Biology subjects

Tveito, A.

Publications and source records attributed to Tveito, A..

At least 19 recordsLinked to original sources

bioRxiv2026

Nanoscale numerical simulations explain apparently opposing experimental findings on ephaptic coupling

A classical study found no excitation transfer when isolated cardiomyocytes were placed side by side, whereas a recent paper reported action potential transfer in carrdiomyocytes placed end to end. We use nanoscale numerical simulations based on the full Poisson-Nernst-Planck equations to investigate whether these apparently opposing observations can be explained by the different geometrical configurations. The computations show that in the end-to-end configuration, ephaptic coupling occurs when the intercellular cleft is sufficiently narrow and a sufficiently large fraction of the sodium channels is localized at the intercalated disc. Coupling is strengthened when the sodium channels are concentrated in fewer clusters and when ionic diffusion within the cleft is reduced. Under these conditions, excitation transfer occurs on a timescale consistent with rapid cell-to-cell activation. Conduction depends biphasically on cleft width and terminates abruptly beyond a critical width. Localization of potassium channels at the intercalated disc has only a moderate effect, whereas gap junctions substantially improve conduction and reduce the relative contribution of ephaptic coupling. In the side-by-side configuration, excitation transfer does not occur under physiological conditions and requires highly flattened cells, minimal separation, and unrealistically strong sodium-channel clustering. The different outcomes of the side-by-side and end-to-end experiments can therefore be explained by the fundamentally different geometrical conditions for ephaptic coupling.

biophysics↗

bioRxiv2026

Drug Proarrhythmic Evaluation in a High Throughput Cardiac New Approach Methodology

Background and PurposeCardiotoxicity is a major cause for drug failure throughout the drug development process, with particular concern for action potential prolongation and arrhythmia. Hence, such liabilities are heavily considered during the early phases of drug design to pre vent dangerous compounds from progressing. New approach methodologies (NAMs) that efficiently examine this risk early in the discovery pipeline should help streamline drug development programs. We developed a cardiac NAM, a 384-well open bath platform consisting of cardiac tissue derived from human induced pluripotent stem cell (hiPSC)-derived cardiomyocytes, enabling high-throughput drug screening while maintaining the structural and functional complexity of 3D cardiac micromuscles. MethodsWe dramatically increased throughput without compromising physiological relevance provided by the 3D micromuscle structure. Our 384-well open bath high-throughput platform allowed evaluation of multiple compounds at a time, enabling us to study the CiPA (comprehensive in vitro proarrhythmia assay) drug panel for proarrhythmia screening. We obtained phenotypic fingerprints of all 28 compounds (9 low, 11 intermediate, and 8 high arrhythmia risk; https://cipaproject.org) in dose-escalation studies around their respective clinical concentrations. The analysis was augmented with an in silico pipeline that used phenotypic biomarkers to invert data into a mathematical model of cellular currents to infer which ion channels were affected upon drug exposure, and then trained a ML model to predict channel block. Results and ConclusionsWe found accurate detection of arrhythmic potential for most of the compounds, and the in silico model inversions were consistent with published values of compound channel block. All the high risk compounds showed action potential duration (APD) prolongation coupled with either action potential abnormalities, early afterdepolarizations (EADs), or beat cessation. For the intermediate risk group, 9 out of 11 compounds caused APD prolongation alone or in combination with EADs while 2 others showed either beat cessation or beat rate change. Augmentation of APD analysis with detailed biophysical modeling and ML tools provided meaningful insight into the mechanisms involved in APD changes. Overall, our cardiac NAM allowed for fast and relevant screening for mechanistic understanding of APD prolongation and proarrhythmic activity, at massively increased throughput compared to other 3D micromuscle models. SummaryCardiotoxicity testing is critical in drug development to prevent arrhythmogenic side effects. Current stringent regulations have greatly reduced market withdrawals; however, these strict evaluations often lead to costly late-stage failures and loss of promising candidates as false positives. We developed a cardiac new approach methodology (NAM), a 384-well open bath cardiac micromuscle platform created from hiPSC-derived cardiomyocytes, enabling high-throughput drug screening while maintaining the structural and functional complexity of 3D cardiac micromuscles. Using the comprehensive in vitro proarrhythmia assay (CiPA) drug panel, we validated the system to accurately detect proarrhythmic potential. Our assay provided phenotypic fingerprints based on mechanical and electrophysiological biomarkers. Integration with computational modeling offered insights into multi-ion channel effects (MICE). Particularly, we identified sodium channel block contributions as a significant factor for poor risk prediction based on traditional parameters. The combined experimental and computational platform can enhance early drug screening, thereby reducing late-stage failures and promoting the progression of low-risk compounds with complex electrophysiological profiles.

pharmacology and toxicology↗

bioRxiv2026

Time-step restrictions for numerical approximations of the Poisson-Nernst-Planck (PNP) equations

The Poisson-Nernst-Planck (PNP) system is an accurate model of electrodiffusion of ionic species. It is commonly used in situations where nanoscale resolution is required, for instance close to ion channels in the membranes of biological cells. The inherent stiffness of the equations has made them challenging to solve and has limited the applicability of the system. In particular, the time step required for stable solutions has typically needed to be very short (nanoseconds), which makes simulations on the time scale of an action potential (milliseconds) difficult. Recently, it has been observed that avoiding operator splitting and instead solving the concentration equations and the electrostatic equation in a coupled manner relaxes the time-step limitation considerably. However, no theoretical explanation of this observation has been provided. Here, we aim to explain why the coupled scheme allows much larger time steps. We illustrate the mechanism by considering special cases that define necessary, but not sufficient, conditions for stability. We also show that these conditions remain relevant for the fully coupled PNP model in 3D.

biophysics↗

bioRxiv2026

Accurate computation of ionic concentrations in the synaptic cleftrequires the full Poisson-Nernst-Planck (PNP) equations

The synaptic cleft between neighboring neurons is the site of neurotransmitter-mediated communication that underlies normal brain function, including learning and memory. When an action potential reaches the presynaptic terminal, released neurotransmitters cross the cleft under the combined influence of diffusion and electrical forces to activate postsynaptic receptors. Despite this, synaptic-cleft transport is commonly modeled using a pure diffusion model, neglecting electrical drift. Here, we quantify the relative contributions of diffusion and electrical terms in the Poisson-Nernst-Planck (PNP) framework and assess whether the pure diffusion approximation is adequate. We solve the full PNP system in a three-dimensional computational model of the synaptic cleft at nanometer-scale resolution, tracking five ionic species (Na+, K+, Ca2+, Cl-, Glu-) with full spatial and temporal detail. Solutions are compared directly with those of the pure diffusion (D) model. The D and PNP models produce markedly different ionic concentration fields. Analysis of ionic fluxes confirms that diffusive and electrical contributions are of comparable magnitude across all species. These discrepancies are robust across parameter variations, including the number of AMPA receptors, the amount of released glutamate, the cleft height, and the cleft diffusion coefficient, and are amplified as the number of AMPA receptors increases, the cleft becomes narrower or diffusion more restricted. The quantitative and qualitative differences between the pure D model and the full PNP model demonstrate that neglecting electrical forces in the synaptic cleft has consequences. These discrepancies are large enough to alter the predicted dynamics and biological interpretation of synaptic transmission, establishing that accurate computation of ionic concentrations in the synaptic cleft requires the full PNP equations.

biophysics↗

bioRxiv2025

Extracellular Stimulation and Ephaptic Coupling of Neurons in a Fully Coupled Finite Element-Based Extracellular-Membrane-Intracellular (EMI) Model

The extracellular potential surrounding neurons is of great importance: it is measured to interpret neural activity, it underpins ephaptic coupling between neighboring cells, and it forms the basis for external stimulation of neural tissue. These phenomena have been studied for decades, both experimentally and computationally. In computational models, variants of the classical cable equation for membrane dynamics and an electrostatic equation for the extracellular field are the most common approaches. Such formulations, however, typically decouple the governing equations and therefore neglect the biophysical coupling between the extracellular (E) space, the cell membrane (M), and the intracellular (I) space. Here, we use a finite element-based Extracellular-Membrane-Intracellular (EMI) approach that solves a fully coupled system of equations to study extracellular stimulation and ephaptic coupling of cerebellar Purkinje neurons and neocortical layer 5 pyramidal neurons. These two archetypes differ substantially in morphology, ion-channel distribution, and firing behavior, and together span a range of neuronal properties. Specifically, we assess responses to extracellular stimulation while varying the distance to the stimulation source, the amplitude, and the frequency of the external current. We also investigate ephaptic interactions between neurons, and examine how the firing pattern of one neuron can be affected by the firing pattern of a neighboring neuron, how the rate of synchronization between neighboring neurons depends on cell distance and extracellular conductivity, and finally whether a neuron can directly trigger excitation in a neighboring neuron through ephaptic coupling. The results provide quantitative insight into extracellular field-mediated neural coupling and how externally applied fields, such as those used in deep brain stimulation, interact with single-neuron biophysics.

biophysics↗

bioRxiv2025

Wave propagation enhances extracellular signal strength in small excitable tissues

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) offer new opportunities to study cardiac dynamics and drug responses. High-throughput platforms often rely on extracellular potential (EP) recordings as a proxy for transmembrane voltage, making EP signal strength critical for analysis. EPs arise from spatial inhomogeneities - either intrinsic or induced by wave propagation. Using a computational model, we show that uniform simultaneous stimulation of all cells suppresses wave propagation and results in weak signals. In contrast, localized stimulation that initiates a traveling wave generates much stronger EPs, improving the robustness of biomarker extraction from extracellular recordings.

biophysics↗

bioRxiv2025

Sometimes extracellular recordings fail for good reasons

Excitable cells are commonly studied via the extracellular potentials (EPs) they generate, which underlie signals in electroencephalography (EEG), electrocardiography (ECG), and multielectrode array (MEA) recordings. However, some excitable systems produce little or no detectable EPs, for reasons that remain poorly understood. Here we show mathematically that homogeneous excitable cells and tissues - with spatially uniform ion channel distributions and no external stimulation - are extracellularly silent even in the presence of full action potentials. Specifically, an isolated, autonomous cell with uniform membrane properties generates zero EP, independent of shape, kinetics, or model complexity. The result extends to coupled cells provided the tissue remains fully homogeneous. EPs emerge only from spatial inhomogeneities, propagating electrical waves, or applied currents. We demonstrate the physiological relevance of this principle in Purkinje neurons, where clustering of sodium channels enables ephaptic synchronization, while uniform cells remain asynchronous and undetectable extracellularly. We further show that connected human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and pancreatic {beta}-cells exhibit EPs in proportion to cellular or tissue-level heterogeneity. These findings offer a unifying explanation for the observed silence of some excitable cells and are consistent with experimental reports of strong intracellular signals accompanied by weak or absent EPs.

biophysics↗

bioRxiv2025

Reduced gap junction coupling amplifies the effects of cardiomyocyte variability and destabilizes the heartbeat

Cardiomyocytes exhibit significant cell-to-cell variability due to differences in protein expression and post-tra nslational modifications in both the cell membrane and the intracellular machinery. Resulting variability in action potential propagation and configuration have been proposed to promote arrhythmia. However, such effects may be suppressed by tight electrical coupling of cells in the healthy heart, but not during pathological conditions where gap junction function is impaired. To investigate this question, we employed a cell-based mathematical model of cardiac electrophysiology, in which we systematically modified both the properties of individual cells within the array, and inter-cellular electrical connectivity (gap junctions). Despite the inclusion of marked variation in properties between cells, we observed electrical homogeneity across the array when cells were well coupled. In contrast, lower and/or more variable gap junction connectivity resulted in nonhomogeneous action potential configuration, and irregular timing of both the depolarizing and repolarizing electrical wavefronts. Pro-arrhythmic early after-depolarizations also occurred under these conditions, linked to reopening of L-type calcium channels. These effects were effectively dampened in highly coupled cells. Nevertheless, baseline differences in calcium homeostasis were not negated by gap junction coupling, indicating a limit to which electrical connections can ho-mogenize mechanical function. There are also physical limits to electrical convergence, as we observed that action potential differences persisted at the edges and corners of the array where there are fewer electrical contacts with neighbouring cells. This finding may have implications for arrhythmic susceptibility in the border zone neighbouring an infarction. In summary, our findings underscore the critical role of intercellular coupling in maintaining cardiac stability and highlight the importance of studying cardiomyocytes within a syncytium rather than in isolation.

biophysics↗

bioRxiv2025

Electrodiffusion dynamics in the cardiomyocyte dyad at nano-scale resolution using the Poisson-Nernst-Planck (PNP) equations

During each heartbeat, a voltage wave propagates through the cardiac muscle, triggering action potentials in approximately two billion cardiomyocytes. This electrical activity ensures the coordinated contraction of the heart, which is essential for its pumping function. A key event in this process is the opening of voltage-gated calcium channels in the cell membrane, allowing calcium ions to enter the cardiac dyad and triggering a large-scale release of calcium ions from the sarcoplasmic reticulum through ryanodine receptors. This process is fundamental to cardiac function because calcium subsequently binds to troponin, initiating the conformational changes necessary for myofilament contraction. The cardiac dyad is characterized by a very small volume with steep ionic concentration gradients, which is challenging for detailed mathematical modeling. Traditionally, the dyadic calcium concentration has been approximated using spatially averaged values or modeled with reaction-diffusion equations. However, at the nanometer (nm) and nanosecond (ns) scales, such approximations may be insufficient. At this resolution, the Poisson-Nernst-Planck (PNP) system provides a detailed continuous representation of the underlying electrodiffusion dynamics. Here, we present a nano-scale computational model, representing dyad dynamics using the PNP system. Potassium, sodium, and calcium channels are incorporated in the cell membrane, along with the sodium-calcium exchanger. We demonstrate the formation of the Debye layer in the resting state and highlight how both diffusive and electrical effects are required to maintain this equilibrium. Additionally, we show that cross-species ion interactions in the dyad are electrical, and that diffusion models fail to capture this effect. Finally, we illustrate how the dyad width and diffusion coefficient influence local ionic concentrations and the timing of calcium arrival at the ryanodine receptors. These results provide new insights into the electrodiffusive properties of the dyad and clarify when solving the full PNP system is necessary for accurate modeling.

biophysics↗

bioRxiv2024

A possible path to persistent re-entry waves at the outlet of the left pulmonary vein

Atrial fibrillation (AF) is the most common form of cardiac arrhythmia, often evolving from paroxysmal episodes to persistent stages over an extended timeframe. While various factors contribute to this progression, the precise biophysical mechanisms driving it remain unclear. Here we explore how rapid firing of cardiomyocytes at the outlet of the pulmonary vein of the left atria can create a substrate for a persistent re-entry wave. This is grounded in a recently formulated mathematical model of the regulation of calcium ion channel density by intracellular calcium concentrations. According to the model, the density of membrane proteins carrying calcium ions is controlled by the intracellular calcium concentrations. In particular, if the concentration increases above a certain target level, the calcium current is weakened in order to restore the target level of calcium. During rapid pacing, the intracellular calcium concentration of the cardiomyocytes increases leading to a substantial reduction of the calcium current across the membrane of the myocytes, which again reduces the action potential duration. In a spatially resolved cell-based model of the outlet of the pulmonary vein of the left atria, we show that the reduced action potential duration can lead to re-entry. Initiated by rapid pacing, often stemming from paroxysmal AF episodes lasting several days, the reduction in calcium current is a critical factor. Our findings illustrate how such episodes can foster a conducive environment for persistent AF through electrical remodeling, characterized by diminished calcium currents. This underscores the importance of promptly addressing early AF episodes to prevent their progression to chronic stages.

biophysics↗

bioRxiv2024

Evaluating computational efforts and physiological resolution of mathematical models of cardiac tissue

Computational techniques have significantly advanced our understanding of cardiac electrophysiology, yet they have predominantly concentrated on averaged models that do not represent the intricate dynamics near individual cardiomyocytes. Recently, accurate models representing individual cells have gained popularity, enabling analysis of the electrophysiology at the micrometer level. Here, we evaluate five mathematical models to determine their computational efficiency and physiological fidelity. Our findings reveal that cell-based models introduced in recent literature offer both efficiency and precision for simulating small tissue samples (comprising thousands of cardiomy-ocytes). Conversely, the traditional bidomain model and its simplified counterpart, the monodomain model, are more appropriate for larger tissue masses (encompassing millions to billions of cardiomyocytes). For simulations requiring detailed parameter variations along individual cell membranes, the EMI model emerges as the only viable choice. This model distinctively accounts for the extracellular (E), membrane (M), and intracellular (I) spaces, providing a comprehensive framework for detailed studies. Nonetheless, the EMI models applicability to large-scale tissues is limited by its substantial computational demands for subcellular resolution.

biophysics↗

bioRxiv2023

Do calcium channel blockers applied to cardiomyocytes cause increased channel expression resulting in reduced efficacy?

In the initial hours following the application of the calcium channel blocker (CCB) nifedipine to microtissues consisting of human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs), we observe notable variations in the drugs efficacy. Here, we investigate the possibility that these temporal changes in CCB effects are associated with adaptations in the expression of calcium ion channels in cardiomyocyte membranes. To explore this, we employ a recently developed mathematical model that delineates the regulation of calcium ion channel expression by intracellular calcium concentrations. According to the model, a decline in intracellular calcium levels below a certain target level triggers an upregulation of calcium ion channels. Such an upregulation, if instigated by a CCB, would then counteract the drugs inhibitory effect on calcium currents. We assess this hypothesis using time-dependent measurements of hiPSC-CMs dynamics and by refining an existing mathematical model of myocyte action potentials incorporating the dynamic nature of the number of calcium ion channels. The revised model forecasts that the CCB-induced reduction in intracellular calcium concentrations leads to a subsequent increase in calcium ion channel expression, thereby attenuating the drugs overall efficacy. The data and fit models suggests that dynamic changes in cardiac cells in the presence of CCBs may be explainable by induced changes in protein expression, and that this may lead to challenges in understanding calcium based drug effects on the heart unless timings of applications are carefully considered.

biophysics↗

bioRxiv2022

Nano-scale solution of the Poisson-Nernst-Planck (PNP) equations in a fraction of two neighboring cells reveals the magnitude of intercellular electrochemical waves

The basic building blocks of the electrophysiology of cardiomyocytes are ion channels integrated in the cell membranes. Close to the ion channels there are very strong electrical and chemical gradients. However, these gradients extend for only a few nano-meters and are therefore commonly ignored in mathematical models. The full complexity of the dynamics is modelled by the Poisson-Nernst-Planck (PNP) equations but these equations must be solved using temporal and spatial scales of nano-seconds and nano-meters. Here we report solutions of the PNP equations in a fraction of two abuttal cells separated by a tiny extracellular space. We show that when only the potassium channels of the two cells are open, a stationary solution is reached with the well-known Debye layer close to the membranes. When the sodium channels of the left cell are opened, a very strong and brief electrochemical wave emanates from the channels. If the extracellular space is sufficiently small and the number of sodium channels is sufficiently high, the wave extends all the way over to the neighboring cell and may therefore explain cardiac conduction even at very low levels of gap junctional coupling.

biophysics↗

bioRxiv2021

Mutations change excitability and the probability of re-entry in a computational model of cardiac myocytes in the sleeve of the pulmonary vein

Atrial fibrillation (AF) is a common health problem with substantial individual and societal costs. The origin of AF has been debated for more than a century, and the precise, biophysical mechanisms that are responsible for the initiation and maintenance of the chaotic electrochemical waves that define AF, remains unclear. It is well accepted that the outlet of the pulmonary veins is the primary anatomical site of AF initiation, and that electrical isolation of these regions remains the most effective treatment for AF. Furthermore, it is well known that certain ion channel or transporter mutations can significantly increase the likelihood of AF. Here, we present a computational model capable of characterizing functionally important features of the microanatomical and electrophysiological substrate that represents the transition from the pulmonary veins (PV) to the left atrium (LA) of the human heart. This model is based on a finite element representation of every myocyte in a segment of this (PV/LA) region. Thus, it allows for investigation a mix of typical PV and LA myocytes. We use the model to investigate the likelihood of ectopic beats and re-entrant waves in a cylindrical geometry representing the transition from PV to LA. In particular, we investigate and illustrate how six different AF- associated mutations can alter the probability of ectopic beats and re-entry in this region.

biophysics↗

bioRxiv2020

Computational prediction of drug response in short QT syndrome type 1 based on measurements of compound effect in stem cell-derived cardiomyocytes

Short QT (SQT) syndrome is a genetic cardiac disorder characterized by an abbreviated QT interval of the patients electrocardiogram. The syndrome is associated with increased risk of arrhythmia and sudden cardiac death and can arise from a number of ion channel mutations. Cardiomyocytes derived from induced pluripotent stem cells generated from SQT patients (SQT hiPSC-CMs) provide promising platforms for testing pharmacological treatments directly in human cardiac cells exhibiting mutations specific for the syndrome. However, a difficulty is posed by the relative immaturity of hiPSC-CMs, with the possibility that drug effects observed in SQT hiPSC-CMs could be very different from the corresponding drug effect in vivo. In this paper, we apply a multistep computational procedure for translating measured drug effects from these cells to human QT response. This process first detects drug effects on individual ion channels based on measurements of SQT hiPSC-CMs and then uses these results to estimate the drug effects on ventricular action potentials and QT intervals of adult SQT patients. We find that the procedure is able to identify IC50 values in line with measured values for the four drugs quinidine, ivabradine, ajmaline and mexiletine. In addition, the predicted effect of quinidine on the adult QT interval is in good agreement with measured effects of quinidine for adult patients. Consequently, the computational procedure appears to be a useful tool for helping predicting adult drug responses from pure in vitro measurements of patient derived cell lines. Author summaryA number of cardiac disorders originate from genetic mutations affecting the function of ion channels populating the membrane of cardiomyocytes. One example is short QT syndrome, associated with increased risk of arrhythmias and sudden cardiac death. Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) provide a promising platform for testing potential pharmacological treatments for such disorders, as human cardiomyocytes exhibiting specific mutations can be generated and exposed to drugs in vitro. However, the electrophysiological properties of hiPSC-CMs differ significantly from those of adult native cardiomyocytes. Therefore, drug effects observed for hiPSC-CMs could possibly be very different from corresponding drug effects for adult cells in vivo. In this study, we apply a computational framework for translating drug effects observed for hiPSC-CMs derived from a short QT patient to drug effects for adult short QT cardiomyocytes. For one of the considered drugs, the effect on adult QT intervals has been measured and these measurements turn out to be in good agreement with the response estimated by the computational procedure. Thus, the computational framework shows promise for being a useful tool for predicting adult drug responses from measurements of hiPSC-CMs, allowing earlier identification of compounds to accurately treat cardiac diseases.

biophysics↗

bioRxiv2020

Identifying drug response by combining measurements of the membrane potential, the cytosolic calcium concentration, and the extracellular potential in microphysiological systems

Cardiomyocytes derived from human induced pluripotent stem cells (hiPSC-CMs) offer a new means to study and understand the human cardiac action potential, and can give key insight into how compounds may interact with important molecular pathways to destabilize the electrical function of the heart. Important features of the action potential can be readily measured using standard experimental techniques, such as the use of voltage sensitive dyes and fluorescent genetic reporters to estimate transmembrane potentials and cytosolic calcium concentrations. Using previously introduced computational procedures, such measurements can be used to estimate the current density of major ion channels present in hiPSC-CMs, and how compounds may alter their behavior. However, due to the limitations of optical recordings, resolving the sodium current remains difficult from these data. Here we show that if these optical measurements are complemented with observations of the extracellular potential using multi electrode arrays (MEAs), we can accurately estimate the current density of the sodium channels. This inversion of the sodium current relies on observation of the conduction velocity which turns out to be straightforwardly computed using measurements of extracellular waves across the electrodes. The combined data including the membrane potential, the cytosolic calcium concentration and the extracellular potential further opens up for the possibility of accurately estimating the effect of novel drugs applied to hiPSC-CMs.

bioengineering↗

bioRxiv2019

Improved computational identification of drug response using optical measurements of human stem cell derived cardiomyocytes in microphysiological systems

Cardiomyocytes derived from human induced pluripotent stem cells hold great potential for drug screening applications. However, their usefulness is limited by the relative immaturity of cells electro-physiological properties as compared to native cardiomyocytes in the adult human heart. In this work, we extend and improve on methodology to address this limitation, building on previously introduced computational procedures which predict drug effects for mature cells based on changes in optical measurements of action potentials and Ca2+ transients made in stem cell derived cardiac microtissues. This methodology quantifies ion channel changes through the inversion of data into a mathematical model, and maps this response to a mature phenotype through the assumption of functional invariance of fundamental intracellular and membrane channels during maturation.\n\nHere we utilize an updated action potential model to represent both immature and mature cells, apply an IC50-based model of dose-dependent drug effects, and introduce a continuation-based optimization algorithm for analysis of dose escalation measurements using five drugs with known effects. The improved methodology can identify drug induced changes more efficiently, and quantitate important metrics such as IC50 in line with published values. Consequently, the updated methodology is a step towards employing computational procedures to elucidate drug effects in mature cardiomyocytes for new drugs using stem cell-derived experimental tissues.

biophysics↗

bioRxiv2018

Metabolically-Driven Maturation of hiPSC-Cell Derived Heart-on-a-Chip

Human induced pluripotent stem cell derived cardiomyocytes (hiPSC-CM) are a promising in vitro tool for drug development and disease modeling, but their immature electrophysiology limits diagnostic utility. Tissue engineering approaches involving aligned 3D cultures enhance hiPSC-CM structural maturation but are insufficient to induce mature electrophysiology. We hypothesized that mimicking post-natal switching of the hearts primary ATP source from glycolysis to fatty acid oxidation could enhance electrophysiological maturation of hiPSC-CM. We combined hiPSC-CM with microfabricated culture chambers to form 3D cardiac microphysiological systems (MPS) that enhanced immediate microtissue alignment and tissue specific extracellular matrix (ECM) production. Using Robust Experimental design, we identified a maturation media that improved calcium handling in MPS derived from two genetically distinct hiPSC sources. Although calcium handling and metabolic maturation were improved in both genotypes, there was a divergent effect on action potential duration (APD): MPS that started with abnormally prolonged APD exhibited shorter APD in response to maturation media, whereas the same media prolonged the APD in MPS that started with aberrantly short APD. Importantly, the APD of both genotypes was brought near the range of 270-300ms observed in human left ventricular cardiomyocytes. Mathematical modeling explained these divergent phenotypes, and further predicted the response of matured MPS to drugs with known pro-arrhythmic effects. These results suggest that systematic combination of biophysical stimuli and metabolic cues can enhance the electrophysiological maturation of hiPSC-derived cardiomyocytes. However, they also reveal that maturation-inducing cues can have differential effects on electrophysiology depending on the baseline phenotype of hiPSC-CM. In silico models provide a valuable tool for predicting how changes in cellular maturation will manifest in drug responsiveness.

bioengineering↗