Ephaptic coupling rescues conduction failure in weakly coupled cardiac tissue with voltage-gated gap junctions

2017 ◽  
Vol 27 (9) ◽  
pp. 093908 ◽  
Author(s):  
S. H. Weinberg
Keyword(s):  
Gap Junctions ◽  
Cardiac Tissue ◽  
Voltage Gated ◽  
Weakly Coupled ◽  
Conduction Failure ◽  
Ephaptic Coupling

scholarly journals Non-ohmic tissue conduction in cardiac electrophysiology: upscaling the non-linear voltage-dependent conductance of gap junctions

2019 ◽  
Author(s):  
Daniel E. Hurtado ◽  
Javiera Jilberto ◽  
Grigory Panasenko
Keyword(s):  
Computational Complexity ◽  
Gap Junctions ◽  
Cardiac Tissue ◽  
Tissue Level ◽  
Cardiac Conduction ◽  
Non Linear ◽  
Voltage Dependent ◽  
Junctional Coupling ◽  
Organ Level ◽  
Electrical Propagation

AbstractGap junctions are key mediators of the intercellular communication in cardiac tissue, and their function is vital to sustain normal cardiac electrical activity. Conduction through gap junctions strongly depends on the hemichannel arrangement and transjunctional voltage, rendering the intercellular conductance highly non-Ohmic. Despite this marked non-linear behavior, current tissue-level models of cardiac conduction are rooted on the assumption that gap-junctions conductance is constant (Ohmic), which results in inaccurate predictions of electrical propagation, particularly in the low junctional-coupling regime observed under pathological conditions. In this work, we present a novel non-Ohmic multiscale (NOM) model of cardiac conduction that is suitable for tissue-level simulations. Using non-linear homogenization theory, we develop a conductivity model that seamlessly upscales the voltage-dependent conductance of gap junctions, without the need of explicitly modeling gap junctions. The NOM model allows for the simulation of electrical propagation in tissue-level cardiac domains that accurately resemble that of cell-based microscopic models for a wide range of junctional coupling scenarios, recovering key conduction features at a fraction of the computational complexity. A unique feature of the NOM model is the possibility of upscaling the response of non-symmetric gap-junction conductance distributions, which result in conduction velocities that strongly depend on the direction of propagation, thus allowing to model the normal and retrograde conduction observed in certain regions of the heart. We envision that the NOM model will enable organ-level simulations that are informed by sub- and inter-cellular mechanisms, delivering an accurate and predictive in-silico tool for understanding the heart function.Author summaryThe heart relies on the propagation of electrical impulses that are mediated gap junctions, whose conduction properties vary depending on the transjunctional voltage. Despite this non-linear feature, current mathematical models assume that cardiac tissue behaves like an Ohmic (linear) material, thus delivering inaccurate results when simulated in a computer. Here we present a novel mathematical multiscale model that explicitly includes the non-Ohmic response of gap junctions in its predictions. Our results show that the proposed model recovers important conduction features modulated by gap junctions at a fraction of the computational complexity. This contribution represents an important step towards constructing computer models of a whole heart that can predict organ-level behavior in reasonable computing times.

scholarly journals Computational Approaches to Understanding the Role of Fibroblast-Myocyte Interactions in Cardiac Arrhythmogenesis

2015 ◽  
Vol 2015 ◽  
pp. 1-12 ◽  
Author(s):  
Tashalee R. Brown ◽  
Trine Krogh-Madsen ◽  
David J. Christini
Keyword(s):  
Gap Junctions ◽  
Potential Role ◽  
Cardiac Tissue ◽  
Cardiac Fibroblasts ◽  
Cardiac Arrhythmogenesis ◽  
Voltage Dependent ◽  
Underlying Mechanisms ◽  
Slow Propagation

The adult heart is composed of a dense network of cardiomyocytes surrounded by nonmyocytes, the most abundant of which are cardiac fibroblasts. Several cardiac diseases, such as myocardial infarction or dilated cardiomyopathy, are associated with an increased density of fibroblasts, that is, fibrosis. Fibroblasts play a significant role in the development of electrical and mechanical dysfunction of the heart; however the underlying mechanisms are only partially understood. One widely studied mechanism suggests that fibroblasts produce excess extracellular matrix, resulting in collagenous septa. These collagenous septa slow propagation, cause zig-zag conduction paths, and decouple cardiomyocytes resulting in a substrate for arrhythmia. Another emerging mechanism suggests that fibroblasts promote arrhythmogenesis through direct electrical interactions with cardiomyocytes via gap junctions. Due to the challenges of investigating fibroblast-myocyte coupling in native cardiac tissue, computational modeling andin vitroexperiments have facilitated the investigation into the mechanisms underlying fibroblast-mediated changes in cardiomyocyte action potential morphology, conduction velocity, spontaneous excitability, and vulnerability to reentry. In this paper, we summarize the major findings of the existing computational studies investigating the implications of fibroblast-myocyte interactions in the normal and diseased heart. We then present investigations from our group into the potential role of voltage-dependent gap junctions in fibroblast-myocyte interactions.

Simulation of the Aii amacrine cell of mammalian retina: Functional consequences of electrical coupling and regenerative membrane properties

1995 ◽  
Vol 12 (5) ◽  
pp. 851-860 ◽  
Author(s):  
Robert G. Smith ◽  
Noga Vardi
Keyword(s):  
Gap Junctions ◽  
Action Potentials ◽  
Amacrine Cell ◽  
Noise Removal ◽  
Voltage Gated ◽  
Mammalian Retina ◽  
Coupling Conductance ◽  
Slow Action Potentials ◽  
Aii Amacrine

AbstractThe Aii amacrine cell of mammalian retina collects signals from several hundred rods and is hypothesized to transmit quantal “single-photon” signals at scotopic (starlight) intensities. One problem for this theory is that the quantal signal from one rod when summed with noise from neighboring rods would be lost if some mechanism did not exist for removing the noise. Several features of the Aii might together accomplish such a noise removal operation: The Aii is interconnected into a syncytial network by gap junctions, suggesting a noise-averaging function, and a quantal signal from one rod appears in five Aii cells due to anatomical divergence. Furthermore, the Aii contains voltage-gated Na+ and K+ channels and fires slow action potentials in vitro, suggesting that it could selectively amplify quantal photon signals embedded in uncorrelated noise. To test this hypothesis, we simulated a square array of AII somas (Rm = 25,000 Ohm-cm2) interconnected by gap junctions using a compartmental model. Simulated noisy inputs to the Aii produced noise (3.5 mV) uncorrelated between adjacent cells, and a gap junction conductance of 200 pS reduced the noise by a factor of 2.5, consistent with theory. Voltage-gated Na+ and K+ channels (Na+: 4 nS, K+: 0.4 nS) produced slow action potentials similar to those found in vitro in the presence of noise. For a narrow range of Na+ and coupling conductance, quantal photon events (-5–10 mV) were amplified nonlinearly by subthreshold regenerative events in the presence of noise. A lower coupling conductance produced spurious action potentials, and a greater conductance reduced amplification. Since the presence of noise in the weakly coupled circuit readily initiates action potentials that tend to spread throughout the AII network, we speculate that this tendency might be controlled in a negative feedback loop by up-modulating coupling or other synaptic conductances in response to spiking activity.

Ouabain modulation of endothelial calcium signaling in descending vasa recta

2006 ◽  
Vol 291 (4) ◽  
pp. F761-F769 ◽  
Author(s):  
János Pittner ◽  
Kristie Rhinehart ◽  
Thomas L. Pallone
Keyword(s):  
Gap Junctions ◽  
Calcium Signaling ◽  
Calcium Concentration ◽  
Cation Channel ◽  
Cytoplasmic Calcium ◽  
Channel Blockade ◽  
Channel Activation ◽  
Voltage Gated ◽  
Vasa Recta ◽  
Peak Phase

Using fura 2-loaded vessels, we tested whether ouabain modulates endothelial cytoplasmic calcium concentration ([Ca2+]CYT) in rat descending vasa recta (DVR). Over a broad range between 10−10 and 10−4 M, ouabain elicited biphasic peak and plateau [Ca2+]CYT elevations. Blockade of voltage-gated Ca2+ entry with nifedipine did not affect the response to ouabain mitigating against a role for myo-endothelial gap junctions. Reduction of extracellular Na+ concentration ([Na+]o) or Na+/Ca2+ exchanger (NCX) inhibition with SEA-0400 (10−6 M) elevated [Ca2+]CYT, supporting a role for NCX in the setting of basal [Ca2+]CYT. SEA-0400 abolished the [Ca2+]CYT response to ouabain implicating NCX as a mediator. The transient peak phase of [Ca2+]CYT elevation that followed either ouabain or reduction of [Na+]o was abolished by 2-aminoethoxydiphenyl borate (5 × 10−5 M). Cation channel blockade with La3+ (10 μM) or SKF-96365 (10 μM) also attenuated the ouabain-induced [Ca2+]CYT response. Ouabain pretreatment increased the [Ca2+]CYT elevation elicited by bradykinin (10−7 M). We conclude that inhibition of ouabain-sensitive Na+-K+-ATPase enhances DVR endothelial Ca2+ store loading and modulates [Ca2+]CYT signaling through mechanisms that involve NCX, Ca2+ release, and cation channel activation.

scholarly journals Gap junction connexon configuration in rapidly frozen myocardium and isolated intercalated disks.

1984 ◽  
Vol 99 (2) ◽  
pp. 453-463 ◽  
Author(s):  
C R Green ◽  
N J Severs
Keyword(s):  
Gap Junctions ◽  
Gap Junction ◽  
Cardiac Tissue ◽  
Cell Biol ◽  
Junction Structure ◽  
Intercalated Disk ◽  
Hexagonal Arrays

By using two ultrarapid freezing techniques, we have captured the structure of rat and rabbit cardiac gap junctions in a condition closer to that existing in vivo than to that previously achieved. Our results, which include those from fully functional hearts frozen in situ in the living animal, show that the junctions characteristically consist of multiple small hexagonal arrays of connexons. In tissue frozen 10 min after animal death, however, unordered arrays are common. Examination of junction structure at intervals up to 40 min after death reveals a variety of configurations including dispersed and close-packed unordered arrays, and hexagonal arrays. By use of an isolated intercalated disk preparation, we show that the configuration of cardiac gap junctions in vitro cannot be altered by factors normally considered to induce functional uncoupling. These experiments demonstrate that, contrary to the conclusions of some earlier studies (Baldwin, K. M., 1979, J. Cell Biol., 82:66-75; Peracchia, C., and L. L. Peracchia, 1980, J. Cell Biol., 87:708-718), the arrangement of gap junction connexons, in cardiac tissue at least, cannot be used as a reliable guide to the functional state of the junctions.

scholarly journals Connectivity for Rapid Synchronization in a Neural Pacemaker Network

2020 ◽  
Author(s):  
Ezekiel Williams ◽  
Aaron R. Shifman ◽  
John E. Lewis
Keyword(s):  
Gap Junctions ◽  
Fundamental Property ◽  
Weakly Electric Fish ◽  
Neural Systems ◽  
Weakly Coupled ◽  
Network Properties ◽  
Brain States ◽  
Pacemaker Nucleus ◽  
Gap Junctional ◽  
Weakly Electric

AbstractSynchronization is a fundamental property of biological neural networks, playing a mechanistic role in both healthy and disease brain states. The medullary pacemaker nucleus of the weakly electric fish is a synchronized network of high-frequency neurons, weakly coupled via gap junctions. Synchrony in the pacemaker is behaviourally modulated on millisecond timescales, but how gap junctional connectivity enables such rapid resynchronization speeds is poorly understood. Here, we use a computational model of the pacemaker, along with graph theory and predictive analyses, to investigate how network properties, such as randomness and the directionality of coupling (bidirectional/non-rectifying versus directional/rectifying gap junctions) characterize the fast synchronization of the pacemaker network. Our results provide predictions about connectivity in the pacemaker and insight into the relationship between structural network properties and synchronization dynamics in neural systems more generally.

Some electrical and pharmacological properties of gap junctions between adult ventricular myocytes

1985 ◽  
Vol 249 (5) ◽  
pp. C447-C455 ◽  
Author(s):  
R. L. White ◽  
D. C. Spray ◽  
A. C. Campos de Carvalho ◽  
B. A. Wittenberg ◽  
M. V. Bennett
Keyword(s):  
Gap Junctions ◽  
Cardiac Tissue ◽  
Ventricular Myocytes ◽  
Input Resistance ◽  
Adult Rat ◽  
Junctional Communication ◽  
Cell Tissue ◽  
Physiological Properties ◽  
Rat Hearts ◽  
Junctional Conductance

Ventricular myocytes were isolated from adult rat hearts using the technique of Wittenberg and Robinson (Cell Tissue Res. 216: 231-251, 1981). These cells exhibited morphology, input resistance, time constant, and excitability expected for cells in intact cardiac tissue. Pairs of these cells were electronically coupled, and junctional conductance was unaffected by transjunctional potential or hyperpolarization of both cells. Brief exposure of cell pairs to medium equilibrated with 100% CO2 or containing 0.1 mM octanol quickly and reversibly decreased junctional conductance. We conclude that gap junctions between pairs of ventricular myocytes possess physiological properties like those of junctions in many other tissues. This preparation will be useful in evaluating drug action on junctional communication in heart.

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