Averaging in vitro cardiac field potential recordings obtained with microelectrode arrays

Automated feature extraction from large cardiac electrophysiological data sets

RATIONALE

A new multi-electrode array-based application for the long-term recording of action potentials from electrogenic cells makes possible exciting cardiac electrophysiology studies in health and disease. With hundreds of simultaneous electrode recordings being acquired over a period of days, the main challenge becomes achieving reliable signal identification and quantification.

OBJECTIVE

We set out to develop an algorithm capable of automatically extracting regions of high-quality action potentials from terabyte size experimental results and to map the trains of action potentials into a low-dimensional feature space for analysis.

METHODS AND RESULTS

Our automatic segmentation algorithm finds regions of acceptable action potentials in large data sets of electrophysiological readings. We use spectral methods and support vector machines to classify our readings and to extract relevant features. We are able to show that action potentials from the same cell site can be recorded over days without detrimental effects to the cell membrane. The variability between measurements 24 h apart is comparable to the natural variability of the features at a single time point.

CONCLUSIONS

Our work contributes towards a non-invasive approach for cardiomyocyte functional maturation, as well as developmental, pathological and pharmacological studies. As the human-derived cardiac model tissue has the genetic makeup of its donor, a powerful tool for individual drug toxicity screening emerges.

A Review on Biomaterials for 3D Conductive Scaffolds for Stimulating and Monitoring Cellular Activities

During the last years, scientific research in biotechnology has been reporting a considerable boost forward due to many advances marked in different technological areas. Researchers working in the field of regenerative medicine, mechanobiology and pharmacology have been constantly looking for non-invasive methods able to track tissue development, monitor biological processes and check effectiveness in treatments. The possibility to control cell cultures and quantify their products represents indeed one of the most promising and exciting hurdles. In this perspective, the use of conductive materials able to map cell activity in a three-dimensional environment represents the most interesting approach. The greatest potential of this strategy relies on the possibility to correlate measurable changes in electrical parameters with specific cell cycle events, without affecting their maturation process and considering a physiological-like setting. Up to now, several conductive materials has been identified and validated as possible solutions in scaffold development, but still few works have stressed the possibility to use conductive scaffolds for non-invasive electrical cell monitoring. In this picture, the main objective of this review was to define the state-of-the-art concerning conductive biomaterials to provide researchers with practical guidelines for developing specific applications addressing cell growth and differentiation monitoring. Therefore, a comprehensive review of all the available conductive biomaterials (polymers, carbon-based, and metals) was given in terms of their main electric characteristics and range of applications.

Chronic Unpredictable Mild Stress Causing Cardiac and Thoracic Spinal Cord Electrophysiological Abnormalities May Be Associated with Increased Cardiac Expression of Serotonin and Growth-Associated Protein-43 in Rats

BACKGROUND

The aim of this study was to investigate the potential mechanisms by which chronic unpredictable mild stress (CMS) might induce cardiovascular disease.

METHODS

Twenty male Sprague-Dawley rats (weighing 180-250 g) were divided into the CMS group (CMS for 3 weeks) and control group (n = 10/group). Sucrose solution consumption, sucrose solution preference rate, and the open field test (horizontal and vertical movements) were used to confirm the establishment of the CMS model. Heart rate was determined in Langendorff-perfused hearts, and field action potential duration (FAPD) was measured in cardiac atrial tissue, cardiac ventricular tissue, and thoracic spinal cord segments 1-5. The expressions of serotonin (5-HT) and growth-associated protein-43 (GAP-43) in cardiac ventricular tissue were analyzed using immunohistochemistry and immunofluorescence.

RESULTS

Compared with the control group, sucrose solution consumption, sucrose solution preference rate, horizontal movement, and vertical movement were significantly lower in the CMS group (P < 0.01). The CMS group exhibited significant decreases in atrial and ventricular FAPDs (P < 0.05), as well as significant increases in heart rates (P < 0.05) and T1-5 spinal cord FAPD (P < 0.01), as compared with the control group. The expressions of 5-HT and GAP-43 in cardiac ventricular tissue were significantly higher in the CMS group than in controls (P < 0.01).

CONCLUSIONS

CMS causes cardiac and T1-5 spinal cord electrophysiological abnormalities as well as increased cardiac expression of 5-HT and GAP-43, indicating that CMS could potentially increase the risk of cardiovascular disease.

Two dimensional electrophysiological characterization of human pluripotent stem cell-derived cardiomyocyte system

Stem cell-derived cardiomyocytes provide a promising tool for human developmental biology, regenerative therapies, disease modeling, and drug discovery. As human pluripotent stem cell-derived cardiomyocytes remain functionally fetal-type, close monitoring of electrophysiological maturation is critical for their further application to biology and translation. However, to date, electrophysiological analyses of stem cell-derived cardiomyocytes has largely been limited by biologically undefined factors including 3D nature of embryoid body, sera from animals, and the feeder cells isolated from mouse. Large variability in the aforementioned systems leads to uncontrollable and irreproducible results, making conclusive studies difficult. In this report, a chemically-defined differentiation regimen and a monolayer cell culture technique was combined with multielectrode arrays for accurate, real-time, and flexible measurement of electrophysiological parameters in translation-ready human cardiomyocytes. Consistent with their natural counterpart, amplitude and dV/dt_max of field potential progressively increased during the course of maturation. Monolayer culture allowed for the identification of pacemaking cells using the multielectrode array platform and thereby the estimation of conduction velocity, which gradually increased during the differentiation of cardiomyocytes. Thus, the electrophysiological maturation of the human pluripotent stem cell-derived cardiomyocytes in our system recapitulates in vivo development. This system provides a versatile biological tool to analyze human heart development, disease mechanisms, and the efficacy/toxicity of chemicals.

Study of the union method of microelectrode array and AFM for the recording of electromechanical activities in living cardiomyocytes

Electrophysiology and mechanics are two essential components in the functions of cardiomyocytes and skeletal muscle cells. The simultaneous recording of electrophysiological and mechanical activities is important for the understanding of mechanisms underlying cell functions. For example, on the one hand, mechanisms under cardiovascular drug effects will be investigated in a comprehensive way by the simultaneous recording of electrophysiological and mechanical activities. On the other hand, computational models of electromechanics provide a powerful tool for the research of cardiomyocytes. The electrical and mechanical activities are important in cardiomyocyte models. The simultaneous recording of electrophysiological and mechanical activities can provide much experimental data for the models. Therefore, an efficient method for the simultaneous recording of the electrical and mechanical data from cardiomyocytes is required for the improvement of cardiac modeling. However, as far as we know, most of the previous methods were not easy to be implemented in the electromechanical recording. For this reason, in this study, a union method of microelectrode array and atomic force microscope was proposed. With this method, the extracellular field potential and beating force of cardiomyocytes were recorded simultaneously with a low root-mean-square noise level of 11.67 μV and 60 pN. Drug tests were conducted to verify the feasibility of the experimental platform. The experimental results suggested the method would be useful for the cardiovascular drug screening and refinement of the computational cardiomyocyte models. It may be valuable for exploring the functional mechanisms of cardiomyocytes and skeletal muscle cells under physiological or pathological conditions.

Laminar ventricular myocardium on a microelectrode array-based chip

Pharmaceutical screening based on human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and multi electrode arrays (MEAs) have been proposed as a complementary method for electrophysiological safety and efficacy assessment in drug discovery and development. Contrary to animal models, these cells offer a human genetic background but, at present, fail to recapitulate the mechanical and structural properties of the native human myocardium. Here, we report that topographical cues on soft micromolded gelatin can coax hiPSC-CMs to form laminar cardiac tissues that resemble the native architecture of the heart. Importantly, using this method we were able to record tissue-level electrophysiological responses with a commercially available MEA setup. To validate this platform, we recorded cardiac field potentials at baseline and after pharmacological interventions with a β-adrenergic agonist (isoproterenol). Further, we tested the ability of our system to predict the response of laminar human cardiac tissues to a cardiotoxic pro-drug (terfenadine) and its non-cardiotoxic metabolite (fexofenadine). Finally, we integrated our platform with microfluidic components to build a heart-on-a-chip system that can be fluidically linked with other organs-on-chips in the future.

EFFECTS OF ACUTE HYPERGLYCEMIA AND INSULIN INTERVENTION ON THE SPONTANEOUS FIELD POTENTIAL OF SINOATRIAL NODE TISSUE BY USING MICROELECTRODE ARRAYS

Traditional studies on the relationship between hyperglycemia and heart diseases generally focused on the impact of chronic and long-term effect of diabetes on cardiac functions. Most of the methods were culturing myocardial cells and giving outside stimulations. However, recent studies show that acute hyperglycemia might play a significant role in spontaneous cardiac electrophysiology. In this research we applied microelectrode arrays (MEA) to record the spontaneous sinoatrial node field potentials of C57/BL6J mice and analyzed the effects of different glucose concentrations in time domain and frequency domain by using statistical method, vector maps and fast Fourier transform (FFT). Meanwhile, we studied the effects of insulin interference in the experimental process. When the concentration of the glucose solution was greater than 40 mmol/L, the spontaneous sinoatrial node field potential changed markedly. In the time domain, the amplitude decreased rapidly and the conductive characteristics were disordered. In the frequency domain, the two spectrum peaks decreased rapidly. These changes were irreversible. However, insulin preconditioning could inhibit the impact of high glucose.

MultiElec: A MATLAB Based Application for MEA Data Analysis

We present MultiElec, an open source MATLAB based application for data analysis of microelectrode array (MEA) recordings. MultiElec displays an extremely user-friendly graphic user interface (GUI) that allows the simultaneous display and analysis of voltage traces for 60 electrodes and includes functions for activation-time determination, the production of activation-time heat maps with activation time and isoline display. Furthermore, local conduction velocities are semi-automatically calculated along with their corresponding vector plots. MultiElec allows ad hoc signal suppression, enabling the user to easily and efficiently handle signal artefacts and for incomplete data sets to be analysed. Voltage traces and heat maps can be simply exported for figure production and presentation. In addition, our platform is able to produce 3D videos of signal progression over all 60 electrodes. Functions are controlled entirely by a single GUI with no need for command line input or any understanding of MATLAB code. MultiElec is open source under the terms of the GNU General Public License as published by the Free Software Foundation, version 3. Both the program and source code are available to download from http://www.cancer.manchester.ac.uk/MultiElec/.

Novel in vitro cardiovascular constructs composed of vascular-like networks and cardiomyocytes

The interaction between different cardiac cells has shown to be important for critical biological properties including cell survival, proliferation, differentiation and function. The improvement of culture conditions with different cell types and to study their effects on cardiomyocyte viability and functionality is essential. For practical applications including general toxicity testing, drug development and tissue engineering it is important to study whether co-cultures have additional advantages over cardiomyocyte monoculture. Two multicellular in vitro cardiovascular constructs devoid of added biomaterial were developed in this study. In the first construct, neonatal rat cardiomyocytes (CM) were seeded on vascular-like network formed by human umbilical vein endothelial cells (HUVEC) and human adipose stromal cells (hASC). In the second construct, CMs were seeded on vascular-like network formed by HUVECs and human foreskin fibroblasts. The ability of these two vascular-like networks to support the viability and functionality of CMs was analyzed. Different culture media compositions were evaluated to support the development of optimal cardiovascular construct. Our results demonstrate that both vascular-like networks markedly improved CM viability and functionality. In the constructs, co-localization of CMs and vascular-like networks was seen. Multicellular constructs also allowed synchronized contractility of CMs. Serum-free medium supplemented with vascular endothelial growth factor and basic fibroblast growth factor was found to provide the most optimal conditions for cardiovascular construct as an entity. In conclusion, when combining a vascular-like network with CMs, the viability and functionality of CMs was markedly improved. The results suggest that the cardiovascular constructs developed provide a promising new tool for the assessment of toxicological and safety pharmacological effects of compounds in vitro.

Cardiomyocyte MEA data analysis (CardioMDA)--a novel field potential data analysis software for pluripotent stem cell derived cardiomyocytes

Cardiac safety pharmacology requires in-vitro testing of all drug candidates before clinical trials in order to ensure they are screened for cardio-toxic effects which may result in severe arrhythmias. Micro-electrode arrays (MEA) serve as a complement to current in-vitro methods for drug safety testing. However, MEA recordings produce huge volumes of data and manual analysis forms a bottleneck for high-throughput screening. To overcome this issue, we have developed an offline, semi-automatic data analysis software, ‘Cardiomyocyte MEA Data Analysis (CardioMDA)’, equipped with correlation analysis and ensemble averaging techniques to improve the accuracy, reliability and throughput rate of analysing human pluripotent stem cell derived cardiomyocyte (CM) field potentials. With the program, true field potential and arrhythmogenic complexes can be distinguished from one another. The averaged field potential complexes, analysed using our software to determine the field potential duration, were compared with the analogous values obtained from manual analysis. The reliability of the correlation analysis algorithm, evaluated using various arrhythmogenic and morphology changing signals, revealed a mean sensitivity and specificity of 99.27% and 94.49% respectively, in determining true field potential complexes. The field potential duration of the averaged waveforms corresponded well to the manually analysed data, thus demonstrating the reliability of the software. The software has also the capability to create overlay plots for signals recorded under different drug concentrations in order to visualize and compare the magnitude of response on different ion channels as a result of drug treatment. Our novel field potential analysis platform will facilitate the analysis of CM MEA signals in semi-automated way and provide a reliable means of efficient and swift analysis for cardiomyocyte drug or disease model studies.