computer modeling; ion currents; cardiac cell cultures; cardiac conduction; conduction velocity; ephaptic conduction; action potential; mechano-electrical coupling; conduction block; conduction stability; cardiac arrhythmias; stretchable microelectrode arrays; gap junctions; sodium channels
Buccarello A., Azzarito M., Michoud F., Lacour S. P., Kucera J. P. (2018), Uniaxial strain of cultured mouse and rat cardiomyocyte strands slows conduction more when its axis is parallel to impulse propagation than when it is perpendicular, in Acta Physiologica
, 223(1), e13026-e13026.
Hichri Echrak, Abriel Hugues, Kucera Jan P. (2018), Distribution of cardiac sodium channels in clusters potentiates ephaptic interactions in the intercalated disc, in The Journal of Physiology
, 596(4), 563-589.
Kucera Jan P., Rohr Stephan, Kleber Andre G. (2017), Microstructure, Cell-to-Cell Coupling, and Ion Currents as Determinants of Electrical Propagation and Arrhythmogenesis, in CIRCULATION-ARRHYTHMIA AND ELECTROPHYSIOLOGY
, 10(9), e004665.
Buccarello A., Azzarito M., Michoud F., Lacour S. P., Kucera J. P. (2017), Uniaxial strain of cardiac tissue parallel to impulse propagation slows conduction more than in the perpendicular direction: untangling the effects of stretch on tissue resistance, in ACTA PHYSIOLOGICA
, 221(S713), 115-115.
Hichri Echrak, Abriel Hugues, Kucera Jan P. (2017), Ephaptic Effects Potentiate the Threshold Behavior of the Cardiac Sodium Current in a High Resolution Mathematical Model of a Narrow Intercellular Cleft, in BIOPHYSICAL JOURNAL
, 112(3), 241-242.
Jousset Florian, Maguy Ange, Rohr Stephan, Kucera Jan P. (2016), Myofibroblasts Electrotonically Coupled to Cardiomyocytes Alter Conduction: Insights at the Cellular Level from a Detailed In silico Tissue Structure Model, in FRONTIERS IN PHYSIOLOGY
, 7, 496.
Azzarito M., Prudat Y., Marcu I. C., Kucera J. P., Ullrich N. D. (2016), Reduced excitability and intercellular coupling lead to slow conduction in cultures of stem cell-derived cardiomyocytes, in ACTA PHYSIOLOGICA
, 216, 217-218.
Kucera Jan P., Prudat Yann, Marcu Irene C., Azzarito Michela, Ullrich Nina D. (2015), Slow conduction in mixed cultured strands of primary ventricular cells and stem cell-derived cardiomyocytes, in Frontiers in Cell and Developmental Biology
, 3, 58.
Heart disease is a major cause of mortality and morbidity. Heart rhythm disorders are frequently and intricately associated with heart disease. Arrhythmias can potentiate heart failure, lead to stroke and cause sudden death. Notwithstanding decades of progress in understanding arrhythmias in clinical practice and basic science, various aspects in this field still require deeper knowledge. In this proposal, we intend to explore two such aspects: A) the interaction between bioelectricity and biomechanics in the generation of arrhythmogenic mechanisms of cardiac tissue excitation and B) ephaptic impulse propagation, an alternate and still controversial mechanism by which cardiac electrical excitation is transmitted from one cell to the next.In these two projects, we will continue combining experimental approaches and computer modeling of cardiac bioelectrical phenomena. This dual approach represents our expertise that we have built over the last 15 years, and the proposed projects are founded on our accomplishments during this period.Project A:How does mechanical deformation affect action potential propagation in cardiac tissue?Cardiac conduction depends on transmembrane and gap junctional currents. However, conduction can also be modulated by deformation of cardiac tissue, especially if excitation and mechanical activity are mismatched, which may occur during heart disease and arrhythmias. Tissue deformation can affect conduction directly by changing the electrical tissue resistance or indirectly via stretch-activated channels or further mechanisms (mechano-electrical coupling).Our aim is to develop a new experimental system permitting the application of controlled deformations to cultures of cardiac cells while recording their electrical activity. We will use a new generation of stretchable microelectrode arrays (collaboration with Prof. Lacour) on which we will grow patterned cultures of rat or mice ventricular myocytes.In a first step, we will characterize the effects of fundamental deformations (uniaxial strain in the directions parallel and perpendicular to impulse propagation) on conduction characteristics. Our principal hypothesis is that strain applied in the direction of impulse propagation vs. strain perpendicular to impulse propagation permits to untangle the effects of changes in tissue resistance from the effects resulting from stretch activated currents and modifications of ion channel function. In a second step, we will investigate the underlying mechanisms (tissue resistance, stretch activated currents in myocytes or fibroblasts, mechanosensitivity of ion currents) using pharmacological interventions and genetic modifications (cells from wild-type vs. connexin 43 knockout mice).These experiments will be paralleled with computer simulations of conduction using a detailed model of tissue architecture incorporating mechanical features, including contractile force generation. This will provide a full picture of the bidirectional interactions between excitation and contraction. Our hypothesis is that microscopic heterogeneities arising from the arrangement of cells, the composition of the tissue (e.g., randomly distributed fibroblasts) and the natural variability of cellular properties lead to sites where conduction is altered more strongly by strain or even blocks.This study is expected to further our understanding of the interactions between electrophysiology and mechanics. This understanding is important to devise more efficient treatments of heart disease and a better prevention of arrhythmias.Project B:Ephaptic conduction in cardiac tissue: myth or practical reality?It is widely accepted that cardiac impulse propagation relies on the flow of current through gap junctions that electrically connect adjacent myocytes. However, an alternate mechanism has been proposed for impulse propagation, especially in situations in which gap junctional coupling is decreased. This mechanism, called “ephaptic transmission”, resides in the fact that the Na+ current through the membrane on one side of a narrow intercellular cleft (e.g., an intercalated disc) causes a negative extracellular potential within the cleft, which translates, on the other side of the cleft, into membrane depolarization and subsequent activation of Na+ channels in the neighbor cell. This mechanism is supported by simulation studies, but, to date, clear experimental evidence at the cellular level is missing. Cardiac ephaptic conduction is therefore a topic of active scientific debate.Our goal is to conduct such proof-of-principle experiments in cell pairs using mammalian cultured cells transfected with different combinations of Na+ and K+ channels that will be apposed to each other while monitoring their electrical activity using patch clamp (collaboration with Prof. Abriel). These experiments will be complemented by corresponding simulations, which will guide us in the interpretation of the experimental results.Because nothing is known about phenomena that may further determine ephaptic interactions within intercellular clefts, we will also develop a computer model of the intercellular cleft / intercalated disc incorporating increasing levels of structural detail in order to examine how ephaptic interactions are modulated by microscopic structural features within a cleft (e.g., non-uniform distribution of gap junctions and Na+ channels, perinexus regions, cleft tortuosity).This study will contribute to resolve the controversy whether ephaptic conduction can really take place in cardiac tissue, a fact which would have profound repercussions on our fundamental understanding of cardiac electrophysiology and the function of cardiac Na+ channels.