Sympathetic structural and electrophysiological remodeling in a rabbit model of reperfused myocardial infarction.

Chondroitin sulfate proteoglycans (CSPGs) inhibit sympathetic reinnervation in rodent hearts post myocardial infarction (MI), causing regional hypo-innervation that is associated with supersensitivity of ß-adrenergic receptors and increased arrhythmia susceptibility. To investigate the role of CSPGs and hypo-innervation in the heart of larger mammals, we used a rabbit model of reperfused MI and tested electrophysiological responses to sympathetic nerve stimulation (SNS). Innervated hearts from MI and sham rabbits were optically mapped using voltage and Ca 2+ -sensitive dyes. SNS was performed with electrical stimulation of the spinal cord and ß-adrenergic responsiveness was tested using isoproterenol. Sympathetic nerve density and CSPG expression were evaluated using immunohistochemistry. CSPGs were robustly expressed in the infarct and border zone of all MI hearts, and the presence of CSPGs was associated with reduced sympathetic nerve density in the infarct vs. remote region. Action potential duration (APD) dispersion and susceptibility to ventricular tachycardia/fibrillation (VT/VF) were increased with SNS in MI hearts but not in sham. SNS decreased APD 80 in MI but not sham hearts, while isoproterenol decreased APD 80 in both groups. Isoproterenol also shortened Ca 2+ transient duration (CaTD 80 ) in both groups but to a greater extent in MI hearts. Our data suggest sympathetic remodeling post-MI is similar between species, with CSPGs associated with sympathetic hypo-innervation. Despite a reduction in sympathetic nerve density, the infarct region of MI hearts remained responsive to both physiological SNS and isoproterenol, potentially through preserved or elevated ß-adrenergic responsiveness, which may underly increased APD dispersion and susceptibility for VT/VF. NEW & NOTEWORTHY: Here we show that CSPGs are present in the infarcts of rabbit hearts with reperfused MI, where they are associated with reduced sympathetic nerve density. Despite hypo-innervation, sympathetic responsiveness is maintained or enhanced in MI rabbit hearts, which also demonstrate increased APD dispersion and tendency for arrhythmias following sympathetic modulation. Together, this study indicates that the mechanisms of sympathetic remodeling post-MI are similar between species, with hypo-innervation likely associated with enhanced ß-adrenergic sensitivity.

The Effect of Different Factors on Poly(lactic-co-glycolic acid) Nanoparticle Properties and Drug Release Behaviors When Co-Loaded with Hydrophilic and Hydrophobic Drugs.

Poly(lactic-co-glycolic acid) nanoparticles (PLGA NPs) are versatile drug nanocarriers with a wide spectrum of applications owing to their extensive advantages, including biodegradability, non-toxic side effects, and low immunogenicity. Among the numerous nanoparticle preparation methods available for PLGA NPs (the hydrophobic polymer), one of the most extensively utilized preparations is the sonicated-emulsified solvent evaporation method, owing to its simplicity, speed, convenience, and cost-effectiveness. Nevertheless, several factors can influence the outcomes, such as the types of concentration of the surfactants and organic solvents, as well as the volume of the aqueous phase. The objective of this article is to explore the influence of these factors on the properties of PLGA NPs and their drug release behavior following encapsulation. Herein, PLGA NPs were fabricated using bovine serum albumin (BSA) as a surfactant to investigate the impact of influencing factors, including different water-soluble organic solvents such as propylene carbonate (PC), ethyl acetate (PA), and dichloromethane (DCM). Notably, the size of PLGA NPs was smaller in the EA group compared to that in the DCM group. Moreover, PLGA NPs showed excellent stability, ascribed to the presence of the BSA surfactant. Furthermore, PLGA NPs were co-loaded with varying concentrations of hydrophilic drugs (doxorubicin hydrochloride) and hydrophobic drugs (celecoxib), and exhibited pH-sensitive drug release behavior in PBS with pH 7.4 and pH 5.5.

Chronic nicotine exposure is associated with electrophysiological and sympathetic remodeling in the intact rabbit heart.

Nicotine is the primary addictive component of tobacco products. Through its actions on the heart and autonomic nervous system, nicotine exposure is associated with electrophysiological changes and increased arrhythmia susceptibility. To assess the underlying mechanisms, we treated rabbits with transdermal nicotine (NIC, 21 mg/day) or control (CT) patches for 28 days before performing dual optical mapping of transmembrane potential (RH237) and intracellular Ca2+ (Rhod-2 AM) in isolated hearts with intact sympathetic innervation. Sympathetic nerve stimulation (SNS) was performed at the first to third thoracic vertebrae, and ß-adrenergic responsiveness was additionally evaluated following norepinephrine (NE) perfusion. Baseline ex vivo heart rate (HR) and SNS stimulation threshold were higher in NIC versus CT (P = 0.004 and P = 0.003, respectively). Action potential duration alternans emerged at longer pacing cycle lengths (PCL) in NIC versus CT at baseline (P = 0.002) and during SNS (P = 0.0003), with similar results obtained for Ca2+ transient alternans. SNS shortened the PCL at which alternans emerged in CT but not in NIC hearts. NIC-exposed hearts tended to have slower and reduced HR responses to NE perfusion, but ventricular responses to NE were comparable between groups. Although fibrosis was unaltered, NIC hearts had lower sympathetic nerve density (P = 0.03) but no difference in NE content versus CT. These results suggest both sympathetic hypoinnervation of the myocardium and regional differences in ß-adrenergic responsiveness with NIC. This autonomic remodeling may contribute to the increased risk of arrhythmias associated with nicotine exposure, which may be further exacerbated with long-term use.NEW & NOTEWORTHY Here, we show that chronic nicotine exposure was associated with increased heart rate, increased susceptibility to alternans, and reduced sympathetic electrophysiological responses in the intact rabbit heart. We suggest that this was due to sympathetic hypoinnervation of the myocardium and diminished ß-adrenergic responsiveness of the sinoatrial node following nicotine treatment. Though these differences did not result in increased arrhythmia propensity in our study, we hypothesize that prolonged nicotine exposure may exacerbate this proarrhythmic remodeling.

A whale optimization algorithm based on atom-like structure differential evolution for solving engineering design problems.

The whale optimization algorithm has received much attention since its introduction due to its outstanding performance. However, like other algorithms, the whale optimization algorithm still suffers from some classical problems. To address the issues of slow convergence, low optimization precision, and susceptibility to local convergence in the whale optimization algorithm (WOA). Defining the optimization behavior of whale individuals as quantum mechanical behavior, a whale optimization algorithm based on atom-like structure differential evolution (WOAAD) is proposed. Enhancing the spiral update mechanism by introducing a sine strategy guided by the electron orbital center. Improving the random-walk foraging mechanism by applying mutation operations to both the electron orbital center and random individuals. Performing crossover operations between the newly generated individuals from the improved mechanisms and random dimensions, followed by a selection process to retain superior individuals. This accelerates algorithm convergence, enhances optimization precision, and prevents the algorithm from falling into local convergence. Finally, implementing a scouting bee strategy, where whale individuals progressively increase the number of optimization failures within a limited parameter L. When a threshold is reached, random initialization is carried out to enhance population diversity. Conducting simulation experiments to compare the improved algorithm with the whale optimization algorithm, other optimization algorithms, and other enhanced whale optimization algorithms. The experimental results indicate that the improved algorithm significantly accelerates convergence, enhances optimization precision, and prevents the algorithm from falling into local convergence. Applying the improved algorithm to five engineering design problems, the experimental results demonstrate that the improved algorithm exhibits good applicability.

Chronic nicotine exposure is associated with electrophysiological and sympathetic remodeling in the intact rabbit heart.

Nicotine is the primary addictive component in tobacco products. Through its actions on the heart and autonomic nervous system, nicotine exposure is associated with electrophysiological changes and increased arrhythmia susceptibility. However, the underlying mechanisms are unclear. To address this, we treated rabbits with transdermal nicotine (NIC, 21 mg/day) or control (CT) patches for 28 days prior to performing dual optical mapping of transmembrane potential (RH237) and intracellular Ca 2+ (Rhod-2 AM) in isolated hearts with intact sympathetic innervation. Sympathetic nerve stimulation (SNS) was performed at the 1 st - 3 rd thoracic vertebrae, and ß-adrenergic responsiveness was additionally evaluated as changes in heart rate (HR) following norepinephrine (NE) perfusion. Baseline ex vivo HR and SNS stimulation threshold were increased in NIC vs. CT ( P = 0.004 and P = 0.003 respectively). Action potential duration alternans emerged at longer pacing cycle lengths (PCL) in NIC vs. CT at baseline ( P = 0.002) and during SNS ( P = 0.0003), with similar results obtained for Ca 2+ transient alternans. SNS reduced the PCL at which alternans emerged in CT but not NIC hearts. NIC exposed hearts also tended to have slower and reduced HR responses to NE perfusion. While fibrosis was unaltered, NIC hearts had lower sympathetic nerve density ( P = 0.03) but no difference in NE content vs. CT. These results suggest both sympathetic hypo-innervation of the myocardium and diminished ß-adrenergic responsiveness with NIC. This autonomic remodeling may underlie the increased risk of arrhythmias associated with nicotine exposure, which may be further exacerbated with continued long-term usage. NEW & NOTEWORTHY: Here we show that chronic nicotine exposure was associated with increased heart rate, lower threshold for alternans and reduced sympathetic electrophysiological responses in the intact rabbit heart. We suggest that this was due to the sympathetic hypo-innervation of the myocardium and diminished ß- adrenergic responsiveness observed following nicotine treatment. Though these differences did not result in increased arrhythmia propensity in our study, we hypothesize that prolonged nicotine exposure may exacerbate this pro-arrhythmic remodeling.

Sine Cosine Algorithm for Elite Individual Collaborative Search and Its Application in Mechanical Optimization Designs.

To address the shortcomings of the sine cosine algorithm such as the low search accuracy, slow convergence speed, and easily falling into local optimality, a sine cosine algorithm for elite individual collaborative search was proposed. Firstly, tent chaotic mapping was used to initialize the population and the hyperbolic tangent function was applied non-linearly to adjust the parameters of the sine cosine algorithm, which enhanced the uniformity of population distribution and balanced the global exploration and local exploitation ability. Secondly, the search method of the sine cosine algorithm was improved by combining the search strategy of the sine cosine algorithm, the m-neighborhood locally optimal individual-guided search strategy, and the global optimal individual-guided search strategy, and, then, the three search strategies were executed alternately, which achieved collaboration, improved the convergence accuracy, and prevented the algorithm from falling into local optima. Finally, a greedy selection strategy was employed to select the best individuals for the population, which accelerated the convergence speed of the sine cosine algorithm. The simulation results illustrated that the sine cosine algorithm for elite individual collaborative search demonstrated a better optimization performance than the sine cosine algorithm, the other improved sine cosine algorithms, the other chaos-based algorithms, and other intelligent optimization algorithms. In addition, the feasibility and applicability of the sine cosine algorithm for elite individual collaborative search were further demonstrated by two mechanical optimization design experiments.

Research on an Intelligent Mining Complete System of a Fully Mechanized Mining Face in Thin Coal Seam.

The mining environment of thin coal seam working faces is generally harsh, the labor intensity is high, and the production efficiency is low. Previous studies have shown that thin coal seam mining finds it difficult to follow machines, does not have complete sets of equipment, has a low degree of automation, and has difficult system co-control, which easily causes production safety accidents. In order to effectively solve the problems existing in thin coal seam mining, Binhu Coal Mine has established intelligent fully mechanized mining and actively explored automatic coal cutting, automatic support following, and intelligent control. The combination of an SAC electro-hydraulic control system and SAP pumping station control system has been applied in 16,108 intelligent fully mechanized coal mining faces, which realizes the automatic following of underground support and the control of adjacent support, partition support, and group operation; the automatic coal cutting of the shearer is realized by editing the automatic coal-cutting state of the shearer and adjusting the automatic parameters. A centralized control center is set up, which realizes the remote control and one-button start-stop of working face equipment. Through a comparative analysis of 16,108 intelligent fully mechanized mining faces and traditional fully mechanized mining faces, it is found that intelligent fully mechanized mining faces have obvious advantages in terms of equipment maintenance, equipment operation mode, and working face efficiency, which improve the equipment and technical mining level of thin coal seam. The application of intelligent mining in Binhu Coal Mine has a great and far-reaching impact on the development of thin coal seam mining technology in China.

Study of the mechanical characteristics of coal-serial sandstone after high temperature treatment under true triaxial loading.

In this study, a series of true triaxial loading tests were carried out on coal-measure sandstone after high temperature treatment by using a self-developed true triaxial test system combined with acoustic emission (AE) monitoring, and the mass loss, deformation characteristics and loss failure mode of sandstone before and after heat treatment were systematically studied. It is found that the true triaxial mechanical properties of sandstone after high temperature treatment are closely related to temperature, and the peak strength, maximum principal strain, volume strain, minimum fracture angle and elastic modulus, which all showed bimodal changes, and 800 °C is the threshold temperature of the first four parameters. The transition temperature of the elastic modulus is 400 °C. It is found that the test results of true triaxial high temperature sandstone are in good agreement with the existing true triaxial theory and test results. The failure forms of the samples at different temperatures show inverted "Y" or inverted "N" shapes. Shear failure occurs when the temperature is below 400 °C, and shear-tension failure occurs when the temperature is above 600 °C. At the same time, it is found that the AE signal has four periods, namely the quiet period, growth period, explosion period and decline period. The number of AE events corresponds to the deviatoric stress interval well. Experimental study of the mechanical properties of sandstone under the coupling effect of high temperature and true triaxial stress has guiding significance for the parameter selection and safety evaluation of roof sandstone in underground coal gasification.

Combined Ferromagnetic Nanoparticles for Effective Periodontal Biofilm Eradication in Rat Model.

Introduction: The critical challenge for periodontitis therapy is thoroughly eliminating the dental plaque biofilm, particularly penetrating the deep periodontal tissue. Regular therapeutic strategies are insufficient to penetrate the plaque without disturbing the commensal microflora of the oral cavity. Here, we constructed a Fe3O4 magnetic nanoparticle loading minocycline (FPM NPs) to penetrate the biofilm physically and effectively eliminate periodontal biofilm. Methods: In order to penetrate and remove the biofilm effectively, Fe3O4 magnetic nanoparticles were modified with minocycline using a co-precipitation method. The particle size and dispersion of the nanoparticles were characterized by transmission electron microscopy, scanning electron microscopy, and dynamic light scattering. The antibacterial effects were examined to verify the magnetic targeting of FPM NPs. Confocal laser scanning microscopy was employed to check the effect of FPM + MF and develop the best FPM NPs treatment strategy. Additionally, the therapeutic effect of FPM NPs was investigated in periodontitis rat models. The expression of IL-1ß, IL-6, and TNF-α in periodontal tissues was measured by qRT-PCR and Western blot. Results: The multifunctional nanoparticles exhibited intense anti-biofilm activity and good biocompatibility. The magnetic forces could pull FMP NPs against the biofilm mass and kill bacteria deep in the biofilms both in vivo and in vitro. The integrity of the bacterial biofilm is disrupted under the motivation of the magnetic field, allowing for improved drug penetration and antibacterial performance. The periodontal inflammation recovered well after FPM NPs treatment in rat models. Furthermore, FPM NPs could be monitored in real-time and have magnetic targeting potentials. Conclusion: FPM NPs exhibit good chemical stability and biocompatibility. The novel nanoparticle presents a new approach for treating periodontitis and provides experimental support for using magnetic-targeted nanoparticles in clinic applications.

Experimental Study on Mechanical and Damage Evolution Characteristics of Coal during True Triaxial Cyclic Loading and Unloading.

Research on the mechanical properties and damage evolution of coal during true triaxial cyclic loading and unloading is of great significance for maintaining the long-term safety and stability of underground engineering structures in coal mines. In this paper, firstly, the deformation, strength and fracturing characteristics of coal during true triaxial loading and true triaxial cyclic loading and unloading were analyzed. Then, the residual strain characteristics, energy distribution and evolution of coal were systematically studied. Additionally, the damage evolution laws of coal during cyclic loading and unloading were quantitatively analyzed from the perspectives of residual strain and energy dissipation, respectively. The damage evolution law based on residual strain showed that when the intermediate principal stress was high, the damage to coal was directional. With the increase in cyclic load, the coal damage variables in the directions of σ1 and σ3 increased exponentially, while that in the direction of σ2 increased quadratically. The damage evolution law based on energy dissipation showed that the coal damage variable increased exponentially with the increase in cyclic load. With the increase in σ2, the increasing speed of coal damage variable decreased first and then increased. The damage variables established based on residual strain and energy dissipation can both reveal the damage deterioration mechanism of coal during true triaxial cyclic loading and unloading, which is of great theoretical and engineering significance for scientifically evaluating the stability of underground coal and rock engineering and preventing the occurrence of major geological disasters.

Developing a Novel Enamel Adhesive with Amorphous Calcium Phosphate and Silver Nanoparticles to Prevent Demineralization during Orthodontic Treatment.

During fixed orthodontic treatment, white spot lesions are prevalent issues associated with cariogenic bacteria. This study aims to construct an orthodontic adhesive containing nanoparticles of amorphous calcium phosphate-polydopamine-Ag (NPA) fillers to combat white spot lesions. The NPA fillers were prepared and characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). The biocompatibility of the fillers was evaluated. A colony counting test evaluated the antibacterial property of the fillers against Streptococcus mutans (S. mutans). NPA fillers were mixed with orthodontic adhesive (Transbond XT) at different weight ratios (0, 0.1, 0.2, 0.3, and 0.5 wt.%). The shear bond strength and antibacterial properties were then further investigated. The results showed that NPA was prepared successfully, with good antibacterial properties. The cell survival rate of all groups of fillers was higher than 70%, showing good biocompatibility. Moreover, the shear bond strength of the orthodontic adhesive with 0.2 wt.% NPA fillers was 11.89 ± 1.27 MPa, meeting the minimal clinical bond strength requirements of 7.8 MPa. Furthermore, the orthodontic adhesive resin blocks and the extract displayed good antibacterial properties, with the number of colonies decreasing significantly (p < 0.001). Taken together, we think that an orthodontic adhesive with NPA may have a good application potential for the prevention and treatment of white spot lesions.

Whole-heart multiparametric optical imaging reveals sex-dependent heterogeneity in cAMP signaling and repolarization kinetics.

Cyclic adenosine 3',5'-monophosphate (cAMP) is a key second messenger in cardiomyocytes responsible for transducing autonomic signals into downstream electrophysiological responses. Previous studies have shown intracellular heterogeneity and compartmentalization of cAMP signaling. However, whether cAMP signaling occurs heterogeneously throughout the intact heart and how this drives sex-dependent functional responses are unknown. Here, we developed and validated a novel cardiac-specific fluorescence resonance energy transfer-based cAMP reporter mouse and a combined voltage-cAMP whole-heart imaging system. We showed that in male hearts, cAMP was uniformly activated in response to pharmacological ß-adrenergic stimulation. In contrast, female hearts showed that cAMP levels decayed faster in apical versus basal regions, which was associated with nonuniform action potential changes and notable changes in the direction of repolarization. Apical phosphodiesterase (PDE) activity was higher in female versus male hearts, and PDE inhibition prevented repolarization changes in female hearts. Thus, our imaging approach revealed sex-dependent regional breakdown of cAMP and associated electrophysiological differences.

Performance Evaluation Method for Intelligent Computing Components for Space Applications.

The computational performance requirements of space payloads are constantly increasing, and the redevelopment of space-grade processors requires a significant amount of time and is costly. This study investigates performance evaluation benchmarks for processors designed for various application scenarios. It also constructs benchmark modules and typical space application benchmarks specifically tailored for the space domain. Furthermore, the study systematically evaluates and analyzes the performance of NVIDIA Jetson AGX Xavier platform and Loongson platforms to identify processors that are suitable for space missions. The experimental results of the evaluation demonstrate that Jetson AGX Xavier performs exceptionally well and consumes less power during dense computations. The Loongson platform can achieve 80% of Xavier's performance in certain parallel optimized computations, surpassing Xavier's performance at the expense of higher power consumption.

Evaluation of Thermophysical and Mechanical Properties of Sandstone Due to High-Temperature.

In this study, thermophysical and mechanical tests were conducted on sandstone samples from room temperature to 1000 °C. Based on the test results, the thermophysical properties (such as specific heat capacity, thermal conductivity, and thermal expansion coefficient) of sandstone after high-temperature treatment and the variations of mechanical properties (including peak strength, peak strain, elastic modulus, and whole stress-strain curve) with temperature were analyzed. Indeed, the deterioration law of sandstone after high-temperature treatment was also explored with the aid of a scanning electron microscope (SEM). The results show that with the increase in temperature, the specific heat capacity and thermal expansion coefficient of sandstone samples after high-temperature treatment increase first and then decrease, while the thermal conductivity gradually decreases. The range from room temperature to 1000 °C witnesses the following changes: As temperature rises, the peak strength of sandstone rises initially and falls subsequently; the elastic modulus drops; the peak strain increases at an accelerated rate. Temperature change has a significant effect on the deterioration rules of sandstone, and the increase in temperature contributes to the transition in the failure mode of sandstone from brittle failure to ductile failure. The experimental study on the thermophysical and mechanical properties of sandstone under the action of high temperature and overburden pressure has a guiding significance for the site selection and safety evaluation of UCG projects.

Enhancing the Efficiency of Mild-Temperature Photothermal Therapy for Cancer Assisting with Various Strategies.

Conventional photothermal therapy (PTT) irradiates the tumor tissues by elevating the temperature above 48 °C to exert thermal ablation, killing tumor cells. However, thermal ablation during PTT harmfully damages the surrounding normal tissues, post-treatment inflammatory responses, rapid metastasis due to the short-term mass release of tumor-cellular contents, or other side effects. To circumvent this limitation, mild-temperature photothermal therapy (MTPTT) was introduced to replace PTT as it exerts its activity at a therapeutic temperature of 42-45 °C. However, the significantly low therapeutic effect comes due to the thermoresistance of cancer cells as MTPTT figures out some of the side-effects issues. Herein, our current review suggested the mechanism and various strategies for improving the efficacy of MTPTT. Especially, heat shock proteins (HSPs) are molecular chaperones overexpressed in tumor cells and implicated in several cellular heat shock responses. Therefore, we introduced some methods to inhibit activity, reduce expression levels, and hinder the function of HSPs during MTPTT treatment. Moreover, other strategies also were emphasized, including nucleus damage, energy inhibition, and autophagy mediation. In addition, some therapies, like radiotherapy, chemotherapy, photodynamic therapy, and immunotherapy, exhibited a significant synergistic effect to assist MTPTT. Our current review provides a basis for further studies and a new approach for the clinical application of MTPTT.

Comparative Study on the Seepage Characteristics of Gas-Containing Briquette and Raw Coal in Complete Stress-Strain Process.

In this study, triaxial compression and seepage tests were conducted on briquette and raw coal samples using a coal rock mechanics-seepage triaxial test system (TAWD-2000) to obtain the complete stress-strain curves of the two samples under certain conditions. On this basis, the different damage forms of the two coal samples and the effect of their deformation and damage on their permeability were analyzed from the perspective of fine-scale damage mechanics. Moreover, the sensitivity of permeability to external variables and the suddenness of coal and gas outbursts were discussed. The results show that the compressive strength of raw coal is 27.1 MPa and the compressive strength of briquette is 17.3 MPa, the complete stress-strain curves of the two coal samples can be divided into four stages and show a good correspondence to the permeability-axial strain curves. Since briquette and raw coal have different structural properties, they present different damage mechanisms under load, thus showing great diversity in the permeability-axial strain curve, especially in the damage stage. The deformation affects the seepage characteristics of briquette mainly in the latter two stages, while it affects raw coal throughout the test. The four stages of the complete stress-strain seepage test of raw coal can well explain the four stages of coal and gas outburst process, i.e., preparation, initiation, development, and termination. Hence, the law of coal permeability to gas variation can be utilized for the coal and gas outburst prediction and forecast. The research results are valuable for exploring the real law of gas migration in coal seams.

Quantitative cross-species translators of cardiac myocyte electrophysiology: Model training, experimental validation, and applications.

Animal experimentation is key in the evaluation of cardiac efficacy and safety of novel therapeutic compounds. However, interspecies differences in the mechanisms regulating excitation-contraction coupling can limit the translation of experimental findings from animal models to human physiology and undermine the assessment of drugs' efficacy and safety. Here, we built a suite of translators for quantitatively mapping electrophysiological responses in ventricular myocytes across species. We trained these statistical operators using a broad dataset obtained by simulating populations of our biophysically detailed computational models of action potential and Ca2+ transient in mouse, rabbit, and human. We then tested our translators against experimental data describing the response to stimuli, such as ion channel block, change in beating rate, and ß-adrenergic challenge. We demonstrate that this approach is well suited to predicting the effects of perturbations across different species or experimental conditions and suggest its integration into mechanistic studies and drug development pipelines.

Role of Reduced Sarco-Endoplasmic Reticulum Ca2+-ATPase Function on Sarcoplasmic Reticulum Ca2+ Alternans in the Intact Rabbit Heart.

Sarcoplasmic reticulum (SR) Ca2+ cycling is tightly regulated by ryanodine receptor (RyR) Ca2+ release and sarco-endoplasmic reticulum Ca2+-ATPase (SERCA) Ca2+ uptake during each excitation-contraction coupling cycle. We previously showed that RyR refractoriness plays a key role in the onset of SR Ca2+ alternans in the intact rabbit heart, which contributes to arrhythmogenic action potential duration (APD) alternans. Recent studies have also implicated impaired SERCA function, a key feature of heart failure, in cardiac alternans and arrhythmias. However, the relationship between reduced SERCA function and SR Ca2+ alternans is not well understood. Simultaneous optical mapping of transmembrane potential (Vm) and SR Ca2+ was performed in isolated rabbit hearts (n = 10) using the voltage-sensitive dye RH237 and the low-affinity Ca2+ indicator Fluo-5N-AM. Alternans was induced by rapid ventricular pacing. SERCA was inhibited with cyclopiazonic acid (CPA; 1-10 µM). SERCA inhibition (1, 5, and 10 µM of CPA) resulted in dose-dependent slowing of SR Ca2+ reuptake, with the time constant (tau) increasing from 70.8 ± 3.5 ms at baseline to 85.5 ± 6.6, 129.9 ± 20.7, and 271.3 ± 37.6 ms, respectively (p < 0.05 vs. baseline for all doses). At fast pacing frequencies, CPA significantly increased the magnitude of SR Ca2+ and APD alternans, most strongly at 10 µM (pacing cycle length = 220 ms: SR Ca2+ alternans magnitude: 57.1 ± 4.7 vs. 13.4 ± 8.9 AU; APD alternans magnitude 3.8 ± 1.9 vs. 0.2 ± 0.19 AU; p < 0.05 10 µM of CPA vs. baseline for both). SERCA inhibition also promoted the emergence of spatially discordant alternans. Notably, at all CPA doses, alternation of SR Ca2+ release occurred prior to alternation of diastolic SR Ca2+ load as pacing frequency increased. Simultaneous optical mapping of SR Ca2+ and Vm in the intact rabbit heart revealed that SERCA inhibition exacerbates pacing-induced SR Ca2+ and APD alternans magnitude, particularly at fast pacing frequencies. Importantly, SR Ca2+ release alternans always occurred before the onset of SR Ca2+ load alternans. These findings suggest that even in settings of diminished SERCA function, relative refractoriness of RyR Ca2+ release governs the onset of intracellular Ca2+ alternans.

Adrenergic supersensitivity and impaired neural control of cardiac electrophysiology following regional cardiac sympathetic nerve loss.

Myocardial infarction (MI) can result in sympathetic nerve loss in the infarct region. However, the contribution of hypo-innervation to electrophysiological remodeling, independent from MI-induced ischemia and fibrosis, has not been comprehensively investigated. We present a novel mouse model of regional cardiac sympathetic hypo-innervation utilizing a targeted-toxin (dopamine beta-hydroxylase antibody conjugated to saporin, DBH-Sap), and measure resulting electrophysiological and Ca2+ handling dynamics. Five days post-surgery, sympathetic nerve density was reduced in the anterior left ventricular epicardium of DBH-Sap hearts compared to control. In Langendorff-perfused hearts, there were no differences in mean action potential duration (APD80) between groups; however, isoproterenol (ISO) significantly shortened APD80 in DBH-Sap but not control hearts, resulting in a significant increase in APD80 dispersion in the DBH-Sap group. ISO also produced spontaneous diastolic Ca2+ elevation in DBH-Sap but not control hearts. In innervated hearts, sympathetic nerve stimulation (SNS) increased heart rate to a lesser degree in DBH-Sap hearts compared to control. Additionally, SNS produced APD80 prolongation in the apex of control but not DBH-Sap hearts. These results suggest that hypo-innervated hearts have regional super-sensitivity to circulating adrenergic stimulation (ISO), while having blunted responses to SNS, providing important insight into the mechanisms of arrhythmogenesis following sympathetic nerve loss.

Aging Disrupts Normal Time-of-Day Variation in Cardiac Electrophysiology.

BACKGROUND: Cardiac gene expression and arrhythmia occurrence have time-of-day variation; however, daily changes in cardiac electrophysiology, arrhythmia susceptibility, and Ca2+ handling have not been characterized. Furthermore, how these patterns change with age is unknown. METHODS: Hearts were isolated during the light (zeitgeber time [ZT] 4 and ZT9) and dark cycle (ZT14 and ZT21) from adult (12-18 weeks) male mice. Hearts from aged (18-20 months) male mice were isolated at ZT4 and ZT14. All hearts were Langendorff-perfused for optical mapping with voltage- and Ca2+-sensitive dyes (n=4-7/group). Cardiac gene and protein expression were assessed with real-time polymerase chain reaction (n=4-6/group) and Western blot (n=3-4/group). RESULTS: Adult hearts had the shortest action potential duration (APD) and Ca2+ transient duration (CaTD) at ZT14 (APD80: ZT4: 45.4±4.1 ms; ZT9: 45.1±8.6 ms; ZT14: 34.7±4.2 ms; ZT21: 49.2±7.6 ms, P<0.05 versus ZT4 and ZT21; and CaTD80: ZT4: 70.1±3.3 ms; ZT9: 72.7±2.7 ms; ZT14: 64.3±3.3 ms; ZT21: 74.4±1.2 ms, P<0.05 versus other time points). The pacing frequency at which CaT alternans emerged was faster, and average CaT alternans magnitude was significantly reduced at ZT14 compared with the other time points. There was a trend for decreased spontaneous premature ventricular complexes and pacing-induced ventricular arrhythmias at ZT14, and the hearts at ZT14 had diminished responses to isoproterenol compared with ZT4 (ZT4: 49.5.0±5.6% versus ZT14: 22.7±9.5% decrease in APD, P<0.01). In contrast, aged hearts exhibited no difference between ZT14 and ZT4 in nearly every parameter assessed (except APD80: ZT4: 39.7±1.9 ms versus ZT14: 33.8±3.1 ms, P<0.01). Gene expression of KCNA5 (potassium voltage-gated channel subfamily A member 5; encoding Kv1.5) was increased, whereas gene expression of ADRB1 (encoding ß1-adrenergic receptors) was decreased at ZT14 versus ZT4 in adult hearts. No time-of-day changes in expression or phosphorylation of Ca2+ handling proteins (SERCA2 [sarco/endoplasmic reticulum Ca2+-ATPase], RyR2 [ryanodine receptor 2], and PLB [phospholamban]) was found in ex vivo perfused adult isolated hearts. CONCLUSIONS: Isolated adult hearts have strong time-of-day variation in cardiac electrophysiology, Ca2+ handling, and adrenergic responsiveness, which is disrupted with age.