Changes In Contractility Research Articles

Diagnosis of atrial cardiomyopathy: from the electrocardiogram to the new opportunities with multimodality imaging.

Atrial cardiomyopathy (AC) has been defined by the European Heart Rhythm Association as "Any complex of structural, architectural, contractile, or electrophysiologic changes in the atria with the potential to produce clinically relevant manifestations".1 The left atrium (LA) plays a key role in maintaining normal cardiac function; in fact atrial dysfunction has emerged as an essential determinant of outcomes in different clinical scenarios, such as valvular diseases, heart failure (HF), coronary artery disease (CAD) and atrial fibrillation (AF). A comprehensive evaluation, both anatomical and functional, is routinely performed in cardiac imaging laboratories. Recent advances in imaging techniques offer opportunities for evaluation of LA function, fundamental in clinical practice for early cardiovascular (CV) risk estimation, choice of therapeutic intervention and follow up. In this review we explore the concept of AC, its diagnosis through a multimodal approach, ranging from the historical electrocardiogram to the latest CV imaging techniques and its clinical implications.

Enhanced vascular contraction induced by exposure to angiotensin II mediated by endothelin-1 biosynthesis following PKCβ activation.

Protein kinase C (PKC) reportedly plays a role in the pathogenesis of many vascular dysfunction-related conditions. In this study, we investigated whether PKCβ is associated with vascular contractile changes induced by angiotensin II (Ang II) exposure. Long-term (24 h) treatment of rat aortae and mesenteric arteries in Ang II-containing culture medium enhanced 5-hydroxytrypatamine (5-HT)-induced vascular contraction in a dose-dependent manner, in association with enhanced phosphorylation of PKCβ S660. Increased contraction induced by Ang II treatment was also observed in endothelium-denuded aorta. Enhanced contraction induced by Ang II was markedly diminished by knockout of the PKCβ gene or treatment with LY333531 and CGP53353 (PKCβ inhibitors). Cycloheximide (protein synthesis inhibitor) blocked the Ang II-induced enhanced contraction. Gene expression profiling and real-time PCR analyses showed marked upregulation of endothelin-1 (ET-1) expression in Ang II-treated aorta, but was not observed in PKCβ-knockout aorta. Ang II increased the secretion of ET-1 peptide in endothelium-intact and -denuded aortae. Ang II-induced enhancement of vascular contraction was diminished by BQ-123 (ETAR blocker). In vivo treatment with Ang II (250 ng/kg/min) for 7 days increased phosphorylation of PKCβ S660 in rat vascular tissue and increased the in vitro contractile responses to 5-HT and in vivo systolic blood pressure, but these changes were largely absent in PKCβ-knockout experiments. These data suggest that long-term exposure to Ang II increases vascular smooth muscle contraction and blood pressure elevation, mediated by activation of PKCβ and subsequent biosynthesis of ET-1 in vascular smooth muscle cells.

Pressure-volume analysis by three-dimensional echocardiography: an accurate non-invasive alternative for assessing left ventricular contractility

Abstract Introduction Accurately assessing left ventricular (LV) contractility is vital for diagnosing and managing cardiac conditions like heart failure, cardiomyopathies, and ischemic heart disease. LV contractility assessment by traditional invasive pressure-volume (PV) analysis necessitates invasive measurements, introducing significant risks and limitations. However, three-dimensional (3D) echocardiography and non-invasive LV pressure curve estimation enables accurate PV-loop estimation, presenting a harmless and widely available alternative for LV contractility assessment. Aim Validate indices of LV contractility by PV analysis using 3D echocardiography by comparing them to gold-standard invasive measurements. Methods In 10 open-chest canines, invasive LV pressure was measured by micromanometer and volume by subendocardial piezoelectric crystals. Echocardiography provided non-invasive 3D LV volumes and valve event timings. The pressure curve was estimated by adjusting a reference curve to the valve events and measured peak LV pressure. Invasive LV end-systolic elastance (Ees) was obtained from multiple PV -loops during preload reduction through least square regression of the points on the PV-loops in the upper left corner with longest normalized distance from loop center. Non-invasive Ees was estimated using a simplified one-beat approach as the slope of a line drawn from this PV-loop point to the origin (Figure 1A). Invasive and non-invasive Ees, along with contractility indices peak LV pressure (Pmax)/end-diastolic volume (EDV) and LV pressure at end-systole (Pes)/EDV, were compared during baseline and during dobutamine infusion. Results As shown in the representative experiment illustrated in Figure 1A, non-invasive Ees captured changes in LV contractility in a similar manner as compared to invasive Ees. Indeed, this was consistent across all experiments, resulting in significant increase in non-invasive Ees in parallel with invasive Ees during dobutamine infusion (p < 0.001 for both) (Figure 1B). Consequently, there was a strong correlation and good agreement between the two methods (r = 0.63, p = 0.003; mean difference – 1.5, SD 2.4) (Figure 1C). For LV contractility indices Pmax/EDV and Pes/EDV, results were comparable: both increased significantly during dobutamine infusion, similar to invasive Ees. This was consistent across all experiments, without exceptions (Figure 2A). Consequently, there were strong correlations between Pmax/EDV and Pes/EDV and invasive Ees (r = 0.77, p = 0.0001 and r = 0.79, p < 0.0001, respectively) (Figure 2B). Conclusions 3D echocardiography provides a reliable and non-invasive method for assessing LV contractility, with good agreement with traditional invasive gold standard Ees. These findings support the use of 3D echocardiography as an accurate and easily accessible alternative for evaluating LV contractility in clinical settings. Invasive vs non-invasive LV Ees Pmax/EDV and Pes/EDV

The myometrial transcriptome changes in mares with endometrosis

Mares with endometrosis exhibit histological changes not only in the endometrium but also in the myometrium that suggest possible functional impairment. The molecular background of these changes is not well understood. We hypothesize that the transcriptomic profile of the mare myometrium varies depending on the degree of endometrosis in mares. Myometria were collected from mares in the mid-luteal phase of the estrous cycle with endometrium categories I, IIA, IIB, and III (∑n = 23), according to Kenney and Doig´s histopathological classification. Myometrial RNA was isolated and subjected to RNA-seq analysis to identify differentially expressed transcriptionally active regions (deTARs) and their contribution to signaling pathways (KEGG database) and biological processes (GO terms). In results, 665, 491 and 499 deTARs were found in the myometrium of mares with endometrium IIA vs I, IIB vs I and III vs I, respectively. 200 common deTARs in the myometrium across all stages of endometrosis (IIA, IIB, and III) vs I were identified. Evaluated deTARs enriched several KEGG pathways including calcium signaling, cAMP signaling, oxytocin signaling, ECM-receptor interaction, and focal adhesion, and were classified into various GO terms including adaptive immune response, tissue homeostasis, muscle contractions, muscle development, and other. In conclusion, transcriptomic alterations in the myometrium of mares with endometrosis may indicate an impaired function of the contractile machinery, mechanisms regulating calcium influx and handling, as well as changes in ECM composition, leading to a decreased contractile activity and structural changes in the myometrium of affected mares.

The effect of lysophosphatidic acid on myometrial contractility and the mRNA transcription of its receptors in the myometrium at different stages of endometrosis in mares

BackgroundEndometrosis (chronic degenerative endometritis) results in morphological changes in the equine endometrium and impairs its secretory function. However, the effect of this condition on the myometrium remains unclear. Lysophosphatidic acid (LPA) may affect female reproductive function and embryo transport by influencing uterine contractility through its receptors (LPARs). The objective of this study was to determine myometrial LPAR1–6 mRNA transcription, and the effects of LPA on myometrial contractions in mares with endometrosis during the mid-luteal and follicular phases of the estrous cycle.ResultsA reduction in myometrial LPAR1 mRNA transcription was observed in mares with endometrosis during the mid-luteal phase, in comparison to those with category I endometria (P < 0.05). While, upregulation of myometrial LPAR3 or LPAR6 mRNA transcription was observed in mares with category III or IIB endometria; respectively (P < 0.05). An increase in myometrial LPAR1, LPAR3 and LPAR5 mRNA transcription was observed during the follicular phase in mares with category IIA endometrium in comparison to their expression in category I endometrium (P < 0.05). During endometrosis progression LPA reduced the force of myometrial contractions in both phases of the estrous cycle (P < 0.05). However, in mares with category IIA endometrium during the follicular phase, LPA was found to increase the force of contraction of myometrial strips in comparison to mares with category I endometrium (P < 0.01).ConclusionIn the course of endometrosis in mares, a disruption in the myometrial mRNA transcription of LPARs has been observed. This is the first study to examine the impact of LPA on myometrial contractility at diffrent stage of endometrosis. However, it is essential to consider that multiple factors may contribute to this process. Alternations in contractile activity and changes in myometrial LPARs mRNA transcription may indicate impaired LPA-signaling mechanisms in equine myometrium during endometrosis.

Two Different Hemodynamic Responses in ME/CFS Patients with Postural Orthostatic Tachycardia Syndrome During Head-Up Tilt Testing.

Introduction: While the diagnosis of postural orthostatic tachycardia syndrome (POTS) is based on heart rate (HR) and blood pressure (BP) criteria, the pathophysiology of POTS is not fully understood as multiple pathophysiological mechanisms have been recognized. Also, cardiac function, being dependent on preload, afterload, contractility, and HR, has not been properly studied. Preload and contractility changes can be inferred from stroke volume index (SVI) changes during a tilt test. Afterload plays a minor role in POTS as a normal BP response is a prerequisite for POTS. Therefore, we analyzed the HR-SVI relation during a tilt test in myalgic encephalomyelitis (ME/CFS) patients with POTS and compared the data with ME/CFS patients with a normal HR-BP response and with that of healthy controls (HC). Material and Methods: In ME/CFS patients with either POTS (n = 233) or a normal HR-BP response (n = 507) and healthy controls (n = 48), we measured SVI (by suprasternal echo), HR, and BP during the tilt. Results: In all ME/CFS patients, the decrease in SVI was larger compared to HC. In patients with a normal HR-BP response and in POTS patients with a HR increase between 30-39 bpm, there was an inverse relationship between the HR increase and SVI decrease during the tilt, compatible with increased venous pooling. In POTS patients with a HR increase ≥40 bpm, this inverse relation was lost, and SVI changes were significantly less compared to POTS patients with a HR increase between 30-39 bpm, suggestive of a hyperadrenergic response. Conclusions: In ME/CFS patients with POTS, two different hemodynamic profiles can be observed: in patients with a limited HR increase, mainly increased venous pooling is observed, while in patients with a large (≥ 40 bpm) HR increase the data are suggestive of a hyperadrenergic response. These two different profiles may have different therapeutic implications.

Bioelectronic block of stellate ganglia mitigates pacing-induced heterogeneous release of catecholamine and neuropeptide Y in the infarcted pig heart.

The sympathetic nervous system modulates cardiac contractile and electrophysiological function and contributes to adverse remodelling following myocardial infarction (MI). Axonal modulation therapy (AMT), directed at the sympathetic chain, blocks efferent sympathetic outflow to the heart and is a strategy to transiently and controllably mitigate chronic MI-associated sympatho-excitation. In porcine models, we evaluated scalable AMT, directed at the paravertebral chain, in blocking reflex-mediated pacing-induced sympatho-excitation post-MI. The level of sympatho-excitation was assessed by dynamic interstitial measurement of noradrenaline (NA) and neuropeptide Y (NPY). In anaesthetized normal (n=5) and age-matched pigs 6weeks post-MI induction (n=10), we electrically stimulated the right sympathetic chain and determined levels of direct current block applied at the T1-T2 level sufficient to reduce the evoked changes in heart rate and/or contractility by 25-75%. Reflex-mediated neural release of NA and NPY into the interstitial space during programmed pacing (PP) was assessed using fast-scanning cyclic voltammetry and capacitive immunoprobes. Normal animals demonstrated homogeneous NA and NPY release profiles during PP. In contrast, for MI animals PP evoked differential NA and NPY release in remote and MI border zones of the left ventricle. Right-sided AMT mitigated NA and NPY pacing-induced release in the remote left ventricle with a positive correlation to increasing AMT levels. Pacing-induced NA and NPY release in the MI border zone was not mitigated by AMT. Differential effects of AMT on NA and NPY may underlie the anti-arrhythmic effects of partial stellate ganglion block in the setting of chronic MI. KEY POINTS: Programmed cardiac pacing evokes homogeneous noradrenaline (NA) and neuropeptide Y (NPY) release in equivalent areas (e.g. medial and lateral aspects) of the normal left ventricle. Programmed cardiac pacing evokes differential NA and NPY release in remote and border zones of the infarcted left ventricle. Axonal modulation therapy (AMT), using a graded direct current block applied to the stellate ganglia, can proportionally modulate cardiac sympathetic reflexes. Unilateral AMT mitigates NA and NPY release in remote left ventricular tissue, with release negativelycorrelated to increasing AMT levels. Heterogeneities in NA and NPY between the border and remote tissues are reduced by progressive AMT.

Mechanisms of atrial-fibrillation-induced ventricular dysfunction and recovery in the human left ventricular myocardium

Abstract Background Atrial fibrillation (AF) frequently occurs alongside heart failure (HF). Clinical studies indicate improved left ventricular (LV) function following rhythm restoration but the underlying myocardial processes remain unclear. Purpose This study investigated effects of AF and its termination on human LV myocardium as well as potential molecular mechanisms involved in the AF-induced LV dysfunction. Methods Human LV tissue slices obtained from HF patients were long-term cultivated in-vitro. AF was simulated by tachy-arrhythmic culture pacing at 100 bpm with 30% irregularity for 7 days and contractile LV function was compared to slices undergoing sinus rhythm (SR)-simulation (60 bpm/0%). After 7 days, rhythm restoration was simulated by switching to SR-simulation. To elucidate cellular mechanisms involved in AF-induced LV dysfunction, human induced pluripotent stem cell-derived cardiomyocytes (iPSC-CM) were subjected to AF-simulation and examined via epifluorescence microscopy (FURA-2) and confocal microscopy (Fluo-4). Additionally, to investigate the impact of reactive oxygen species (ROS) on cardiomyocytes, iPSC-CM were subjected to treatment with the ROS-scavenger N-acetylcysteine (NAC). Results AF-simulation caused a progressive decline in systolic force of human LV myocardium (n=14 slices) with significantly reduced twitch amplitudes compared to SR-simulation (n=11). Within just 5 days of AF-termination, a significant recovery in LV function was observed, indicated by improved systolic contraction amplitudes. IPSC-CM measurements revealed a significant reduction in systolic Ca2+-transient amplitudes as well as an increased diastolic Ca2+ leak after AF-simulation (n=41) compared to SR-simulation (n=44). However, 5 days after SR-restoration, iPSC-CM exhibited no significant differences anymore, indicating a fast recovery of systolic Ca2+-cycling. We further investigated the impact of ROS on LV function and could show that Ca2+-transient amplitude was preserved after AF-simulation in iPSC-CM when treated with NAC (n=35), suggesting an interplay of ROS with the Ca2+-homeostasis of cardiomyocytes. Conclusions This study demonstrates that AF impairs LV function in human HF myocardium. However, the involved changes in contractility and cardiomyocyte Ca2+ handling are reversible upon AF termination leading to improved LV function already within few days after AF cessation. Moreover, we provided an indication for an interplay of ROS with the Ca2+ homeostasis, endorsing an AF-induced LV-dysfunction, which merits further investigation.

Effect of fatigue on intermuscular EMG-EMG coupling during bench press exercise at 60% 1RM workload in males.

To explore the neuromuscular control mechanism and quantifying the fatigue response during bench press exercise is important references to prescribe an appropriate exercise program. However, current literature struggles to provide a concrete conclusion on the changes of intermuscular EMG-EMG coupling between synergistic and antagonist muscles during the exercise. Thus, the current study was designed to reveal fatigue-related changes of intermuscular EMG-EMG coupling during bench press exercise. Thirty-one healthy male participants performed a bench press exercise on the Smith machine at 60% One Repetition Maximum (1RM) workload to exhaustion, while surface electromyographic signals (sEMG) were collected from triceps brachii (TB), biceps brachii (BB), anterior deltoid (AD), posterior deltoid (PD), and pectoralis major (PM). Surface EMG signals were divided into the first half and second half of the bench press exercise. Phase synchronization index (PSI) was calculated between sEMG of synergistic muscle pairs AD-TB, AD-PM and antagonist muscle pairs BB-TB, AD-PD. EMG power of TB, AD, PD, PM muscles in alpha (8-12 Hz) frequency band and EMG power of each muscle in beta (15-35 Hz), and gamma (35-60 Hz) frequency bands were all increased during the second half of contraction compared with the first half of contraction. PSI of gamma frequency band was significantly decreased in BB-TB muscle pair while EMG-EMG coupling of AD-TB in gamma frequency band was significantly increased during the second half of contraction compared to the first half of contraction. The results indicated a decrease of interconnection between synchronized cortical neurons and the motoneuron pool of BB and TB, and an increase of interconnection between AD-TB muscles during fatiguing bench press exercise at 60% 1RM workload. The changes of intermuscular coupling may be related to the supraspinal modulations to compensate for the decrease of muscle force as well as a result of unbalanced changes of agonist and antagonist muscle contractility.

Time-dependent arachidonic acid metabolism and functional changes in rats bladder tissue after suprasacral spinal cord injury

BackgroundA critical aspect affecting the quality of life in Traumatic spinal cord injury (TSCI) patients is bladder dysfunction. Metabolities in arachidonic acid are crucial lipid signaling molecules involved innumerous physiological processes. In this study, We are the first use eicosanoid metabolomics detrusor contraction examine, to assess the effect of the arachidonic acid metabolic in bladder dysfunction following TSCI. In additon, we explore the time of inflammatory and function changes in bladder tissue. MethodsAdult male Sprague-Dawley rats were subjected to improved Weight Drop method surgeries. Detrusor contraction examination, urodynamic examination, eicosanoid metabolomics, transmission electron microscopy, Elisa and histological staining were performed to assess the change of inflammatory, metabolic and function variation over time after TSCI. ResultsFollowing TSCI, before the variations of bladder function, inflammatory changes including the increase of inflammatory factors, mitochondrial damage, and slight lipid peroxidation, occurred in bladder tissue. And the inflammatory changes gradually decreases over time. However, From the third day after TSCI, secondary lesions appeared in bladder tissue. Not only did inflammation-related indexes increase again, the degree of mitochondrial damage and lipid peroxidation increased, but also the contractility of detrusor began to change significantly. We also found that the content of metabolites in arachidonic acid metabolic pathway and the degree of detrusor contractility change showed a strong correlation. In addition, we found that rats had moved beyond the spinal shock stage on the seventh day after TSCI. ConclusionAltogether, we are the first to demonstrate that abnormal arachidonic acid metabolism plays an important role in bladder dysfunction after TSCI. We also demonstrate that 3d is a critical juncture for changes in rat bladder tissue, which indicates it is an important juncture in the treatment of neurogenic bladder.

37 - The change of detrusor contractility at 5 years after transurethral resection of the prostate: a single center prospective observational study

37 - The change of detrusor contractility at 5 years after transurethral resection of the prostate: a single center prospective observational study

Association of the echocardiographic parameters with the physical dimension of quality of life

Heart failure (HF) is determined by pathophysiologic changes in the left ventricle (LV) that occur before the onset of clinical symptoms; these changes can lead to mitral insufficiency that will maintain and favor ventricular dysfunction. An associated change in contractility occurs which will maintain the vicious circle. 252 patients with HF were included in this cross-sectional analysis. Patients were divided into two groups, Group I-S/V (n = 55) and Group II-CT (n = 197) to comparatively assess cardi-ac parameters according to the administered therapy and to determine their correlation with quality of life domains. 2D measurements were performed to determine ultrasound parameters. The WHOQOL-BREF questionnaire was used to assess the quality of life. When analyzing the mean values of the determined echocardiographic parame-ters, significant differences in LV ejection fraction (LVEF) (p &lt; 0.03) Results: Analysing the mean values of the echocardiographic parameters determined, significant differences in LV ejection fraction (LV ejection fraction (LVEF) (p &lt; 0.001) and right ventricular diameter (p = 0.030) were found between the two study groups. The incidence of aortic regurgitation and tricuspid regurgitation was higher in the I-S/V group (40% vs. 25%, p = 0.001, respec-tively 47% vs. 35%, p = 0.03). Mitral regurgitation was present in relatively similar per-centages. Testing the association of echocardiographic parameters with quality of life do-mains showed a significant association of LVEF with physical health and relationship with the environment (p = 0.002, r = 0.143, respectively p = 0.041, r = 0.129). Physical dimension and relationship with the environment are more affected in pa-tients with low LVEF. Routine echocardiographic evaluation is essential in the global as-sessment of the HF patient and may suggest a low quality of life with impaired physical dimension.

Airborne polystyrene nanoplastics exposure leads to heart failure via ECM-receptor interaction and PI3K/AKT/BCL-2 pathways

Environmental contamination has been recognized as a significant threat to human well-being, and recent findings of microplastic presence in human cardiac tissues have raised concerns. However, research on the effects of airborne nanoplastics (NPs) on cardiac physiology remains limited. We utilized a comprehensive body exposure apparatus to simulate the impact of airborne polystyrene NPs pollution, focusing on understanding how airborne NPs affect cardiac morphology and function. Following two weeks of NPs exposure, mice exhibited a 23.89 ± 8.30 % reduction in heart mass, a 20.05 ± 2.97 % decrease in heart rate as detected, and a myocardial electrical conduction block. Echocardiography showed significant changes in cardiac contractility, with increases in cardiac ejection fraction and stroke volume of 13.00 ± 3.00 % and 43.00 ± 17.00 %, respectively. In addition, histologic assessments revealed signs of ventricular hypertrophy, ventricular myocardial hypertrophy, and myocardial necrotic fibrosis. Of particular interest, our mechanistic investigations highlighted the harmful effects of NPs on cardiac structure and function, mediated through extracellular matrix (ECM) receptor interactions and the PI3K/AKT/BCL-2 signaling pathway. The insights gained provide a foundation for understanding the risks posed by airborne NPs to human cardiac health, emphasizing the need for increased vigilance and implementation of mitigation strategies in environmental management.

Dedifferentiation- and aging-induced loss of mechanical contractility and polarity in vascular smooth muscle cells: Heterogeneous changes in macroscopic and microscopic behavior of cells in serial passage culture

Dedifferentiation and aging of vascular smooth muscle cells (VSMCs) are associated with serious vascular diseases, such as arteriosclerosis and aneurysm. However, how cell dedifferentiation and aging affect cellular mechanical behaviors at the single-cell and intracellular structure levels remains unclear. An in-depth understanding of these interactions is extremely important for understanding the mechanism underlying VSMC mechanical integrity and homeostatic regulation of vascular walls. Herein, we systematically investigated changes in VSMC morphology, structure, contractility, and motility during dedifferentiation and aging induced by serial passage culture using traction force microscopy with elastic micropillar substrates, laser nanodissection of cytoskeletons, confocal fluorescence microscopy, and atomic force microscopy. We found that VSMC dedifferentiation started in the middle stage of serial passage culture, accompanied by a transient cell spreading in the cell width and decrease in contractile protein expression. Dedifferentiated VSMCs showed a significant decrease in the contraction and stiffness of individual actin stress fibers; however, their overall cell traction forces were maintained. Simultaneously, a significant increase in cell motility and the number of actin fibers was observed in dedifferentiated VSMCs, which may be associated with the enhancement of cell migration and disruption of cell/tissue integrity during the early stage of vascular diseases. As cell senescence progressed in the later stage of serial passage culture, VSMCs displayed reduced cell spreading and migration with decrease in the overall cell traction forces and drastic reduction in mechanical polarity of cell structures and forces. These results suggested that cell senescence causes loss of mechanical contractility and polarity in VSMCs, which may be an important factor in vascular disease progression. The experimental systems established in this study can be powerful tools for understanding the mechanisms underlying cellular dedifferentiation and aging from a biomechanical perspective.

Real-Time Wireless Sensing of Cardiomyocyte Contractility by Integrating Magnetic Microbeam and Oriented Nanofibers.

In vitro cardiomyocyte mechano-sensing platform is crucial for evaluating the mechanical performance of cardiac tissues and will be an indispensable tool for application in drug discovery and disease mechanism study. Magnetic sensing offers significant advantages in real-time, in situ wireless monitoring and resistance to ion interference. However, due to the mismatch between the stiffness of traditional rigid magnetic material and myocardial tissue, sensitivity is insufficient and it is difficult to achieve cell structure induction and three-dimensional cultivation. Herein, a magnetic sensing platform that integrates a neodymium-iron-boron/polydimethylsiloxane (NdFeB/PDMS) flexible microbeam with suspended and ordered polycaprolactone (PCL) nanofiber membranes was developed, providing a three-dimensional anisotropic culture environment for cardiomyocyte growth and simultaneously realizing in situ wireless contractility monitoring. The as-prepared sensor presented an ultrahigh sensitivity of 442.2 μV/μm and a deflection resolution of 2 μm. By continuously monitoring the cardiomyocyte growth status and drug stimulation feedback, we verified the capability of the platform to capture dynamic changes in cardiomyocyte contractility. This platform provides a perspective tool for evaluating cardiomyocyte maturity and drug performance.

Abstract Mo117: Investigation of Mechanisms to Modulate Contractility in 13-Lined Ground Squirrels

Introduction: During hibernation, 13-lined ground squirrels cycle between torpor and intermittent bouts of arousal (IBA). Bouts of IBA last 12-48 hours, during which heart rates rise from 2-4 bpm in torpor to 300 bpm during IBA before returning to torpor. Thus, rates of contractility and relaxation and their mechanisms must rapidly change. Phosphorylation of cardiac troponin I (cTnI) at serine 23/24 (pSer23/24) has been shown to decrease calcium sensitivity and increase the rate of myocardial relaxation, enabling faster heart rates. Heat shock protein 27 (HSP27) has been shown to protect contractility by stabilizing troponin. Hypothesis: We hypothesized that cTnI Ser23/24 phosphorylation would be higher in summer and IBA and that HSP27 would be found in higher quantities during torpor and IBA. Methods and Results: Left ventricular tissue (summer, n=8; torpor, n=8; IBA, n=8) was solubilized, separated by SDS-PAGE, and blotted with antibodies for quantification. The pSer23/24 to total troponin ratios were higher in summer compared to torpor (1.22±0.75 vs 0.32±0.19, p=0.003) and IBA (0.57±0.19, p=0.03), but not different between IBA and torpor. No significant season-dependence was observed for the serine 43 cTnI phosphorylation to total troponin ratio (torpor 1.45±0.69, summer 1.05±0.34, IBA 1.15±0.84). No significant season-dependence was observed in HSP27 (normalized to GAPDH) (summer 0.09±0.02, IBA 0.14±0.10, torpor 0.16±0.08). Nor was there a significant season-dependence observed in HSP90 (normalized to GAPDH) (summer 1.57±0.66, IBA 1.13±0.19, torpor 1.22±0.21). Conclusions: None of these mechanisms fully explain the rapid change in contractility observed during the hibernating periods of 13-lined ground squirrels. Other post-translational modifications of troponin or modifiers of HSP activity may modify the reported results. Such regulation may identify new treatments for humans where rapid changes in heart rate or contractility occur.

Load Dependency of Ventricular Pump Function: Impact on the Non-Invasive Evaluation of the Severity and the Prognostic Relevance of Myocardial Dysfunction.

Ventricular pump function, which is determined by myocyte contractility, preload and afterload, and, additionally, also significantly influenced by heart rhythm, synchrony of intraventricular contraction and ventricular interdependence, explains the difficulties in establishing the contribution of myocardial contractile dysfunction to the development and progression of heart failure. Estimating myocardial contractility is one of the most difficult challenges because the most commonly used clinical measurements of cardiac performance cannot differentiate contractility changes from alterations in ventricular loading conditions. Under both physiological and pathological conditions, there is also a permanent complex interaction between myocardial contractility, ventricular anatomy and hemodynamic loading conditions. All this explains why no single parameter can alone reveal the real picture of ventricular dysfunction. Over time there has been increasing recognition that a load-independent contractility parameter cannot truly exist, because loading itself changes the myofilament force-generating capacity. Because the use of a single parameter is inadequate, it is necessary to perform multiparametric evaluations and also apply integrative approaches using parameter combinations which include details about ventricular loading conditions. This is particularly important for evaluating the highly afterload-sensitive right ventricular function. In this regard, the existence of certain reluctance particularly to the implementation of non-invasively obtainable parameter combinations in the routine clinical praxis should be reconsidered in the future. Among the non-invasive approaches used to evaluate ventricular function in connection with its current loading conditions, assessment of the relationship between ventricular contraction (e.g., myocardial displacement or deformation) and pressure overload, or the relationship between ejection volume (or ejection velocity) and pressure overload, as well as the relationship between ventricular dilation and pressure overload, were found useful for therapeutic decision-making. In the future, it will be unavoidable to take the load dependency of ventricular function much more into consideration. A solid basis for achieving this goal will be obtainable by intensifying the clinical research necessary to provide more evidence for the practical importance of this largely unsolved problem.

Mechanisms of a novel regulatory light chain-dependent cardiac myosin inhibitor.

Hypertrophic cardiomyopathy (HCM) is a genetic disease of the heart characterized by thickening of the left ventricle (LV), hypercontractility, and impaired relaxation. HCM is caused primarily by heritable mutations in sarcomeric proteins, such as β myosin heavy chain. Until recently, medications in clinical use for HCM did not directly target the underlying contractile changes in the sarcomere. Here, we investigate a novel small molecule, RLC-1, identified in a bovine cardiac myofibril high-throughput screen. RLC-1 is highly dependent on the presence of a regulatory light chain to bind to cardiac myosin and modulate its ATPase activity. In demembranated rat LV trabeculae, RLC-1 decreased maximal Ca2+-activated force and Ca2+ sensitivity of force, while it increased the submaximal rate constant for tension redevelopment. In myofibrils isolated from rat LV, both maximal and submaximal Ca2+-activated force are reduced by nearly 50%. Additionally, the fast and slow phases of relaxation were approximately twice as fast as DMSO controls, and the duration of the slow phase was shorter. Structurally, x-ray diffraction studies showed that RLC-1 moved myosin heads away from the thick filament backbone and decreased the order of myosin heads, which is different from other myosin inhibitors. In intact trabeculae and isolated cardiomyocytes, RLC-1 treatment resulted in decreased peak twitch magnitude and faster activation and relaxation kinetics. In conclusion, RLC-1 accelerated kinetics and decreased force production in the demembranated tissue, intact tissue, and intact whole cells, resulting in a smaller cardiac twitch, which could improve the underlying contractile changes associated with HCM.

FORENSIC-MEDICAL FEATURES OF THE HEART IN CASES OF ACUTE CORONARY INSUFFICIENCY WITH SUDDEN CARDIAC DEATH

The article provides an assessment of changes in the endocardium of the atria and ventricles of the heart in cases of sudden cardiac death due to acute coronary insufficiency. In cases of sudden death due to acute coronary insufficiency, distinct focal pathological changes were observed in the connective tissue of the endocardium of the left atrium and ventricle, manifested by loss of fibrillar structures and fragmentation of its non-cellular elements. This corresponded to local contractile changes in the cardiomyocytes, localised in the subendocardial space of the affected parts of the heart, leading to local fragmentation and an increase in the thickness of the endocardial folds. In addition, the loss of their characteristic waviness and the acquisition of linearity were observed. These changes are considered to be manifestations of morpho-functional disorders of the endocardium of the specified heart segments. The aim of the study was to determine the characteristics of endocardial changes in the atria and ventricles in cases of sudden death due to acute ischaemic heart disease. Materials and Methods. The study material included 12 hearts from young and middle-aged individuals without cardiovascular disease (control group) and 12 hearts from working-age individuals who died suddenly of acute ischaemic heart disease. Conclusions: At the time of death from acute ischaemic heart disease, there were pronounced focal pathological changes in cellular and non-cellular components in the connective tissue of the endocardium of the left atrium and ventricle. These changes caused focal contractile changes in cardiomyocytes localised in the subendocardial layer of the myocardium of the left ventricle. The identified changes in the subendocardial layer of the myocardium caused focal thickening, fragmentation, and increased thickness of the endocardial folds, their undulation, which can be considered as manifestations of morpho-functional disorders of the endocardium.

Detection of contractility changes in the heart from arterial blood pressure data using symmetric Projection Attractor Reconstruction

The potential for unintended drug induced changes in cardiac contractility is a major concern in medicines development. Whilst direct left ventricular pressure (LVP) measurement is the gold standard for measuring cardiac contractility in vivo, it is resource intensive and poses a welfare burden on research animals. In contrast, arterial blood pressure (BP) measurement has fewer challenges. Symmetric Projection Attractor Reconstruction (SPAR) is a signal processing technique which transforms physiological time-series signals into a corresponding visual image (‘attractor’), amplifying morphology changes within physiological waveforms. It was hypothesized that SPAR analysis of BP signals would provide a surrogate measure of cardiac contractility by specifically amplifying the maximum slope of the systolic upstroke. BP (abdominal aorta) signals obtained from beagle dogs, treated with positive and negative inotropes, were retrospectively analysed to identify signal features that correlated with the maximum upslope of the LVP signal from simultaneously acquired LVP recordings. SPAR transformation of BP signals quantified drug induced changes in the maximum slope of the systolic upstroke. We identified key SPAR metrics that provided >0.8 correlation with the LVP maximum upslope, outperforming the BP systolic upstroke alone. This was observed for all 4 different drugs, doses and time points evaluated across studies. Thus, we conclude that the SPAR measures derived from the BP signal could be used as a first pass in vivo screen to flag any risk of drug induced changes in cardiac contractility during the conduct of non-clinical medicines development, potentially reducing or replacing the need to perform direct left ventricular measurements.