff of SR Ca2+ release. We conclude that low total SR Ca2+ content in HF, and reduced SR Ca2+ release, is attributable to reduced [Ca2+]SR, not to alterations in SR volume or Ca2+ buffering capacity.
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Affiliation(s)
- Tao Guo
- Department of Physiology, Loyola University Chicago, Stritch School of Medicine, Maywood, IL 60153, USA
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188
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Grandi E, Puglisi JL, Wagner S, Maier LS, Severi S, Bers DM. Simulation of Ca-calmodulin-dependent protein kinase II on rabbit ventricular myocyte ion currents and action potentials. Biophys J 2007; 93:3835-47. [PMID: 17704163 PMCID: PMC2084250 DOI: 10.1529/biophysj.107.114868] [Citation(s) in RCA: 83] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/14/2023] Open
Abstract
Ca-calmodulin-dependent protein kinase II (CaMKII) was recently shown to alter Na(+) channel gating and recapitulate a human Na(+) channel genetic mutation that causes an unusual combined arrhythmogenic phenotype in patients: simultaneous long QT syndrome and Brugada syndrome. CaMKII is upregulated in heart failure where arrhythmias are common, and CaMKII inhibition can reduce arrhythmias. Thus, CaMKII-dependent channel modulation may contribute to acquired arrhythmic disease. We developed a Markovian Na(+) channel model including CaMKII-dependent changes, and incorporated it into a comprehensive myocyte action potential (AP) model with Na(+) and Ca(2+) transport. CaMKII shifts Na(+) current (I(Na)) availability to more negative voltage, enhances intermediate inactivation, and slows recovery from inactivation (all loss-of-function effects), but also enhances late noninactivating I(Na) (gain of function). At slow heart rates, with long diastolic time for I(Na) recovery, late I(Na) is the predominant effect, leading to AP prolongation (long QT syndrome). At fast heart rates, where recovery time is limited and APs are shorter, there is little effect on AP duration, but reduced availability decreases I(Na), AP upstroke velocity, and conduction (Brugada syndrome). CaMKII also increases cardiac Ca(2+) and K(+) currents (I(Ca) and I(to)), complicating CaMKII-dependent AP changes. Incorporating I(Ca) and I(to) effects individually prolongs and shortens AP duration. Combining I(Na), I(Ca), and I(to) effects results in shortening of AP duration with CaMKII. With transmural heterogeneity of I(to) and I(to) downregulation in heart failure, CaMKII may accentuate dispersion of repolarization. This provides a useful initial framework to consider pathways by which CaMKII may contribute to arrhythmogenesis.
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Affiliation(s)
- Eleonora Grandi
- Biomedical Engineering Laboratory, Department of Electronics, Computer Science and Systems, University of Bologna, Bologna, Italy
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189
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Chen-Izu Y, Ward CW, Stark W, Banyasz T, Sumandea MP, Balke CW, Izu LT, Wehrens XHT. Phosphorylation of RyR2 and shortening of RyR2 cluster spacing in spontaneously hypertensive rat with heart failure. Am J Physiol Heart Circ Physiol 2007; 293:H2409-17. [PMID: 17630346 DOI: 10.1152/ajpheart.00562.2007] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
As a critical step toward understanding the role of abnormal intracellular Ca(2+) release via the ryanodine receptor (RyR(2)) during the development of hypertension-induced cardiac hypertrophy and heart failure, this study examines two questions: 1) At what stage, if ever, in the development of hypertrophy and heart failure is RyR(2) hyperphosphorylated at Ser(2808)? 2) Does the spatial distribution of RyR(2) clusters change in failing hearts? Using a newly developed semiquantitative immunohistochemistry method and Western blotting, we measured phosphorylation of RyR(2) at Ser(2808) in the spontaneously hypertensive rat (SHR) at four distinct disease stages. A major finding is that hyperphosphorylation of RyR(2) at Ser(2808) occurred only at late-stage heart failure in SHR, but not in age-matched controls. Furthermore, the spacing between RyR(2) clusters was shortened in failing hearts, as predicted by quantitative model simulation to increase spontaneous Ca(2+) wave generation and arrhythmias.
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Affiliation(s)
- Ye Chen-Izu
- Dept. of Internal Medicine, Univ. of Kentucky College of Medicine, 741 S. Limestone St., BBSRB, Rm. B255, Lexington, KY 40536-0509, USA.
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190
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Pereira L, Métrich M, Fernández-Velasco M, Lucas A, Leroy J, Perrier R, Morel E, Fischmeister R, Richard S, Bénitah JP, Lezoualc'h F, Gómez AM. The cAMP binding protein Epac modulates Ca2+ sparks by a Ca2+/calmodulin kinase signalling pathway in rat cardiac myocytes. J Physiol 2007; 583:685-94. [PMID: 17599964 PMCID: PMC2277038 DOI: 10.1113/jphysiol.2007.133066] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
cAMP is a powerful second messenger whose known general effector is protein kinase A (PKA). The identification of a cAMP binding protein, Epac, raises the question of its role in Ca(2+) signalling in cardiac myocytes. In this study, we analysed the effects of Epac activation on Ca(2+) handling by using confocal microscopy in isolated adult rat cardiomyocytes. [Ca(2+)](i) transients were evoked by electrical stimulation and Ca(2+) sparks were measured in quiescent myocytes. Epac was selectively activated by the cAMP analogue 8-(4-chlorophenylthio)-2'-O-methyladenosine-3',5'-cyclic monophosphate (8-CPT). Patch-clamp was used to record the L-type calcium current (I(Ca)), and Western blot to evaluate phosphorylated ryanodine receptor (RyR). [Ca(2+)](i) transients were slightly reduced by 10 microm 8-CPT (F/F(0): decreased from 4.7 +/- 0.5 to 3.8 +/- 0.4, P < 0.05), an effect that was boosted when cells were previously infected with an adenovirus encoding human Epac. I(Ca) was unaltered by Epac activation, so this cannot explain the decreased [Ca(2+)](i) transients. Instead, a decrease in the sarcoplasmic reticulum (SR) Ca(2+) load underlies the decrease in the [Ca(2+)](i) transients. This decrease in the SR Ca(2+) load was provoked by the increase in the SR Ca(2+) leak induced by Epac activation. 8-CPT significantly increased Ca(2+) spark frequency (Ca(2+) sparks s(-1) (100 microm)(-1): from 2.4 +/- 0.6 to 6.9 +/- 1.5, P < 0.01) while reducing their amplitude (F/F(0): 1.8 +/- 0.02 versus 1.6 +/- 0.01, P < 0.001) in a Ca(2+)/calmodulin kinase II (CaMKII)-dependent and PKA-independent manner. Accordingly, we found that Epac increased RyR phosphorylation at the CaMKII site. Altogether, our data reveal a new signalling pathway by which cAMP governs Ca(2+) release and signalling in cardiac myocytes.
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Affiliation(s)
- Laetitia Pereira
- Inserm U637, Physiopathologie Cardiovasculaire, Montpellier, France
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191
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Ferrero P, Said M, Sánchez G, Vittone L, Valverde C, Donoso P, Mattiazzi A, Mundiña-Weilenmann C. Ca2+/calmodulin kinase II increases ryanodine binding and Ca2+-induced sarcoplasmic reticulum Ca2+ release kinetics during beta-adrenergic stimulation. J Mol Cell Cardiol 2007; 43:281-91. [PMID: 17643448 PMCID: PMC2045504 DOI: 10.1016/j.yjmcc.2007.05.022] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/28/2007] [Revised: 05/25/2007] [Accepted: 05/31/2007] [Indexed: 10/23/2022]
Abstract
We aimed to define the relative contribution of both PKA and Ca(2+)/calmodulin-dependent protein kinase II (CaMKII) cascades to the phosphorylation of RyR2 and the activity of the channel during beta-adrenergic receptor (betaAR) stimulation. Rat hearts were perfused with increasing concentrations of the beta-agonist isoproterenol in the absence and the presence of CaMKII inhibition. CaMKII was inhibited either by preventing the Ca(2+) influx to the cell by low [Ca](o) plus nifedipine or by the specific inhibitor KN-93. We immunodetected RyR2 phosphorylated at Ser2809 (PKA and putative CaMKII site) and at Ser2815 (CaMKII site) and measured [(3)H]-ryanodine binding and fast Ca(2+) release kinetics in sarcoplasmic reticulum (SR) vesicles. SR vesicles were isolated in conditions that preserved the phosphorylation levels achieved in the intact heart and were actively and equally loaded with Ca(2+). Our results demonstrated that Ser2809 and Ser2815 of RyR2 were dose-dependently phosphorylated under betaAR stimulation by PKA and CaMKII, respectively. The isoproterenol-induced increase in the phosphorylation of Ser2815 site was prevented by the PKA inhibitor H-89 and mimicked by forskolin. CaMKII-dependent phosphorylation of RyR2 (but not PKA-dependent phosphorylation) was responsible for the beta-induced increase in the channel activity as indicated by the enhancement of the [(3)H]-ryanodine binding and the velocity of fast SR Ca(2+) release. The present results show for the first time a dose-dependent increase in the phosphorylation of Ser2815 of RyR2 through the PKA-dependent activation of CaMKII and a predominant role of CaMKII-dependent phosphorylation of RyR2, over that of PKA-dependent phosphorylation, on SR-Ca(2+) release during betaAR stimulation.
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Affiliation(s)
- Paola Ferrero
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, 60 y 120, 1900 La Plata, Argentina
| | - Matilde Said
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, 60 y 120, 1900 La Plata, Argentina
| | - Gina Sánchez
- Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Casilla 16038, Santiago 9, Chile
| | - Leticia Vittone
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, 60 y 120, 1900 La Plata, Argentina
| | - Carlos Valverde
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, 60 y 120, 1900 La Plata, Argentina
| | - Paulina Donoso
- Instituto de Ciencias Biomédicas, Facultad de Medicina, Universidad de Chile, Casilla 16038, Santiago 9, Chile
| | - Alicia Mattiazzi
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, 60 y 120, 1900 La Plata, Argentina
| | - Cecilia Mundiña-Weilenmann
- Centro de Investigaciones Cardiovasculares, Facultad de Ciencias Médicas, Universidad Nacional de La Plata, 60 y 120, 1900 La Plata, Argentina
- * Corresponding author. Tel./fax: +54 221 483 4833. E-mail address: (C. Mundiña-Weilenmann)
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192
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Abstract
Cyclic AMP regulates a vast number of distinct events in all cells. Early studies established that its hydrolysis by cyclic nucleotide phosphodiesterases (PDEs) controlled both the magnitude and the duration of its influence. Recent evidence shows that PDEs also act as coincident detectors linking cyclic-nucleotide- and non-cyclic-nucleotide-based cellular signaling processes and are tethered with great selectively to defined intracellular structures, thereby integrating and spatially restricting their cellular effects in time and space. Although 11 distinct families of PDEs have been defined, and cells invariably express numerous individual PDE enzymes, a large measure of our increased appreciation of the roles of these enzymes in regulating cyclic nucleotide signaling has come from studies on the PDE4 family. Four PDE4 genes encode more than 20 isoforms. Alternative mRNA splicing and the use of different promoters allows cells the possibility of expressing numerous PDE4 enzymes, each with unique amino-terminal-targeting and/or regulatory sequences. Dominant negative and small interfering RNA-mediated knockdown strategies have proven that particular isoforms can uniquely control specific cellular functions. Thus the protein kinase A phosphorylation status of the beta(2) adrenoceptor and, thereby, its ability to switch its signaling to extracellular signal-regulated kinase activation, is uniquely regulated by PDE4D5 in cardiomyocytes. We describe how cardiomyocytes and vascular smooth muscle cells selectively vary both the expression and the catalytic activities of PDE4 isoforms to regulate their various functions and how altered regulation of these processes can influence the development, or resolution, of cardiovascular pathologies, such as heart failure, as well as various vasculopathies.
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MESH Headings
- 3',5'-Cyclic-AMP Phosphodiesterases/chemistry
- 3',5'-Cyclic-AMP Phosphodiesterases/metabolism
- A Kinase Anchor Proteins
- Adaptor Proteins, Signal Transducing/metabolism
- Animals
- Arrestins/metabolism
- Cardiovascular System/enzymology
- Cardiovascular System/metabolism
- Cyclic AMP/metabolism
- Cyclic Nucleotide Phosphodiesterases, Type 4
- Humans
- Isoenzymes/metabolism
- Muscle, Smooth, Vascular/cytology
- Muscle, Smooth, Vascular/enzymology
- Myocytes, Cardiac/enzymology
- Myocytes, Smooth Muscle/enzymology
- Myocytes, Smooth Muscle/physiology
- Ryanodine Receptor Calcium Release Channel/metabolism
- Signal Transduction
- Vasoconstriction
- beta-Arrestins
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Affiliation(s)
- Miles D Houslay
- Molecular Pharmacology Group, Division of Biochemistry and Molecular Biology, Institute of Biomedical and Life Sciences, University of Glasgow, Glasgow G12 8QQ, Scotland, UK.
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193
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Abstract
Triggered activity in cardiac muscle and intracellular Ca2+ have been linked in the past. However, today not only are there a number of cellular proteins that show clear Ca2+ dependence but also there are a number of arrhythmias whose mechanism appears to be linked to Ca2+-dependent processes. Thus we present a systematic review of the mechanisms of Ca2+ transport (forward excitation-contraction coupling) in the ventricular cell as well as what is known for other cardiac cell types. Second, we review the molecular nature of the proteins that are involved in this process as well as the functional consequences of both normal and abnormal Ca2+ cycling (e.g., Ca2+ waves). Finally, we review what we understand to be the role of Ca2+ cycling in various forms of arrhythmias, that is, those associated with inherited mutations and those that are acquired and resulting from reentrant excitation and/or abnormal impulse generation (e.g., triggered activity). Further solving the nature of these intricate and dynamic interactions promises to be an important area of research for a better recognition and understanding of the nature of Ca2+ and arrhythmias. Our solutions will provide a more complete understanding of the molecular basis for the targeted control of cellular calcium in the treatment and prevention of such.
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Affiliation(s)
- Henk E D J Ter Keurs
- Department of Medicine, Physiology and Biophysics, University of Calgary, Alberta, Canada
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194
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195
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Yamaguchi N, Meissner G. Does Ca2+/calmodulin-dependent protein kinase deltac activate or inhibit the cardiac ryanodine receptor ion channel? Circ Res 2007; 100:293-5. [PMID: 17307966 DOI: 10.1161/01.res.0000259327.56377.55] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
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196
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Maier LS, Bers DM. Role of Ca2+/calmodulin-dependent protein kinase (CaMK) in excitation–contraction coupling in the heart. Cardiovasc Res 2007; 73:631-40. [PMID: 17157285 DOI: 10.1016/j.cardiores.2006.11.005] [Citation(s) in RCA: 244] [Impact Index Per Article: 14.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/05/2006] [Revised: 11/03/2006] [Accepted: 11/06/2006] [Indexed: 11/27/2022] Open
Abstract
Calcium (Ca(2+)) is the central second messenger in the translation of electrical signals into mechanical activity of the heart. This highly coordinated process, termed excitation-contraction coupling or ECC, is based on Ca(2+)-induced Ca(2+) release from the sarcoplasmic reticulum (SR). In recent years it has become increasingly clear that several Ca(2+)-dependent proteins contribute to the fine tuning of ECC. One of these is the Ca(2+)/calmodulin-dependent protein kinase (CaMK) of which CaMKII is the predominant cardiac isoform. During ECC CaMKII phosphorylates several Ca(2+) handling proteins with multiple functional consequences. CaMKII may also be co-localized to distinct target proteins. CaMKII expression as well as activity are reported to be increased in heart failure and CaMKII overexpression can exert distinct and novel effects on ECC in the heart and in isolated myocytes of animals. In the present review we summarize important aspects of the role of CaMKII in ECC with an emphasis on recent novel findings.
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Affiliation(s)
- Lars S Maier
- Abt. Kardiologie & Pneumologie / Herzzentrum, Georg-August-Universität Göttingen, 37075 Göttingen, Germany.
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197
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Grimm M, El-Armouche A, Zhang R, Anderson ME, Eschenhagen T. Reduced contractile response to α1-adrenergic stimulation in atria from mice with chronic cardiac calmodulin kinase II inhibition. J Mol Cell Cardiol 2007; 42:643-52. [PMID: 17292391 DOI: 10.1016/j.yjmcc.2006.12.010] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/18/2006] [Revised: 12/15/2006] [Accepted: 12/20/2006] [Indexed: 10/01/2022]
Abstract
The sustained positive inotropic effect of alpha-adrenoceptor agonists in the heart is associated with a small increase in intracellular Ca(2+) transients together with a larger sensitization of myofilaments to Ca(2+). The multifunctional Ca(2+) and calmodulin-dependent protein kinase II (CaMKII) could contribute to this effect, either by affecting the Ca(2+) release (ryanodine receptor) or by an uptake mechanism (via phospholamban [PLB] and SR Ca(2+) ATPase). Here we examined the role of CaMKII in the positive inotropic effect of the alpha-adrenoceptor agonist phenylephrine in left atria isolated from a genetic mouse model of cardiac CaMKII inhibition (AC3-I). Compared to atria from wild-type (WT) or AC3-C (scrambled peptide), AC3-I atria showed the following abnormalities. PLB phosphorylation at Thr17, a known CaMKII target, was significantly lower ( approximately 20%). Post-rest (30 s, 1 Hz, 37 degrees C) potentiation of force was absent (AC3-C, 190% of pre-rest amplitude). Basal force was approximately 20% lower at 1.8 mM Ca(2+), but normal at high Ca(2+) concentration (>4.5 mM). The maximal positive inotropic effect of phenylephrine, which was more pronounced at low frequencies in WT and AC3-C atria, lost its frequency dependence (1 Hz to 8 Hz). Thus, the effect of phenylephrine was reduced by approximately 50% at 1 Hz, but was normal at 8 Hz. All three groups showed a negative force-frequency relation, and did not differ in the frequency-dependent acceleration of relaxation. Our data indicate a role of CaMKII in post-rest potentiation and the positive inotropic effect of alpha-adrenergic stimulation at low frequencies.
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Affiliation(s)
- Michael Grimm
- Institute of Experimental and Clinical Pharmacology and Toxicology, University Medical Center Hamburg-Eppendorf, Hamburg, Germany
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198
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Curran J, Hinton MJ, Ríos E, Bers DM, Shannon TR. β-Adrenergic Enhancement of Sarcoplasmic Reticulum Calcium Leak in Cardiac Myocytes Is Mediated by Calcium/Calmodulin-Dependent Protein Kinase. Circ Res 2007; 100:391-8. [PMID: 17234966 DOI: 10.1161/01.res.0000258172.74570.e6] [Citation(s) in RCA: 232] [Impact Index Per Article: 13.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Enhanced cardiac diastolic Ca leak from the sarcoplasmic reticulum (SR) ryanodine receptor may reduce SR Ca content and contribute to arrhythmogenesis. We tested whether β-adrenergic receptor (β-AR) agonists increased SR Ca leak in intact rabbit ventricular myocytes and whether this depends on protein kinase A or Ca/calmodulin-dependent protein kinase II (CaMKII) activity. SR Ca leak was assessed by acute block of the ryanodine receptor by tetracaine and assessment of the consequent shift of Ca from cytosol to SR (measured at various SR Ca loads induced by varying frequency). Cytosolic [Ca] ([Ca]
i
) and SR Ca load ([Ca]
SRT
) were assessed using fluo-4. β-AR activation by isoproterenol dramatically increased SR Ca leak. However, this effect was not inhibited by blocking protein kinase A by H-89, despite the expected reversal of the isoproterenol-induced enhancement of Ca transient amplitude and [Ca]
i
decline rate. In contrast, inhibitors of CaMKII, KN-93, or autocamtide-2–related inhibitory peptide II or β-AR blockade reversed the isoproterenol-induced enhancement of SR Ca leak, and CaMKII inhibition could even reduce leak below control levels. Forskolin, which bypasses the β-AR in activating adenylate cyclase and protein kinase A, did not increase SR Ca leak, despite robust enhancement of Ca transient amplitude and [Ca]
i
decline rate. The results suggest that β-AR stimulation enhances diastolic SR Ca leak in a manner that is (1) CaMKII dependent, (2) not protein kinase A dependent, and 3) not dependent on bulk [Ca]
i
.
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MESH Headings
- Adrenergic beta-Agonists/pharmacology
- Animals
- Benzylamines/pharmacology
- Calcium/metabolism
- Calcium Channels, L-Type/physiology
- Calcium Signaling/drug effects
- Calcium Signaling/physiology
- Calcium-Calmodulin-Dependent Protein Kinase Type 2
- Calcium-Calmodulin-Dependent Protein Kinases/antagonists & inhibitors
- Calcium-Calmodulin-Dependent Protein Kinases/physiology
- Calmodulin/physiology
- Cells, Cultured/drug effects
- Cells, Cultured/metabolism
- Colforsin/pharmacology
- Cyclic AMP-Dependent Protein Kinases/antagonists & inhibitors
- Cyclic AMP-Dependent Protein Kinases/physiology
- Diastole
- Heart Failure/etiology
- Isoproterenol/pharmacology
- Isoquinolines/pharmacology
- Myocardial Contraction/drug effects
- Myocardial Contraction/physiology
- Myocardium/metabolism
- Myocytes, Cardiac/drug effects
- Myocytes, Cardiac/metabolism
- Peptides/pharmacology
- Phosphorylation
- Protein Processing, Post-Translational/physiology
- Rabbits
- Receptors, Adrenergic, beta/drug effects
- Receptors, Adrenergic, beta/physiology
- Ryanodine Receptor Calcium Release Channel/metabolism
- Sarcoplasmic Reticulum/metabolism
- Signal Transduction/drug effects
- Signal Transduction/physiology
- Sulfonamides/pharmacology
- Tetracaine/pharmacology
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Affiliation(s)
- Jerald Curran
- Rush University Medical Center, Chicago, IL 60611, USA
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199
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Yang D, Zhu WZ, Xiao B, Brochet DXP, Chen SRW, Lakatta EG, Xiao RP, Cheng H. Ca
2+
/Calmodulin Kinase II-Dependent Phosphorylation of Ryanodine Receptors Suppresses Ca
2+
Sparks and Ca
2+
Waves in Cardiac Myocytes. Circ Res 2007; 100:399-407. [PMID: 17234969 DOI: 10.1161/01.res.0000258022.13090.55] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The multifunctional Ca
2+
/calmodulin-dependent protein kinase II δ
C
(CaMKIIδ
C
) is found in the macromolecular complex of type 2 ryanodine receptor (RyR2) Ca
2+
release channels in the heart. However, the functional role of CaMKII-dependent phosphorylation of RyR2 is highly controversial. To address this issue, we expressed wild-type, constitutively active, or dominant-negative CaMKIIδ
C
via adenoviral gene transfer in cultured adult rat ventricular myocytes. CaMKII-mediated phosphorylation of RyR2 was reduced, enhanced, or unaltered by dominant-negative, constitutively active, or wild-type CaMKIIδ
C
expression, whereas phosphorylation of phospholamban at Thr17, an endogenous indicator of CaMKII activity, was at 73%, 161%, or 115% of the control group expressing β-galactosidase (β-gal), respectively. In parallel with the phospholamban phosphorylation, the decay kinetics of global Ca
2+
transients was slowed, accelerated, or unchanged, whereas spontaneous Ca
2+
spark activity was hyperactive, depressed, or unchanged in dominant-negative, constitutively active, or wild-type CaMKIIδ
C
groups, respectively. When challenged by high extracellular Ca
2+
, both wild-type and constitutively active CaMKIIδ
C
protected the cells from store overload-induced Ca
2+
release, manifested by a ≈60% suppression of Ca
2+
waves (at 2 to 20 mmol/L extracellular Ca
2+
) in spite of an elevated sarcoplasmic reticulum Ca
2+
content, whereas dominant-negative CaMKIIδ
C
promoted Ca
2+
wave production (at 20 mmol/L Ca
2+
) with significantly depleted sarcoplasmic reticulum Ca
2+
. Taken together, our data support the notion that CaMKIIδ
C
negatively regulates RyR2 activity and spontaneous sarcoplasmic reticulum Ca
2+
release, thereby affording a negative feedback that stabilizes local and global Ca
2+
-induced Ca
2+
release in the heart.
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Affiliation(s)
- Dongmei Yang
- Laboratory of Cardiovascular Science, National Institute on Aging, NIH, Baltimore, MD 21224, USA
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200
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Dulhunty AF, Beard NA, Pouliquin P, Casarotto MG. Agonists and antagonists of the cardiac ryanodine receptor: Potential therapeutic agents? Pharmacol Ther 2007; 113:247-63. [PMID: 17055586 DOI: 10.1016/j.pharmthera.2006.08.007] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2006] [Accepted: 08/16/2006] [Indexed: 10/24/2022]
Abstract
This review addresses the potential use of the intracellular ryanodine receptor (RyR) Ca(2+) release channel as a therapeutic target in heart disease. Heart disease encompasses a wide range of conditions with the major contributors to mortality and morbidity being ischaemic heart disease and heart failure (HF). In addition there are many rare, but devastating conditions, some of which are either genetically linked to the RyR and its regulatory proteins or involve drug-induced modification of the proteins. The defects in Ca(2+) signalling vary with the nature of the heart disease and the stage in its progress and therefore specific corrections require different modifications of Ca(2+) signalling. Compounds that activate the RyR are potential inotropic agents to increase the Ca(2+) transient and strength of contraction. Compounds that reduce RyR activity are potentially useful in conditions where excess RyR activity initiates arrhythmias, or depletes the Ca(2+) store, as in end stage HF. It has recently been discovered that the cardio-protective action of the drug JTV519 can be attributed partly to its ability to stabilise the interaction between the RyR and the 12.6 kDa binding protein for the commonly used immunosuppressive drug FK506 (FKBP12.6, known as tacrolimus). This has established the credibility of the RyR as a therapeutic target. We explore the possibility that mutations causing the rare RyR-linked arrhythmias will open the door to identification of novel RyR-based therapeutic agents. The use of regulatory binding sites within the RyR complex or on its associated proteins as templates for drug design is discussed.
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Affiliation(s)
- Angela F Dulhunty
- Division of Molecular Bioscience, John Curtin School of Medical Research, Australian National University, P.O. Box 334, ACT, 2601, Australia
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