A model of graded calcium release and L-type Ca2+ channel inactivation in cardiac muscle

We have developed a model of Ca2+ handling in ferret ventricular myocytes. This model includes a novel L-type Ca2+ channel, detailed intracellular Ca2+ movements, and graded Ca2+-induced Ca2+ release (CICR). The model successfully reproduces data from voltage-clamp experiments, including voltage- and time-dependent changes in intracellular Ca2+ concentration ([Ca2+]i), L-type Ca2+ channel current ( ICaL) inactivation and recovery kinetics, and Ca2+ sparks. The development of graded CICR is critically dependent on spatial heterogeneity and the physical arrangement of calcium channels in opposition to ryanodine-sensitive release channels. The model contains spatially distinct subsystems representing the subsarcolemmal regions where the junctional sarcoplasmic reticulum (SR) abuts the T-tubular membrane and where the L-type Ca2+ channels and SR ryanodine receptors (RyRs) are localized. There are eight different types of subsystems in our model, with between one and eight L-type Ca2+ channels distributed binomially. This model exhibits graded CICR and provides a quantitative description of Ca2+ dynamics not requiring Monte-Carlo simulations. Activation of RyRs and release of Ca2+ from the SR depend critically on Ca2+ entry through L-type Ca2+ channels. In turn, Ca2+ channel inactivation is critically dependent on the release of stored intracellular Ca2+. Inactivation of ICaL depends on both transmembrane voltage and local [Ca2+]i near the channel, which results in distinctive inactivation properties. The molecular mechanisms underlying many ICaL gating properties are unclear, but [Ca2+]i dynamics clearly play a fundamental role.

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BAY K 8644 modifies Ca2+cross signaling between DHP and ryanodine receptors in rat ventricular myocytes

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.276.4.h1178 ◽

1999 ◽

Vol 276 (4) ◽

pp. H1178-H1189 ◽

Cited By ~ 5

Author(s):

Satomi Adachi-Akahane ◽

Lars Cleemann ◽

Martin Morad

Keyword(s):

Amplification Factor ◽

Ventricular Myocytes ◽

Ryanodine Receptors ◽

Bay K 8644 ◽

Local Exchange ◽

Rat Ventricular Myocytes ◽

Channel Current ◽

Dependent Inactivation ◽

Intracellular Ca ◽

Kinetics Of

The amplification factor of dihydropyridine (DHP)/ryanodine receptors was defined as the amount of Ca2+ released from the sarcoplasmic reticulum (SR) relative to the influx of Ca2+ through L-type Ca2+ channels in rat ventricular myocytes. The amplification factor showed steep voltage dependence at potentials negative to −10 mV but was less dependent on voltage at potentials positive to this value. In cells dialyzed with 0.2 mM cAMP in addition to 2 mM fura 2, the Ca2+-channel agonist (−)-BAY K 8644 enhanced Ca2+-channel current ( I Ca), shifted the activation curve by −10 mV, and significantly delayed its inactivation. Surprisingly, BAY K 8644 reduced the amplification factor by 50% at all potentials, even though the caffeine-releasable Ca2+ stores were mostly intact at holding potentials of −90 mV. In contrast, brief elevation of extracellular Ca2+ activity from 2 to 10 mM enhanced both I Ca and intracellular Ca2+ transients in the absence or presence of BAY K 8644 but had no significant effect on the amplification factor. BAY K 8644 abolished the direct dependence of the rate of inactivation of I Ca on the release of Ca2+ from the SR. These findings suggest that the gain of the Ca2+-induced Ca2+ release in cardiac myocytes is regulated by the gating kinetics of cardiac L-type Ca2+ channels via local exchange of Ca2+ signals between DHP and ryanodine receptors and that BAY K 8644 suppresses the amplification factor through attenuation of the Ca2+-dependent inactivation of Ca2+ channels.

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Dual role of junctin in the regulation of ryanodine receptors and calcium release in cardiac ventricular myocytes

The Journal of Physiology ◽

10.1113/jphysiol.2011.215988 ◽

2011 ◽

Vol 589 (24) ◽

pp. 6063-6080 ◽

Cited By ~ 18

Author(s):

Beth A. Altschafl ◽

Demetrios A. Arvanitis ◽

Oscar Fuentes ◽

Qunying Yuan ◽

Evangelia G. Kranias ◽

...

Keyword(s):

Calcium Release ◽

Ventricular Myocytes ◽

Ryanodine Receptors ◽

Dual Role ◽

Cardiac Ventricular Myocytes

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Sex-related effects on diabetes-induced alterations in calcium release in the rat heart

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00619.2007 ◽

2007 ◽

Vol 293 (6) ◽

pp. H3584-H3592 ◽

Cited By ~ 21

Author(s):

Nazmi Yaras ◽

Erkan Tuncay ◽

Nuhan Purali ◽

Babur Sahinoglu ◽

Guy Vassort ◽

...

Keyword(s):

Calcium Release ◽

Binding Protein ◽

Ryanodine Receptors ◽

Left Ventricular ◽

Adult Rats ◽

Fk506 Binding Protein ◽

Pressure Development ◽

Spatiotemporal Parameters ◽

Intracellular Ca ◽

Developed Pressure

The present study was designed to determine whether the properties of local Ca2+ release and its related regulatory mechanisms might provide insight into the role of sex differences in heart functions of control and streptozotocin-induced diabetic adult rats. Left ventricular developed pressure, the rates of pressure development and decay (±dP/d t), basal intracellular Ca2+ level ([Ca2+]i), and spatiotemporal parameters of [Ca2+]i transients were found to be similar in male and female control rats. However, spatiotemporal parameters of Ca2+ sparks in cardiomyocytes isolated from control females were significantly larger and slower than those in control males. Diabetes reduced left ventricular developed pressure to a lower extent in females than in males, and the diabetes-induced depressions in both +dP/d t and −dP/d t were less in females than in males. Diabetes elicited a smaller reduction in the amplitude of [Ca2+]i transients in females than in males, a smaller reduction in sarcoplasmic reticulum-Ca2+ load, and less increase in basal [Ca2+]i. Similarly, the elementary Ca2+ events and their control proteins were clearly different in both sexes, and these differences were more marked in diabetes. Diabetes-induced depression of the Ca2+ spark amplitude was significantly less in females than in matched males. Levels of cardiac ryanodine receptors (RyR2) and FK506-binding protein 12.6 in control females were significantly higher than those shown in control males. Diabetes induced less RyR2 phosphorylation and FK506-binding protein 12.6 unbinding in females. Moreover, total and free sulfhydryl groups were significantly less reduced, and PKC levels were less increased, in diabetic females than in diabetic males. The present data related to local Ca2+ release and its related proteins describe some of the mechanisms that may underlie sex-related differences accounting for females to have less frequent development of cardiac diseases.

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Dust from hog confinement facilities impairs Ca2+ mobilization from sarco(endo)plasmic reticulum by inhibiting ryanodine receptors

Journal of Applied Physiology ◽

10.1152/japplphysiol.00661.2012 ◽

2013 ◽

Vol 114 (5) ◽

pp. 665-674

Author(s):

Chengju Tian ◽

Caronda J. Moore ◽

Puttappa Dodmane ◽

Chun Hong Shao ◽

Debra J. Romberger ◽

...

Keyword(s):

Binding Sites ◽

Molecular Mechanisms ◽

Ryanodine Receptors ◽

Cell Types ◽

C2c12 Cells ◽

Common Element ◽

Plasmic Reticulum ◽

Skeletal Muscle Weakness ◽

Intracellular Ca ◽

Phosphate Buffered Saline

Individuals working in commercial hog confinement facilities have elevated incidences of headaches, depression, nausea, skeletal muscle weakness, fatigue, gastrointestinal disorders, and cardiovascular diseases, and the molecular mechanisms for these nonrespiratory ailments remain incompletely undefined. A common element underlying these diverse pathophysiologies is perturbation of intracellular Ca2+ homeostasis. This study assessed whether the dust generated inside hog confinement facilities contains compounds that alter Ca2+ mobilization via ryanodine receptors (RyRs), key intracellular channels responsible for mobilizing Ca2+ from internal stores to elicit an array of physiologic functions. Hog barn dust (HBD) was extracted with phosphate-buffered saline, sterile-filtered (0.22 μm), and size-separated using Sephadex G-100 resin. Fractions (F) 1 through 9 (Mw >10,000 Da) had no measurable effects on RyR isoforms. However, F10 through F17, which contained compounds of Mw ≤2,000 Da, modulated the [3H]ryanodine binding to RyR1, RyR2, and RyR3 in a biphasic (Gaussian) manner. The Ki values for F13, the most potent fraction, were 3.8 ± 0.2 μg/ml for RyR1, 0.2 ± 0.01 μg/ml and 19.1 ± 2.8 μg/ml for RyR2 (two binding sites), and 44.9 ± 2.8 μg/ml and 501.6 ± 9.2 μg/ml for RyR3 (two binding sites). In lipid bilayer assays, F13 dose-dependently decreased the open probabilities of RyR1, RyR2, and RyR3. Pretreating differentiated mouse skeletal myotubes (C2C12 cells) with F13 blunted the amplitudes of ryanodine- and K+-induced Ca2+ transients. Because RyRs are present in many cell types, impairment in Ca2+ mobilization from internal stores via these channels is a possible mechanism by which HBD may trigger these seemingly unrelated pathophysiologies.

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Calcium homeostasis in a local/global whole cell model of permeabilized ventricular myocytes with a Langevin description of stochastic calcium release

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.00296.2014 ◽

2015 ◽

Vol 308 (5) ◽

pp. H510-H523 ◽

Cited By ~ 4

Author(s):

Xiao Wang ◽

Seth H. Weinberg ◽

Yan Hao ◽

Eric A. Sobie ◽

Gregory D. Smith

Keyword(s):

Calcium Release ◽

Ventricular Myocytes ◽

Cell Model ◽

Ryanodine Receptors ◽

Planck Equation ◽

Linear Increase ◽

Langevin Equations ◽

Cell Models ◽

Whole Cell ◽

Alternative Approach

Population density approaches to modeling local control of Ca2+-induced Ca2+ release in cardiac myocytes can be used to construct minimal whole cell models that accurately represent heterogeneous local Ca2+ signals. Unfortunately, the computational complexity of such “local/global” whole cell models scales with the number of Ca2+ release unit (CaRU) states, which is a rapidly increasing function of the number of ryanodine receptors (RyRs) per CaRU. Here we present an alternative approach based on a Langevin description of the collective gating of RyRs coupled by local Ca2+ concentration ([Ca2+]). The computational efficiency of this approach no longer depends on the number of RyRs per CaRU. When the RyR model is minimal, Langevin equations may be replaced by a single Fokker-Planck equation, yielding an extremely compact and efficient local/global whole cell model that reproduces and helps interpret recent experiments that investigate Ca2+ homeostasis in permeabilized ventricular myocytes. Our calculations show that elevated myoplasmic [Ca2+] promotes elevated network sarcoplasmic reticulum (SR) [Ca2+] via SR Ca2+-ATPase-mediated Ca2+ uptake. However, elevated myoplasmic [Ca2+] may also activate RyRs and promote stochastic SR Ca2+ release, which can in turn decrease SR [Ca2+]. Increasing myoplasmic [Ca2+] results in an exponential increase in spark-mediated release and a linear increase in nonspark-mediated release, consistent with recent experiments. The model exhibits two steady-state release fluxes for the same network SR [Ca2+] depending on whether myoplasmic [Ca2+] is low or high. In the later case, spontaneous release decreases SR [Ca2+] in a manner that maintains robust Ca2+ sparks.

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Akkermansia muciniphila secretome promotes α-synuclein aggregation in enteroendocrine cells

10.1101/2021.02.12.430931 ◽

2021 ◽

Author(s):

Dionísio Pedro Amorim Neto ◽

Beatriz Pelegrini Bosque ◽

João Vitor Pereira de Godoy ◽

Paulla Vieira Rodrigues ◽

Dario Donoso Meneses ◽

...

Keyword(s):

Parkinson’S Disease ◽

Parkinson's Disease ◽

Calcium Release ◽

Ryanodine Receptors ◽

Enteroendocrine Cells ◽

Ros Generation ◽

List Type ◽

Functional Link ◽

Akkermansia Muciniphila ◽

Intracellular Ca

ABSTRACTThe notion that the gut microbiota play a role in neurodevelopment, behavior and outcome of neurodegenerative disorders is recently taking place. A number of studies have consistently reported a greater abundance of Akkermansia muciniphila in Parkinson’s disease (PD) fecal samples. Nevertheless, a functional link between A.muciniphila and sporadic PD remained unexplored. Here, we investigated whether A.muciniphila secretome could initiate the misfolding process of α-synuclein (αSyn) in enteroendocrine cells (EECs), which are part of the gut epithelium and possess many neuron-like properties. We found that A.muciniphila secretome is directly modulated by mucin, induces intracellular calcium (Ca2+) release, and causes increased mitochondrial Ca2+ uptake in EECs, which in turn leads to production of reactive oxygen species (ROS) and αSyn aggregation. However, these events were efficiently inhibited once we buffered mitochondrial Ca2+. Thereby, these molecular insights provided here offer evidence that bacterial secretome is capable of inducing αSyn aggregation in enteroendocrine cells.SYNOPSIS FIGURE DESCRIPTIONThe secretome isolated from the commensal gut bacterium Akkermansia muciniphila triggers intracellular Ca2+ signaling in enteroendocrine cells, leading to increased mitochondrial Ca2+ uptake. Mitochondrial Ca2+ overload leads to ROS generation culminating with αSyn phosphorylation and aggregation (left panel). All these events were inhibited once mitochondrial Ca2+ is buffered (right panel).Gram-negative gut bacterium Akkermansia muciniphila is consistently found more abundant in Parkinson’s disease patients.Akkermansia muciniphila protein secretome composition is directly modulated by mucin and induces an IP3-independent endoplasmic reticulum (ER)-calcium release in enteroendocrine cells.This Ca2+ release is triggered by direct activation of Ryanodine Receptors leading to increased mitochondrial Ca2+ uptake.Mitochondrial Ca2+ overload leads to ROS generation culminating with αSyn aggregation.Buffering mitochondrial Ca2+ efficiently inhibits A.muciniphila-induced αSyn aggregation in enteroendocrine cells.

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

Circulation Research ◽

10.1161/circresaha.119.315715 ◽

2021 ◽

Vol 128 (1) ◽

pp. 92-114

Author(s):

Polina Gross ◽

Jaslyn Johnson ◽

Carlos M. Romero ◽

Deborah M. Eaton ◽

Claire Poulet ◽

...

Keyword(s):

Sarcoplasmic Reticulum ◽

Ventricular Myocytes ◽

Close Association ◽

Ryanodine Receptors ◽

Left Ventricular ◽

Induced Mutations ◽

Adrenergic Stimulation ◽

T Tubules ◽

Junctional Sarcoplasmic Reticulum

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

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Warmer, faster, stronger: Ca2+ cycling in avian myocardium

Journal of Experimental Biology ◽

10.1242/jeb.228205 ◽

2020 ◽

Vol 223 (19) ◽

pp. jeb228205

Author(s):

Tatiana S. Filatova ◽

Denis V. Abramochkin ◽

Holly A. Shiels

Keyword(s):

Cross Talk ◽

High Efficiency ◽

Ventricular Myocytes ◽

Contractile Function ◽

Ryanodine Receptors ◽

Atrial Cells ◽

Ventricular Cells ◽

Dependent Inactivation ◽

Intracellular Ca ◽

Mammalian Myocardium

ABSTRACTBirds occupy a unique position in the evolution of cardiac design. Their hearts are capable of cardiac performance on par with, or exceeding that of mammals, and yet the structure of their cardiomyocytes resembles those of reptiles. It has been suggested that birds use intracellular Ca2+ stored within the sarcoplasmic reticulum (SR) to power contractile function, but neither SR Ca2+ content nor the cross-talk between channels underlying Ca2+-induced Ca2+ release (CICR) have been studied in adult birds. Here we used voltage clamp to investigate the Ca2+ storage and refilling capacities of the SR and the degree of trans-sarcolemmal and intracellular Ca2+ channel interplay in freshly isolated atrial and ventricular myocytes from the heart of the Japanese quail (Coturnix japonica). A trans-sarcolemmal Ca2+ current (ICa) was detectable in both quail atrial and ventricular myocytes, and was mediated only by L-type Ca2+ channels. The peak density of ICa was larger in ventricular cells than in atrial cells, and exceeded that reported for mammalian myocardium recorded under similar conditions. Steady-state SR Ca2+ content of quail myocardium was also larger than that reported for mammals, and reached 750.6±128.2 μmol l−1 in atrial cells and 423.3±47.2 μmol l−1 in ventricular cells at 24°C. We observed SR Ca2+-dependent inactivation of ICa in ventricular myocytes, indicating cross-talk between sarcolemmal Ca2+ channels and ryanodine receptors in the SR. However, this phenomenon was not observed in atrial myocytes. Taken together, these findings help to explain the high-efficiency avian myocyte excitation–contraction coupling with regard to their reptilian-like cellular ultrastructure.

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CaM kinase augments cardiac L-type Ca2+ current: a cellular mechanism for long Q-T arrhythmias

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1999.276.6.h2168 ◽

1999 ◽

Vol 276 (6) ◽

pp. H2168-H2178 ◽

Cited By ~ 36

Author(s):

Yuejin Wu ◽

Leigh B. MacMillan ◽

R. Blair McNeill ◽

Roger J. Colbran ◽

Mark E. Anderson

Keyword(s):

Ventricular Myocytes ◽

Ryanodine Receptors ◽

Cam Kinase ◽

Early Afterdepolarizations ◽

Ultrastructural Studies ◽

Intracellular Ca ◽

Dependent Protein ◽

T Tubules ◽

Rabbit Ventricular Myocytes

Early afterdepolarizations (EAD) caused by L-type Ca2+ current ( I Ca,L) are thought to initiate long Q-T arrhythmias, but the role of intracellular Ca2+ in these arrhythmias is controversial. Rabbit ventricular myocytes were stimulated with a prolonged EAD-containing action potential-clamp waveform to investigate the role of Ca2+/calmodulin-dependent protein kinase II (CaM kinase) in I Ca,L during repolarization. I Ca,L was initially augmented, and augmentation was dependent on Ca2+ from the sarcoplasmic reticulum because the augmentation was prevented by ryanodine or thapsigargin. I Ca,Laugmentation was also dependent on CaM kinase, because it was prevented by dialysis with the inhibitor peptide AC3-I and reconstituted by exogenous constitutively active CaM kinase when Ba2+ was substituted for bath Ca2+. Ultrastructural studies confirmed that endogenous CaM kinase, L-type Ca2+ channels, and ryanodine receptors colocalized near T tubules. EAD induction was significantly reduced in current-clamped cells dialyzed with AC3-I (4/15) compared with cells dialyzed with an inactive control peptide (11/15, P = 0.013). These findings support the hypothesis that EADs are facilitated by CaM kinase.

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Abstract 14409: TRPA1 Channels Are a Source of Calcium-driven Cellular Mechano-arrhythmogenicity

Circulation ◽

10.1161/circ.142.suppl_3.14409 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Breanne A Cameron ◽

Matthew R Stoyek ◽

T Alexander Quinn

Keyword(s):

Molecular Mechanisms ◽

Sarcomere Length ◽

Fluorescent Dyes ◽

Ventricular Myocytes ◽

Cardiac Mechanics ◽

Cell Stiffness ◽

Intracellular Ca ◽

Rabbit Ventricular Myocytes ◽

Induced Changes ◽

Stretch Activated Channels

Introduction: Pathologic changes in myocardial mechanics and hemodynamic load result in arrhythmias via mechanically-induced changes in electrophysiology or intracellular Ca 2+ (‘mechano-arrhythmogenicity’). While molecular mechanisms driving mechano-arrhythmogenicity are poorly defined, they are associated with disease-related alterations in voltage-Ca 2+ dynamics. Objective: Define mechanisms of mechano-arrhythmogenicity during alterations in voltage-Ca 2+ dynamics in rabbit ventricular myocytes. Methods: Rabbit (♀, NZW) LV myocytes were transiently stretched (8-16% change in sarcomere length, 100ms) during diastole or late repolarisation in control or during K ATP channel activation (pinacidil). Drugs were used to buffer Ca 2+ (BAPTA), stabilise RyR (dantrolene), non-selectively block stretch-activated channels (streptomycin), or specifically block (HC-030031) or activate (AITC) mechano-sensitive TRPA1 channels. Voltage-Ca 2+ dynamics were simultaneously monitored with fluorescent dyes (di-4-ANBDQPQ, Fluo-5F) and a single camera-optical splitter system and diastolic Ca 2+ was measured using Fura Red. Results: Pinacidil caused greater shortening of the AP than Ca 2+ transient (-144±17 vs -74±11ms; n =24 cells, N =7 rabbits; p <0.001) with no change in cell stiffness or contractility. Stretch during pinacidil application caused arrhythmias in both diastole and late repolarisation (8 and 10% of stretches; n =46, N =5), which voltage-Ca 2+ imaging revealed were Ca 2+ -driven. Arrhythmias were reduced with BAPTA (3 and 0% of stretches; p <0.05), streptomycin (4 and 2%; p <0.05), and HC-030031(2 and 1%; p <0.01), while dantrolene had no effect ( n =40, N =5 for each). Stretch in diastole during AITC application also caused arrhythmias (15%; p <0.001), which were blocked by HC-030031 (4%; p <0.001) or BAPTA (3%; p <0.001; n =40, N =5 each). Both AITC and pinacidil caused an increase in diastolic Ca 2+ (112±29 and 78±29% of control; p<0.05), which was reduced by HC-030031 with AITC (26±24%; p <0.05), but not with pinacidil ( n =25, N =5 each). Conclusions: TRPA1 activation increases mechano-arrhythmogenicity via a Ca 2+ -driven mechanism and may represent a novel anti-arrhythmic target in pathologies involving altered cardiac mechanics.

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