Posts Tagged: calcium

Calcium and Excitation-Contraction Coupling in the Heart

Calcium and Excitation-Contraction Coupling in the Heart

David A. Eisner, Jessica L. Caldwell, Kornél Kistamás, Andrew W. Trafford

Structures involved in Ca cycling. A, Schematic diagram. This shows surface membrane, transverse tubule, sarcoplasmic reticulum (SR), and mitochondria, as well as the various channels and transporters mentioned in the text. B, High-resolution transverse section of a ventricular myocyte showing t-tubule network. Reprinted from Jayasinghe et al39 with permission of the publisher. Copyright ©2009, Biophysical Society. C, Cartoon of dyad emphasizing the major proteins involved in Ca cycling. B-AR indicates beta adrenoceptor; MCU, mitochondrial Ca uniporter; NCX, sodium–calcium exchange; NCLX, mitochondrial Na–Ca exchange; PMCA, plasma membrane Ca-ATPase; RyR, ryanodine receptor; and SERCA, sarco/endoplasmic reticulum Ca-ATPase. [Powerpoint File]

PI3K and Calcium Signaling in Cardiovascular Disease

PI3K and Calcium Signaling in Cardiovascular Disease

Alessandra Ghigo, Muriel Laffargue, Mingchuan Li, Emilio Hirsch

Class I PI3Ks (phosphoinositide 3-kinases). Class I PI3Ks are obligate heterodimers composed by a p110 catalytic module and an adaptor subunit. Depending on the nature of the adaptor and of the activating membrane receptor, class I PI3Ks can be subgrouped into class IA and IB. Class IA includes PI3Kα, β, and δ, which are coupled to a p85 regulatory subunit and are engaged by tyrosine kinase receptors (RTKs). On the contrary, the unique member of class IB, PI3Kγ, binds to either p101 or p87 that, by tethering p110γ to the Gβγ subunit of G protein-coupled receptors (GPCRs), ensure the full enzyme activation. All class I isoenzymes phosphorylate PIP2 PtdIns(4,5)P2 to produce PIP3 that, in turn, serves as a docking site for intracellular effectors carrying a lipid-binding domain, such as Akt (protein kinase B). Activated Akt ultimately initiates a wide spectrum of biological events, ranging from proliferation, survival, and metabolic regulation. [Powerpoint File]

PI3K and Calcium Signaling in Cardiovascular Disease

PI3K and Calcium Signaling in Cardiovascular Disease

Alessandra Ghigo, Muriel Laffargue, Mingchuan Li, Emilio Hirsch

PI3K (phosphoinositide 3-kinase)-mediated compartmentalization of β-adrenergic receptors-dependent Ca2+ responses in cardiomyocytes. Class IB PI3Kγ restrains Ca2+ signaling in response to β-adrenergic stimuli via a kinase-unrelated mechanism. This relies on the ability of PI3Kγ to anchor PDE (phosphodiesterase)3 or 4 to their activator PKA in specific subcellular compartments and to promote PKA-mediated activation of PDEs (active PDE3/4). The ensuing cyclic AMP (cAMP) reduction limits PKA-mediated phosphorylation and activation of Ca2+-handling proteins, including L-type Ca2+ channel (LTCC) and PLN (phospholamban; left). In heart failure, a functional decay in PI3Kγ-directed protein–protein interactions limits PDE activity (inactive PDE3/4), leading to abnormal cAMP accumulation and uncontrolled PKA activity close to LTCC and PLN, which culminate in arrhythmogenic Ca2+ release events (right). PLN indicates phospholamban; and SR, sarcoplasmic reticulum. [Powerpoint File]

Thirty Years of Saying NO: Sources, Fate, Actions, and Misfortunes of the Endothelium-Derived Vasodilator Mediator

Thirty Years of Saying NO: Sources, Fate, Actions, and Misfortunes of the Endothelium-Derived Vasodilator Mediator

Paul M. Vanhoutte, Yingzi Zhao, Aimin Xu, Susan W.S. Leung

Regulation of vascular tone by endothelium-derived nitric oxide (NO). Top, Physical factors (increases in shear stress and temperature lowering) and neurohumoral mediators (through activation of specific endothelial cell membrane receptors) cause instantaneous increases in the release of endothelium-derived NO by endothelial nitric oxide synthase (eNOS). Color code: Signals leading to activation of eNOS dependent mainly on increases in Ca2+ concentration, mainly on post-translational modifications or on both are indicated by blue, yellow, and green, respectively. Image derived from Vanhoutte et al14 and modified from Zhao et al29 (Copyright ©2015, The Authors). Bottom, The contraction of vascular smooth muscle cells is initiated by increases in the intracellular calcium (Ca2+) concentration either from internal stores (sarcoplasmic reticulum [SR]) or by influx into the cell after opening of calcium channels in the cell membrane. The intracellular free calcium ions bind to calmodulin (CaM) and the calcium–calmodulin complex activates myosin light-chain kinase; when activated the latter phosphorylates myosin light chain, which leads to cross-bridge formation between the myosin heads and the actin filaments. Cross-bridge formation results in contraction of the smooth muscle cell. NO modulates the contraction process in different ways: (A) NO stimulates soluble guanylyl cyclase (sGC) in the vascular smooth muscle cells which produces cGMP. Cyclic GMP activates protein kinase G (PKG), preventing calcium influx through voltage-dependent calcium channels and calcium release mediated by inositol 1,4,5-trisphosphate (IP3) receptors (IP3R). In addition, PKG not only activates the calcium-ATPase on the cell membrane and the sarco/endoplasmic reticulum calcium-ATPase (SERCA) accelerating the efflux of cytosolic calcium outside the cell and its reuptake into the sarcoplasmic reticulum (SR), respectively, but also opens large-conductance calcium-activated potassium channels resulting in hyperpolarization, which in turn prevents the opening of voltage-dependent L-type channels and hence calcium influx. The resulting decrease in free intracellular calcium ion concentration inactivates calmodulin and thus myosin light-chain kinase. Calcium depletion also augments the activity of myosin light-chain phosphatase (MLCP). The actin–myosin cross-bridges are interrupted and the vascular smooth muscle cell relaxes and (B) NO also S-nitrosylates (SNO) intracellular proteins: (1) SERCA with resulting accelerated calcium depletion; NO also facilitate the S-glutathionylation (SSG) of SERCA; (2) G-protein–coupled receptors (GPCR) with reduced binding of ligands (A) or blunted G-protein coupling; (3) G-protein–coupled receptor kinase 2 (GRK2) preventing desensitization and internalization of β-adrenoceptors; and (4) β-arrestin 2 increasing receptor-internalization. Modified from Zhao et al29 (Copyright ©2015, The Authors). α indicates α-adrenergic receptor; 5HT, serotonin (5-hydroxytryptamine); 5HT1d, serotoninergic (5 hydroxytryptamine) receptor 1D subtypes; ACh, acetylcholine; Ang1–7, angiotensin1–7; AdipoR, adiponectin receptor; AVP, arginine vasopressin; B, kinin receptor; E, epinephrine; EP4, prostaglandin E2-receptor 4; ER, nongenomic estrogen receptor; ET, endothelin-1; ETb, endothelin-receptor B subtypes; GLP, glucagon-like peptide-1, glucagon-like peptide receptor; GPR55, G-protein–coupled receptor 55; H, histaminergic receptor; HDL,_wp_link_placeholder high-density lipoproteins; IP, prostacyclin receptor; IR1, insulin receptor; M, muscarinic receptor; Mas, Mas receptor; MC, melanocortin receptor; NE, norepinephrine; P, purinergic receptor; PAR, protease activated receptor; PGE2, prostaglandin E2; PGI2, prostacyclin; SP1, sphingosine 1-phosphate; TRP, transient potential receptor V4; V, vasopressin receptor; VEGF, vascular endothelial growth factor; VEGFR, VEGF-receptor; VD, vitamin D; and VDR, vitamin D receptor. [Powerpoint File]

Thirty Years of Saying NO: Sources, Fate, Actions, and Misfortunes of the Endothelium-Derived Vasodilator Mediator

Thirty Years of Saying NO: Sources, Fate, Actions, and Misfortunes of the Endothelium-Derived Vasodilator Mediator

Paul M. Vanhoutte, Yingzi Zhao, Aimin Xu, Susan W.S. Leung

Dysfunction of endothelial nitric oxide synthase (eNOS): protein changes. Examples of factors increasing or reducing the mRNA expression, the protein presence and the degree of dimerization of endothelial NO synthase (eNOS). The green and red arrows indicate facilitation or inhibition of NO-dependent dilatations, respectively. ALK1 indicates transforming growth factor-β receptor; ALK5, transforming growth factor-β3 receptor; α-CGRP, α-calcitonin gene–related peptide; AP-1, activator protein-1; BH4, tetrahydrobiopterin; CaMKII, calcium/calmodulin-dependent protein kinases II; eEF1-α, eukaryotic translation elongation factor 1 α; ER, estrogen receptor; GLP, glucagon-like peptide; H2O2, hydrogen peroxide; IR1, insulin receptor 1; JAK2, janus kinase II; KLF2, Krüppel-like factor-2; KDM, histone demethylase; LCN2, lipocalin-2; JNK, c-Jun NH2-terminal mitogen-activated protein kinase; MAPK, mitogen-activated protein kinase; L-arg, L-arginine; MC1, melanocortin 1 receptor; miR, microribonucleic acid; NFκB, nuclear factor κB; ox-LDL, oxidized low-density lipoproteins; P-Akt, phosphor-protein kinase B; PI3K, phosphoinositide 3-kinase; PHLPP2, phosphotyrosine-binding domain and leucine-rich repeat protein phosphatase 2; PTBP-1, polypyrimidine tract-binding protein 1; R, receptor; ROS, reactive oxygen species; SIRT1, silent mating-type information regulation 2 homologue 1; SNO, S-nitrosylation; Sp1, specificity protein 1; SSG, S-glutathionylation; TGF-β, transforming growth factor-β; TNF-α, tumor necrosis factor-α; TH, thyroid hormone; THR, thyroid hormone receptor; and VDR, vitamin D receptor. [Powerpoint File]

Role of Sodium and Calcium Dysregulation in Tachyarrhythmias in Sudden Cardiac Death

Role of Sodium and Calcium Dysregulation in Tachyarrhythmias in Sudden Cardiac Death

Stefan Wagner, Lars S. Maier, Donald M. Bers

Schematic diagram of cellular Ca fluxes during excitation–contraction coupling. Ca entry via L-type Ca channels triggers Ca-induced Ca release from the sarcoplasmic reticulum (SR), which results in myofilament activation. For relaxation, cytosolic Ca is transported into the SR via SR Ca-ATPase (SERCA2a) and into the extracellular space via sarcolemmal Na/Ca exchanger. Reprinted from Bers6 with permission of the publisher. Copyright ©2000, Wolters Kluwer Health. [Poweroint File]

Role of Sodium and Calcium Dysregulation in Tachyarrhythmias in Sudden Cardiac Death

Role of Sodium and Calcium Dysregulation in Tachyarrhythmias in Sudden Cardiac Death

Stefan Wagner, Lars S. Maier, Donald M. Bers

Proarrhythmogenic mechanisms of enhanced late INa. In systole (upper panel), enhanced late INa leads to action potential (AP) prolongation (1). The longer AP plateau phase increases the likelihood of ICa reactivation (2), which may lead to early afterdepolarizations (EAD, 3). Lower panel, The increased amount of Na influx also results in increased intracellular Na (1), which impairs Ca elimination (2) by the Na/Ca exchanger (either less forward or even increased reverse mode activity). In diastole, the increased intracellular Ca facilitates SR Ca leak (3), which could lead to transient inward current (ITi) by the Na/Ca exchanger (4). The latter can result in delayed afterdepolarizations (DAD, 5). [Poweroint File]

Regulated Necrotic Cell Death: The Passive Aggressive Side of Bax and Bak

Regulated Necrotic Cell Death: The Passive Aggressive Side of Bax and Bak

Jason Karch, Jeffery D. Molkentin

Mitochondrial permeability transition pore (MPTP)-dependent necrotic pathway. When a cell receives a stress that leads to increased levels of intracellular calcium, the mitochondrial calcium uniporter (MCU) takes up the calcium into the matrix of the mitochondria where it can trigger MPTP opening through cyclophilin D (CypD). The MPTP is thought to be composed of the F1F0 ATP synthase regulated by ANT and the mitochondrial phosphate carrier (PiC). On prolonged opening of the MPTP, there is an osmotic alteration and mitochondrial swelling and dysfunction occur with loss of ATP production and reactive oxygen species (ROS) generation. MPTP-dependent mitochondrial dysfunction requires the presence of Bax or Bak on the outer mitochondrial membrane. Therefore, proteins that affect the content of Bax/Bak on the outer mitochondrial membrane, such as the prosurvival the Bcl-2 family members, can secondarily affect MPTP-dependent mitochondrial dysfunction. ANT indicates adenine nucleotide translocator; BH, Bcl-2 homology; IMM, inner mitochondrial membrane; IMS, intramitochondrial membrane space; and OMM, outer mitochondrial membrane. [Powerpoint File]

Regulated Necrotic Cell Death: The Passive Aggressive Side of Bax and Bak

Regulated Necrotic Cell Death: The Passive Aggressive Side of Bax and Bak

Jason Karch, Jeffery D. Molkentin

Necroptotic pathway. The combinatorial treatment with an apoptotic death receptor ligand and a caspase inhibitor leads to necroptosis with receptor-interacting protein kinase 1 (RIP1) activation. Without the caspase inhibitor present, caspase 8 would normally cleave and inactivate RIP1. When RIP1 is left unchecked in the presence of a caspase inhibitor, it complexes with RIP3 and together they lead to the phosphorylation and activation of mixed lineage kinase like (MLKL). MLKL is a required protein for necroptosis. [Powerpoint File]

Cellular and Molecular Electrophysiology of Atrial Fibrillation Initiation, Maintenance, and Progression

Cellular and Molecular Electrophysiology of Atrial Fibrillation Initiation, Maintenance, and Progression

Jordi Heijman*, Niels Voigt*, Stanley Nattel, Dobromir Dobrev

Arrhythmogenic changes in atrial fibroblasts. Disease- and atrial fibrillation (AF)–related remodeling promotes fibroblast differentiation into myofibroblasts, involving altered expression of several ion channel proteins and microRNAs (miRs). Myofibroblasts facilitate AF maintenance by promoting re-entry through fibrosis/collagen deposition, as well as paracrine and direct electrotonic interactions with cardiomyocytes. Ado indicates aldosterone; Ang-II, angiotensin II; TGFβ1, transforming growth factor β1; TNFα, tumor necrosis factor α; TRPC3, transient receptor potential (TRP) canonical-3; and TRPM, TRP melastatin–related 7. [Powerpoint File]

Genetically Encoded Ca2+ Indicators in Cardiac Myocytes

Genetically Encoded Ca2+ Indicators in Cardiac Myocytes

Lars Kaestner, Anke Scholz, Qinghai Tian, Sandra Ruppenthal, Wiebke Tabellion, Kathrina Wiesen, Hugo A. Katus, Oliver J. Müller, Michael I. Kotlikoff, Peter Lipp

In vivo Ca2+ imaging using genetically encoded sensors. A–H, Transgenic zebrafish embryos expressing GCaMP1 underwent Ca2+ imaging experiments. In animals expressing the dococs226 mutant (dco−/−), disarrayed cardiac impulse propagation was evident. A, Brightfield micrographs of 48 hours post fertilization (hpf) wild-type (WT) and dco−/− embryos. The black arrow indicates pericardial edema. B, Schematic diagram illustrating the modular structure of Cx46. A connexon consists of 4 transmembrane domains (M1–M4). The M3 domain is the major pore-lining domain. The red asterisk marks the site of the s226 mutation. C–E, Optical maps of Ca2+ transient propagation during a single cardiac cycle, represented as isochromes every 20 ms in 60 hpf embryos carrying the Tg(cmlc2:gCaMP)s878 reporter and (C) WT at the dco locus (WT), (D) dcos226 homozygous mutant (dco), or (E) WT with dcos226 mutant cardiomyocytes carrying the Tg(cmlc2:dsRed)s879 reporter in the ventricle (dco→WT). The black arrow shows the normal direction of ventricular cardiac conduction. The numbers indicate the temporal sequence of Ca2+ transients. Cardiac conduction across the WT ventricle proceeds uniformly from the atrioventricular (AV) canal to the outflow tract (OT), whereas cardiac conduction travels aberrantly through the dcos226 mutant ventricle. Transplanted dcos226 mutant cardiomyocytes disrupt the organized AV to OT conduction in the WT ventricle. The white asterisk marks the location of transplanted dco mutant cardiomyocytes in the WT ventricle, as illustrated in G and H. F and H, Fluorescent micrographs of the dco→WT mosaic heart imaged in E. F, Green fluorescence shows the WT host ventricle and (G) donor-derived dcos226 mutant cardiomyocytes expressing Tg(cmlc2:dsRed)s879. H, An overlay of green and red fluorescence images reveals that the donor-derived dcos226 mutant cardiomyocytes are located at the outer curvature of the ventricle near the AV canal, where cardiac conduction is disrupted in the WT host ventricle (E). I–L, Ca2+ signaling in the heart from a transgenic mouse line expressing GCaMP2. I, Time sequence of fluorescence images during a single cardiac cycle in an anesthetized and ventilated mouse. Images were obtained at 128 Hz with an Andor iXon camera. Note the lack of fluorescence in cardiac vasculature and the decline in the ventricular Ca2+ transient during the beginning of the atrial systole (very top of image). J, GCaMP2 fluorescence in a 1-day-old mouse in vivo. Images at peak atrial and ventricular systole are shown from a series obtained at 33 Hz. The sequences show before (top) and directly after (bottom) direct application of 10 μmol/L isoproterenol (Iso). The heart is illuminated obliquely from the left side of the camera, highlighting the right atrium (RA) and ventricle (RV); each series was separately scaled to 0 to 255 (left atrium [LA]). K, Left, Atrial fluorescence transients recorded in the experiment shown in J; right, transients recorded from the same heart after direct application of 10 μmol/L Iso. L, In vivo images from a phenotypically normal heart after transgene induction by dox removal. The images show diastole and peak atrial (A) and ventricular (V) systole. Continuous ventricular fluorescence from the full experiment is shown below. The color scale in I applies throughout. Reproduced from Tallini et al18 and Chi et al,97 copyright 2006 and 2010, respectively. [Powerpoint File]

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Min Luo, Mark E. Anderson

Ca2+ homeostasis and excitation-contraction coupling (ECC). The ECC process is initiated when an action potential (AP) excites the myocyte cell membrane (sarcolemma) along its transverse tubules. This depolarization rapidly opens voltage-gated Na+ channels (mostly NaV1.5) that further depolarize the cell membrane, allowing opening of voltage-gated Ca2+ channels (mostly CaV1.2). Inward Ca2+ current triggers opening of ryanodine receptor 2 (RyR2) channels by a Ca2+-induced Ca2+ release process, resulting in coordinated release of sarcoplasmic reticulum (SR) Ca2+ that contributes the major portion of the myofilament-activating increase in [Ca]2+i. The Ca2+ released from the SR binds to troponin C of the troponin–tropomyosin complex on the actin filaments in sarcomeres, facilitating formation of cross-bridges between actin and myosin and myocardial contraction. Voltage-gated K+ channels open to allow an outward current that favors AP repolarization, establishing conditions required for relaxation. Relaxation occurs when Ca2+ is taken back up into the SR through the action of the SR Ca2+ adenosine triphosphatase SERCA2a and is extruded from the cell by the sarcolemmal Na+ and Ca2+ exchanger (NCX). SERCA2a is constrained by phospholamban (PLN) under resting conditions. [Powerpoint File]

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Min Luo, Mark E. Anderson

Regulation of [Ca]2+i homeostasis by Ca2+-binding proteins and kinases. Regulation of Ca2+ homeostasis involves a multitude of Ca2+-binding proteins and enzymes, including Ca2+-dependent and calmodulin-dependent protein kinase II (CaMKII), protein kinase C (PKC), protein kinase A (PKA), and S100A1. CaMKII catalyzes phosphorylation of voltage-gated Ca2+ channels (mostly CaV1.2 in ventricle) to increase Ca2+ entry, catalyzes ryanodine receptor (RyR2) phosphorylation to increase Ca2+ release, catalyzes phosphorylation of voltage-gated Na+ channels (mostly NaV1.5 in ventricle) to increase subsarcolemmal [Na+]i, which decreases the driving force for Ca2+ extrusion by the Na+/Ca2+ exchanger (NCX), and catalyzes PLN phosphorylation to reduce the inhibitory activity of PLN on SERCA2a. In general, the increased phosphorylation of these proteins by CaMKII increases Ca2+ influx and storage by the sarcoplasmic reticulum (SR), which leads to increased systolic [Ca]2+i and increased rate and magnitude of force (pressure) generation and improved lusitropy. PKA is activated by β-AR agonists and catalyzes phosphorylation of the same Ca2+ regulatory proteins modified by CaMKII, but at different amino acids. Classical PKC isoforms are activated downstream to a variety of G-protein-coupled receptors and are activated by increased [Ca]2+i, leading to decreased activity of SERCA2 by phosphorylating inhibitor 1 (I-1), resulting in PLN dephosphorylation, reducing SR Ca2+ load and Ca2+ release, causing reduced contractility. S100A1 interacts with the SERCA2a/PLN complex in a Ca2+-dependent manner to augment SR Ca2+ uptake and increase SR Ca2+ content. S100A1 also directly regulates RyR2 function, stimulates ATP synthase activity, and promotes the adenosine nucleotide translocator (ANT) function to increase ATP synthesis and mitochondrial ATP efflux in cardiomyocytes. [Powerpoint File]

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Min Luo, Mark E. Anderson

Ca2+-dependent and calmodulin-dependent protein kinase II (CaMKII) and mechanisms of arrhythmia. Sustained activation of CaMKII by oxidative stress and elevated [Ca]2+i contributes to arrhythmia in heart failure by several mechanisms. CaMKII phosphorylates L-type Ca channels (CaV1.2) to increase its open probability, causing early afterdepolarizations (EADs). Increased ICa also contributes to action potential prolongation, augmented [Ca]2+i, and delayed afterdepolarizations (DADs). CaMKII phosphorylates Na+ channels (NaV1.5) and enhances the long-lasting late INa (gain of function), promoting EADs and increasing subsarcolemmal [Na+]i to favor DADs. CaMKII favors phosphorylation of ryanodine receptor (RyR2) to increase sarcoplasmic reticulum (SR) Ca2+ leak, which shifts Na+/Ca2+ exchanger (NCX) to a forward mode, causing DADs. CaMKII contributes to arrhythmogenic structural features of injured myocardium by promoting myocyte death and collagen deposition. [Powerpoint File]

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Heart Failure Compendium: Mechanisms of Altered Ca2+ Handling in Heart Failure

Min Luo, Mark E. Anderson

Structure and activation of Ca2+-dependent and calmodulin-dependent protein kinase II (CaMKII). CaMKII consists of stacked hexamers and each monomer consists of an N-terminus catalytic domain and a C-terminus association domain that flank a core regulatory domain. CaMKII is activated when [Ca]2+i binds to calmodulin, causing CaMKII to assume an active, extended conformation. Sustained binding to calcified calmodulin (Ca2+/CaM) leads to threonine 287 autophosphorylation and sustained CaMKII activation. Oxidation of paired regulatory domain methionines (281/282) also causes sustained activation of CaMKII as oxidized CaMKII resets its Ca2+ sensitivity so that lower levels of intracellular Ca2+ are required for initial activation. Thus, both threonine 287 autophosphoryation and methionine 281/282 oxidation can convert CaMKII into a constitutively active enzyme to drive myocardial disease phenotypes. [Powerpoint File]