The morphology of the elements of the myocardial contractile apparatus question and research prospects

Background. Over the past 50 years, specific methods for studying the ultrastructure of the heart have been rapidly developed. The complex interaction of various research methods makes it possible to more accurately form a representation of the spatial structure of the components of the myocardial contractile apparatus. Objective. To conduct a content analysis of the results of the study of the composition of the myocardial contractile apparatus. Conduct a broad analysis of literary references and form an understanding of the spatial structure of the components of the myocardial contractile apparatus in the prospect of research at different levels of cell organization. Methods. Processing of information sources was carried out by the method of complex meta-analysis of data analysis. Results. The morphological characteristics of the myocardial contractile apparatus include a number of broad profile elements. The system of composite elements of the contractile apparatus of cardiomyocytes is the most formed and developed in the structure of the cytoplasmic complex of organelles in the group of contractile cardiomyocytes. The complex of the contractile apparatus is represented by myofibrils, each of which consists of thousands of sarcomeres telophragm connected in series, containing actin (thin) and myosin (thick) myofilaments. The main methods for studying the contractile apparatus of the myocardium include how immunohistochemistry and transmission electron microscopy provide an understanding of the structure of components at various levels of organization of histoarchitectonics and ultrastructure of organelles.. The contractile apparatus of the myocardium includes species-specific organelles, which basically belong to a number of basic hardware systems of cardiomyocytes. Conclusion. Immunohistochemical methods should clearly show the localization of individual tipes of elements in the protein structure of the contractile apparatus of the myocardium, and therefore should include in the study methods the use of the following immunohistochemical markers that can show the configuration of thin and thick myofilaments. The results of analytical review and analysis of information sources on the characteristics of the components of the myofibrillar complex gives a choice of specific research methods and forms a more detailed understanding of the spatial organization of the morphology of the myocardial contractile apparatus.

Clot Retraction: Cellular Mechanisms and Inhibitors, Measuring Methods, and Clinical Implications

Platelets have important functions in hemostasis. Best investigated is the aggregation of platelets for primary hemostasis and their role as the surface for coagulation leading to fibrin- and clot-formation. Importantly, the function of platelets does not end with clot formation. Instead, platelets are responsible for clot retraction through the concerted action of the activated αIIbβ3 receptors on the surface of filopodia and the platelet’s contractile apparatus binding and pulling at the fibrin strands. Meanwhile, the signal transduction events leading to clot retraction have been investigated thoroughly, and several targets to inhibit clot retraction have been demonstrated. Clot retraction is a physiologically important mechanism allowing: (1) the close contact of platelets in primary hemostasis, easing platelet aggregation and intercellular communication, (2) the reduction of wound size, (3) the compaction of red blood cells to a polyhedrocyte infection-barrier, and (4) reperfusion in case of thrombosis. Several methods have been developed to measure clot retraction that have been based on either the measurement of clot volume or platelet forces. Concerning the importance of clot retraction in inborn diseases, the failure of clot retraction in Glanzmann thrombasthenia is characterized by a bleeding phenotype. Concerning acquired diseases, altered clot retraction has been demonstrated in patients with coronary heart disease, stroke, bronchial asthma, uremia, lupus erythematodes, and other diseases. However, more studies on the diagnostic and prognostic value of clot retraction with methods that have to be standardized are necessary.

Biomechanical Properties of the Sarcolemma and Costameres of Skeletal Muscle Lacking Desmin

Intermediate filaments (IFs), composed primarily by desmin and keratins, link the myofibrils to each other, to intracellular organelles, and to the sarcolemma. There they may play an important role in transfer of contractile force from the Z-disks and M-lines of neighboring myofibrils to costameres at the membrane, across the membrane to the extracellular matrix, and ultimately to the tendon (“lateral force transmission”). We measured the elasticity of the sarcolemma and the connections it makes at costameres with the underlying contractile apparatus of individual fast twitch muscle fibers of desmin-null mice. By positioning a suction pipet to the surface of the sarcolemma and applying increasing pressure, we determined the pressure at which the sarcolemma separated from nearby sarcomeres, Pseparation, and the pressure at which the isolated sarcolemma burst, Pbursting. We also examined the time required for the intact sarcolemma-costamere-sarcomere complex to reach equilibrium at lower pressures. All measurements showed the desmin-null fibers to have slower equilibrium times and lower Pseparation and Pbursting than controls, suggesting that the sarcolemma and its costameric links to nearby contractile structures were weaker in the absence of desmin. Comparisons to earlier values determined for muscles lacking dystrophin or synemin suggest that the desmin-null phenotype is more stable than the former and less stable than the latter. Our results are consistent with the moderate myopathy seen in desmin-null muscles and support the idea that desmin contributes significantly to sarcolemmal stability and lateral force transmission.

Asthmatic Eosinophils Promote Contractility and Migration of Airway Smooth Muscle Cells and Pulmonary Fibroblasts In Vitro

Enhanced contractility and migration of airway smooth muscle cells (ASMC) and pulmonary fibroblasts (PF) are part of airway remodeling in asthma. Eosinophils are the central inflammatory cells that participate in airway inflammation. However, the role of asthmatic eosinophils in ASMC and PF contractility, migration, and differentiation to contractile phenotype has not yet been precisely described. A total of 38 individuals were included in this study: 13 steroid-free non-severe allergic asthma (AA) patients, 11 severe non-allergic eosinophilic asthma (SNEA) patients, and 14 healthy subjects (HS). For AA patients and HS groups, a bronchial allergen challenge with D. pteronyssinus was performed. Individual combined cell cultures were prepared from isolated peripheral blood eosinophils and immortalized ASMC or commercial PF cell lines separately. The migration of ASMC and PF was evaluated using wound healing assay and contractility using collagen gel assay. Gene expression of contractile apparatus proteins, COL1A1, COL5A1, and FN, in ASMC and PF was evaluated using qRT-PCR. We found that contractility and migration of ASMC and PF significantly increased after incubation with asthmatic eosinophils compared to HS eosinophils, p < 0.05, and SNEA eosinophils demonstrated the highest effect on contractility of ASMC and migration of both cell lines, p < 0.05. AA and SNEA eosinophils significantly increased gene expression of contractile apparatus proteins, COL1A1 and FN, in both cell lines, p < 0.05. Furthermore, the allergen-activated AA eosinophils significantly increased the contractility of ASMC, and migration and gene expression in ASMC and PF, p < 0.05. Thus, asthmatic eosinophils change ASMC and PF behavior by increasing their contractility and migration, contributing to airway remodeling.

Investigation of the temporal and spatial dynamics of muscular action potentials through optically pumped magnetometers

ABSTRACTAimThis study aims to simultaneously record the magnetic and electric components of the propagating muscular action potential.MethodA single-subject study of the monosynaptic stretch reflex of the musculus rectus femoris was performed; the magnetic field generated by the muscular activity was recorded in all three spatial directions by five optically pumped magnetometers. In addition, the electric field was recorded by four invasive fine-wire needle electrodes. The magnetic and electric fields were compared, and modelling and simulations were performed to compare the magnetic field vectors with the underlying muscular anatomy of the rectus femoris muscle.ResultsThe magnetomyography (MMG) signal can reliably be recorded following the stimulation of the monosynaptic stretch reflex. The MMG signal shows several phases of activity inside the muscle, the first of which is the propagating muscular action potential. As predicted by the finite wire model, the magnetic field vectors of the propagating muscular action potential are generated by the current flowing longitudinal to the muscle fiber. Based on the magnetic field vectors, it was possible to reconstruct the pinnation angle in the muscle. The later magnetic components are linked to the activated contractile apparatus.InterpretationMMG allows to analyze the muscle physiology from the propagating muscular action potential to the initiation of the contractile apparatus. At the same time this methods reveal information about muscle fiber direction and extend. With the development of high-resolution magnetic cameras, it will be possible to image the function and structure of any skeletal muscle with high precision. This method could be used in clinical medicine but also in sports and training science.What this paper adds-A robust technique for triggering a muscular action potential that can be recorded by MMG and needle EMG simultaneously-The correlation of the MMG signal with the needle EMG signal-A method for detecting the direction of the propagating muscular action potential-A method for correlating the magnetic field vectors with the pinnation angle of the examined muscle

Hypoxic modulation of fetal vascular MLCK abundance, localization, and function

Changes in vascular contractility are among the most important physiological effects of acute and chronic fetal hypoxia. Given the essential role of myosin light-chain kinase (MLCK) in smooth muscle contractility and its heterogeneous distribution, this study explores the hypothesis that subcellular changes in MLCK distribution contribute to hypoxic modulation of fetal carotid artery contractility. Relative to common carotid arteries from normoxic term fetal lambs (FN), carotids from fetal lambs gestated at high altitude (3,802 m) (FH) exhibited depressed contractility without changes in MLCK mRNA or protein abundance. Patterns of confocal colocalization of MLCK with α-actin and 20-kDa regulatory myosin light chain (MLC20) enabled calculation of subcellular MLCK fractions: 1) colocalized with the contractile apparatus, 2) colocalized with α-actin distant from the contractile apparatus, and 3) not colocalized with α-actin. Chronic hypoxia did not affect MLCK abundance in the contractile fraction, despite a concurrent decrease in contractility. Organ culture for 72 h under 1% O2 decreased total MLCK abundance in FN and FH carotid arteries, but decreased the contractile MLCK abundance only in FH carotid arteries. Correspondingly, culture under 1% O2 depressed contractility more in FH than FN carotid arteries. In addition, hypoxia appeared to attenuate ubiquitin-independent proteasomal degradation of MLCK, as reported for other proteins. In aggregate, these results demonstrate that the combination of chronic hypoxia followed by hypoxic culture can induce MLCK translocation among at least three subcellular fractions with possible influences on contractility, indicating that changes in MLCK distribution are a significant component of fetal vascular responses to hypoxia.

Conceptualizing conduction as a pliant vasomotor response: impact of Ca2+ fluxes and Ca2+ sensitization

Conducted vasomotor responses depend on electrical spread in the vascular wall and its translation into vasomotor responses. Our computational investigation highlights how the regulatory state of the contractile apparatus can shape conduction without interfering with the underlying electrical spread. Contractile machinery is regulated, e.g., by regional endocrine or mechanical signals. We further illustrate how regional contractile regulation can work cooperatively with electrical spread to optimize perfusion to local tissue demands.

Abstract 304: Adaptive Sarcomeric Remodeling of Left Atrial Cardiomyocytes in Non-failing Non-valvular Atrial Fibrillation

Contractile remodeling in sustained atrial fibrillation (AF) has been analyzed by limited studies whose results were confounded by either coexisting systolic heart failure or valve disease (valvular AF) or origin of tissue (right chamber instead of left, atrial appendage instead of main wall). We sought to assess the structural changes in contractile apparatus and its physiological implications on single cardiomyocyte mechanics in patients with non-failing non-valvular AF. We utilized left atrial wall tissue from rejected donor hearts from 5 subjects in sinus rhythm (SR) and 3 with AF (age 50, 2♀ vs 60, 1♀), all with no signs of cardiovascular or valvular disease. Isolated single skinned myocytes were mounted to a force transducer and length controller and set to an initial sarcomere length of 2.1 μm. Isometric active and passive forces were recorded using custom software during [Ca2+] solution switching (0.79 - 46.8 μM). Surprisingly, we found that isometric maximal calcium-activated force (Fmax) was almost two times higher in AF compared to SR patients (n: SR = 15 cells, AF = 9 cells, p < 0.0001). This was unexpected, as previous studies found that AF patients had depressed contractile function, although these were confounded by heart failure and valve disease. There were no differences in calcium sensitivity, hill coefficient, or cell cross-sectional area (CSA) between SR and AF. We next performed 1D SDS-PAGE electrophoresis to compare myosin heavy chain (MHC) isoforms. In SR patients, atrial expression of β-MHC was very low (14% of total MHC expression), but this was significantly elevated in AF patients (37%, p = 0.05). The observed rise in contractile force might be a compensatory adaptation to sustain ventricular filling in initial stages of non-valvular non-failing AF patients. Or it may be a maladaptive response to atrial unloading resulting in wasted energy utilization. The contribution of this cellular increase in contractility to whole organ function is unclear. There is strong evidence that fibrotic remodeling and inflammation play an important role in AF, but the clinical challenge is still significant. Conversely, there has been very little work done on the contractile apparatus in AF, and whether it may represent a possible therapeutic target.

Transcriptomic Profile of Primary Culture of Skeletal Muscle Cells Isolated from Semitendinosus Muscle of Beef and Dairy Bulls

The aim of the study was to identify differences in the transcriptomic profiles of primary muscle cell cultures derived from the semitendinosus muscle of bulls of beef breeds (Limousin (LIM) and Hereford (HER)) and a dairy breed (Holstein-Friesian (HF)) (n = 4 for each breed). Finding a common expression pattern for proliferating cells may point to such an early orientation of the cattle beef phenotype at the transcriptome level of unfused myogenic cells. To check this hypothesis, microarray analyses were performed. The analysis revealed 825 upregulated and 1300 downregulated transcripts similar in both beef breeds (LIM and HER) and significantly different when compared with the dairy breed (HF) used as a reference. Ontological analyses showed that the largest group of genes were involved in muscle organ development. Muscle cells of beef breeds showed higher expression of genes involved in myogenesis (including erbb-3, myf5, myog, des, igf-1, tgfb2) and those encoding proteins comprising the contractile apparatus (acta1, actc1, myh3, myh11, myl1, myl2, myl4, tpm1, tnnt2, tnnc1). The obtained results confirmed our hypothesis that the expression profile of several groups of genes is common in beef breeds at the level of proliferating satellite cells but differs from that observed in typical dairy breeds.