Virtual cardiac monolayers for electrical wave propagation

The complex structure of cardiac tissue is considered to be one of the main determinants of an arrhythmogenic substrate. This study is aimed at developing the first mathematical model to describe the formation of cardiac tissue, using a joint in silico-in vitro approach. First, we performed experiments under various conditions to carefully characterise the morphology of cardiac tissue in a culture of neonatal rat ventricular cells. We considered two cell types, namely, cardiomyocytes and fibroblasts. Next, we proposed a mathematical model, based on the Glazier-Graner-Hogeweg model, which is widely used in tissue growth studies. The resultant tissue morphology was coupled to the detailed electrophysiological Korhonen-Majumder model for neonatal rat ventricular cardiomyocytes, in order to study wave propagation. The simulated waves had the same anisotropy ratio and wavefront complexity as those in the experiment. Thus, we conclude that our approach allows us to reproduce the morphological and physiological properties of cardiac tissue

Photocontrol of Voltage-Gated Ion Channel Activity by Azobenzene Trimethylammonium Bromide in Neonatal Rat Cardiomyocytes

<div><p>The ability of azobenzene trimethylammonium bromide (azoTAB) to sensitize cardiac tissue excitability to light was recently reported. The dark, thermally relaxed <i>trans</i>- isomer of azoTAB suppressed spontaneous activity and excitation propagation speed, whereas the <i>cis</i>- isomer had no detectable effect on the electrical properties of cardiomyocyte monolayers. As the membrane potential of cardiac cells is mainly controlled by activity of voltage-gated ion channels, this study examined whether the sensitization effect of azoTAB was exerted primarily via the modulation of voltage-gated ion channel activity. The effects of <i>trans</i>- and <i>cis</i>- isomers of azoTAB on voltage-dependent sodium (INav), calcium (ICav), and potassium (IKv) currents in isolated neonatal rat cardiomyocytes were investigated using the whole-cell patch-clamp technique. The experiments showed that azoTAB modulated ion currents, causing suppression of sodium (Na⁺) and calcium (Ca²⁺) currents and potentiation of net potassium (K⁺) currents. This finding confirms that azoTAB-effect on cardiac tissue excitability do indeed result from modulation of voltage-gated ion channels responsible for action potential.</p></div

Effect of azobenzene trimethylammonium bromide (azoTAB) on ramp currents in neonatal rat ventricular myocytes.

<p>(A) A representative TTX-sensitive current that was evoked when the voltage was increased smoothly from -120 to +50 mV for 200 ms. The cell was prepulsed to -120 mV for 100 ms from a HP of -80mV. The voltage protocol is shown above the current trace. The inset shows scaled current traces for comparison before and after the addition of 10 μM TTX. Similar results were obtained in three other cells. (B) Scaled ramp-evoked currents recorded in response to the same ramp protocol (from -120 to +50 mV, 200 ms) in the control and after the addition of 100 μM <i>trans</i>- azoTAB. Currents were recorded every 15 s after the application of the photoreactive substance. Three minutes after the application, the current was inhibited by approximately 83% relative to that of the control. Similar results were obtained in three other cells. (C) Ion currents recorded before and after incubation with 100 μM <i>trans</i>-azoTAB, as well as after near-ultraviolet (near-UV) irradiation and expressed as percentage. Each cardiomyocyte was incubated in the presence of azoTAB at room temperature for at least 3 min in a measuring chamber. Near-UV was applied for 90 s. The data represent the means ± SEM from four cardiomyocytes, *<i>p<</i> 0.05.</p

Effect of azoTAB on voltage-dependent Na⁺ currents in neonatal rat ventricular myocytes.

<p>(A) Current-voltage relationships recorded from single neonatal ventricular cardiomyocytes under control conditions (filled circles) and after exposure to 100 μM <i>trans</i>-azoTAB (open circles). Inset: the shape of the current-voltage stimulation protocol. The current density was calculated as the Na⁺ peak current divided by the membrane capacitance of each cell (<i>n</i> = 4). (B) Concentration dependency for <i>trans</i>- azoTAB-induced inhibition of INav in neonatal rat ventricular cardiomyocytes. Mean ± SEM, <i>n</i> = 3–4 for each point.</p

Effect of azoTAB on voltage-dependent Ca²⁺ currents in neonatal rat ventricular cardiomyocytes.

<p>(A) L-type Ca²⁺ currents obtained in the absence (control) and presence of 100 μM <i>trans</i>- azoTAB and after ~365 nm near-UV irradiation. Inset: original current trace in response to a voltage step from -40 to 0 mV for 300 ms. Inactivation of INav was achieved by a prestep from a holding potential HP of -80 mV to -40 mV for 100 ms. Similar results were obtained in three other cells. (B) ICavpeak recorded before and after incubation with 100 μM azoTAB, as well as after near-UV irradiation, and expressed as a percentage of that of the peak currents before the treatment. Each cardiomyocyte was incubated in the presence of azoTAB at room temperature for ~3 min in a measuring chamber. The currents were inhibited by approximately 60% relative to the control. Near-UV was applied for 90 s. The data are the means ± SEM from three cardiomyocytes, *<i>p</i>< 0.05. (C) Averaged I/V relations of the L-type Ca²⁺ currents elicited by the voltage-clamp protocol illustrated in the inset (HP = -80 mV) and plotted before (filled circles) and after (open circles) the application of azoTAB. The values are expressed as the mean ± SEM, <i>n</i> = 4. The current density is plotted as a function of the voltage.</p

Novel Molecular Vehicle-Based Approach for Cardiac Cell Transplantation Leads to Rapid Electromechanical Graft–Host Coupling

Myocardial remodeling is an inevitable risk factor for cardiac arrhythmias and can potentially be corrected with cell therapy. Although the generation of cardiac cells ex vivo is possible, specific approaches to cell replacement therapy remain unclear. On the one hand, adhesive myocyte cells must be viable and conjugated with the electromechanical syncytium of the recipient tissue, which is unattainable without an external scaffold substrate. On the other hand, the outer scaffold may hinder cell delivery, for example, making intramyocardial injection difficult. To resolve this contradiction, we developed molecular vehicles that combine a wrapped (rather than outer) polymer scaffold that is enveloped by the cell and provides excitability restoration (lost when cells were harvested) before engraftment. It also provides a coating with human fibronectin, which initiates the process of graft adhesion into the recipient tissue and can carry fluorescent markers for the external control of the non-invasive cell position. In this work, we used a type of scaffold that allowed us to use the advantages of a scaffold-free cell suspension for cell delivery. Fragmented nanofibers (0.85 µm ± 0.18 µm in diameter) with fluorescent labels were used, with solitary cells seeded on them. Cell implantation experiments were performed in vivo. The proposed molecular vehicles made it possible to establish rapid (30 min) electromechanical contact between excitable grafts and the recipient heart. Excitable grafts were visualized with optical mapping on a rat heart with Langendorff perfusion at a 0.72 ± 0.32 Hz heart rate. Thus, the pre-restored grafts’ excitability (with the help of a wrapped polymer scaffold) allowed rapid electromechanical coupling with the recipient tissue. This information could provide a basis for the reduction of engraftment arrhythmias in the first days after cell therapy