Confocal microscopy-based estimation of intracellular conductivities in myocardium for modeling of the normal and infarcted heart

Graphene SU-8 Platform for Enhanced Cardiomyocyte Maturation and Intercellular Communication in Cardiac Drug Screening

Cell culture substrates designed for myocardial applications are pivotal in promoting the maturation and functional integration of cardiomyocytes. However, traditional in vitro models often inadequately mimic the diverse biochemical signals and electrophysiological properties of mature cardiomyocytes. Herein, we propose the application of monolayer graphene, transferred onto SU-8 cantilevers integrated with a microelectrode array, to evaluate its influence on the structural, functional, and electro-mechano-physiological properties of cardiomyocytes. The monolayer graphene, prepared using chemical vapor deposition, is adeptly transferred to the target substrates via thermal release tape. The electrical conductivity of these graphene-enhanced SU-8 substrates is about 1600 S/cm, markedly surpassing that of previously reported cell culture substrates. Immunofluorescence staining and Western blot analyses reveal that the electrically conductive graphene significantly enhances cardiomyocyte maturation and cardiac marker expression compared to bare SU-8 substrates. Cardiomyocytes cultured on graphene-transferred substrates exhibit conduction velocity approximately 3.4 times greater than that of the control group. Such improvements in cardiac marker expression, mechano-electrophysiological performance lead to better responsiveness to cardiovascular drugs, such as Verapamil and Isoproterenol. While the graphene monolayer does not fully replicate the complex environment found in native cardiac tissue, its use on SU-8 substrates offers a feasible approach for accelerating cardiomyocyte maturation and facilitating drug screening applications.

Progress of Conductivity and Conduction Velocity Measured in Human and Animal Hearts

Cardiac conduction velocity (CV) is a critical electrophysiological characteristic of the myocardium, representing the speed at which electrical pulses propagate through cardiac tissue. It can be delineated into longitudinal, transverse, and normal components in the myocardium. The CV and its anisotropy ratio are crucial to both normal electrical conduction and myocardial contraction, as well as pathological conditions where it increases the risk of conduction block and reentry. This comprehensive review synthesizes longitudinal and transverse CV values from clinical and experimental studies of human infarct hearts, including findings from the isthmus and outer loop, alongside data derived from animal models. Additionally, we explore the anisotropic ratio of conductivities assessed through both animal and computational models. The review culminates with a synthesis of scientific evidence that guides the selection of CV and its corresponding conductivity in cardiac modeling, particularly emphasizing its application in patient-specific cardiac arrhythmia modeling.

Effects of electro-mechanical uncouplers, hormonal stimulation and pacing rate on the stability and function of cultured rabbit myocardial slices

Introduction: Recent advances have enabled organotypic culture of beating human myocardial slices that are stable for weeks. However, human myocardial samples are rare, exhibit high variability and frequently originate from diseased hearts. Thus, there is a need to adapt long-term slice culture for animal myocardium. When applied to animal cardiac slices, studies in healthy or genetically modified myocardium will be possible. We present the culture of slices from rabbit hearts, which resemble the human heart in microstructure, electrophysiology and excitation-contraction coupling. Methods: Left ventricular myocardium from New Zealand White rabbits was cut using a vibratome and cultured in biomimetic chambers for up to 7 days (d). Electro-mechanical uncoupling agents 2,3-butanedione monoxime (BDM) and cytochalasin D (CytoD) were added during initiation of culture and effects on myocyte survival were quantified. We investigated pacing rates (0.5 Hz, 1 Hz, and 2 Hz) and hormonal supplements (cortisol, T3, catecholamines) at physiological plasma concentrations. T3 was buffered using BSA. Contractile force was recorded continuously. Glucose consumption and lactate production were measured. Whole-slice Ca2+ transients and action potentials were recorded. Effects of culture on microstructure were investigated with confocal microscopy and image analysis. Results: Protocols for human myocardial culture resulted in sustained contracture and myocyte death in rabbit slices within 24 h, which could be prevented by transient application of a combination of BDM and CytoD. Cortisol stabilized contraction amplitude and kinetics in culture. T3 and catecholaminergic stimulation did not further improve stability. T3 and higher pacing rates increased metabolic rate and lactate production. T3 stabilized the response to β-adrenergic stimulation over 7 d. Pacing rates above 1 Hz resulted in progredient decline in contraction force. Image analysis revealed no changes in volume fractions of cardiomyocytes or measures of fibrosis over 7 d. Ca2+ transient amplitudes and responsiveness to isoprenaline were comparable after 1 d and 7 d, while Ca2+ transient duration was prolonged after 7 d in culture. Conclusions: A workflow for rabbit myocardial culture has been established, preserving function for up to 7 d. This research underscores the importance of glucocorticoid signaling in maintaining tissue function and extending culture duration. Furthermore, BDM and CytoD appear to protect from tissue damage during the initiation phase of tissue culture.

Recent progress of second near-infrared (NIR-II) fluorescence microscopy in bioimaging

Visualizing biological tissues in vivo at a cellular or subcellular resolution to explore molecular signaling and cell behaviors is a crucial direction for research into biological processes. In vivo imaging can provide quantitative and dynamic visualization/mapping in biology and immunology. New microscopy techniques combined with near-infrared region fluorophores provide additional avenues for further progress in vivo bioimaging. Based on the development of chemical materials and physical optoelectronics, new NIR-II microscopy techniques are emerging, such as confocal and multiphoton microscopy, light-sheet fluorescence microscopy (LSFM), and wide-field microscopy. In this review, we introduce the characteristics of in vivo imaging using NIR-II fluorescence microscopy. We also cover the recent advances in NIR-II fluorescence microscopy techniques in bioimaging and the potential for overcoming current challenges.