Tension Relaxation Research Articles

Noetic and Noematic Dimensions of Religious Experience

AbstractPhenomenologies of religious experience have been developed by Max Scheler and via Alfred Schutz’s frameworks of “multiple realities” and “finite provinces of meaning.” For both, religious experience resists the pragmatic imperatives of the mechanistic worldview or world of working. Schutz’s paradigm begins with a distinctive noetic religious epoché opening the religious province, in contrast with Scheler’s start with spheres of being (especially the absolute sphere) furnishing the noematic context for religious acts. Scheler’s religious act resembles the religious epoché, but his eidetic analysis highlights the act’s distinctiveness, irreducibility to non-religious acts, and immunity to psychological reductionism. Correlating the religious act with his value theory (the absolute sphere), Scheler better withstands the subordination of religion to the pragmatic imperatives and the absolute to lesser values than does a Schutzian ranking of purposes in the province’s form of spontaneity. Scheler’s absolute personal being, whose revelation one must respectfully wait, supports the Schutzian relaxed tension of consciousness. Respectfulness of persons, the social/communal/critical dimensions of religious experience, religion’s need for critique from theoretical provinces of meaning, and the wariness of idolatrously substituting one’s own finite goods for the absolute can all mitigate the religious imperialism and violence to which absolute commitments can lead.

Amelioration of muscular spasm-induced pain of Guangtongxiao recipe in a non-everted gut sac in vitro model

BackgroundThe modern study of the traditional Chinese medicine (TCM) compound recipes is a complex issue because of the large number of components in the recipes that would produce several metabolites after entering the body. The TCM compound recipes are known to have the advantage of synergistic treatment by multiple targets due to diverse components. Therefore, a research method that can reflect the overall effect of compounds with multi-components is essential. The pharmacological studies of the classic TCM compound recipes mainly use the sero-pharmacological method. It is a semi-in vivo study method, and the drug to be tested in the in vitro experiment is the drug-containing serum from the model animals (the drug to be tested is a mixed drug system containing the prototype drugs in animal bodies that have pharmacodynamic effects and the metabolites). Herein, a safe and effective external TCM recipe was used to develop another semi-in vivo experimental method to reflect the overall effects of TCM. AimTo observe the effects of in-vitro intestinal absorption liquid of aqueous extracts of the TCM compound recipe—Guangtongxiao foam aerosol (Guangtongxiao)—on the tension of isolated rectal rings of mouse and investigate the underlying mechanisms of antispasmodic and amelioration of muscular spasm-induced pain. MethodsIntestinal absorption liquid of the Guangtongxiao aqueous extract at the five time points (30, 45, 75, 105, and 120 min) was prepared using a non-everted gut sac method. The isolated rectal rings of mice were prepared by pre-contraction using potassium chloride (KCl) or acetylcholine chloride (ACh) to make steady contraction. The intestinal absorption liquid were added cumulatively to the sink with the constricted rectal rings. The effects of the five groups of the intestinal absorption liquid with different drug concentration were observed on the tension of the isolated rectal rings. Then the ex vivo perfusion of the mouse rectal ring was performed as same as Guangtongxiao intestinal absorption liquid experiments, and the effects of two major components of Guangtongxiao, paeoniflorin (Pae) and tetrahydropalmatine (THP), on the rectal ring pre-treated with high concentration of KCl and ACh to induce contraction were studied. ResultsThe relaxation rate of the five groups of the intestinal canals increased significantly with 3200 μL cumulative sample volume as compared to the blank group (P < 0.01). It suggested that the relaxation activity of the intestinal absorption liquid enhanced significantly with the prolongation of the interaction between isolated rectal rings and intestinal absorption liquid in a time-dependent manner. Also, significant differences were detected while comparing between the 120-min intestinal absorption liquid group and the blank group with respect to various cumulative sampling volumes (P < 0.01). In addition, the intestinal relaxation rate elevated gradually with the increase in sampling volume, indicating that the concentrations of active substances in the intestinal absorption liquid prepared by the non-everted gut sac model increased and the intestinal relaxation activity was enhanced with the prolongation of the absorption time in a dose-dependent manner. And Pae and THP in a concentration-dependent manner caused relaxation of the rectal ring, which is pretreated with high K+(KCl) and ACh to induce contraction. The EC50 of Pae and THP was 8.67 × 10−5 M (6.68 × 10−5-1.13 × 10−4) and 1.41 × 10−4 M (1.24 × 10−4-1.61 × 10−4) in the contraction model induced by KCl, and was 6.15 × 10−5 M (4.47 × 10−5-8.45 × 10−5), and 1.31 × 10−4 M(1.22 × 10−4-1.42 × 10−4) in the model induced by ACh, respectively. ConclusionThe intestinal absorption liquid of Guangtongxiao exerted a remarkable relaxation activity for the rectal rings, and relaxation of the smooth muscle tension might be one of the antispasmodic mechanisms of Guangtongxiao compound recipe. Also, adopting a semi-in-vivo experimental method to study the efficacy of topical external TCM recipe medicine is optimal.

Deleting Titin's C-Terminal PEVK Exons Increases Passive Stiffness, Alters Splicing, and Induces Cross-Sectional and Longitudinal Hypertrophy in Skeletal Muscle.

The Proline, Glutamate, Valine and Lysine-rich (PEVK) region of titin constitutes an entropic spring that provides passive tension to striated muscle. To study the functional and structural repercussions of a small reduction in the size of the PEVK region, we investigated skeletal muscles of a mouse with the constitutively expressed C-terminal PEVK exons 219–225 deleted, the TtnΔ219–225 model (MGI: TtnTM 2.1Mgot). Based on this deletion, passive tension in skeletal muscle was predicted to be increased by ∼17% (sarcomere length 3.0 μm). In contrast, measured passive tension (sarcomere length 3.0 μm) in both soleus and EDL muscles was increased 53 ± 11% and 62 ± 4%, respectively. This unexpected increase was due to changes in titin, not to alterations in the extracellular matrix, and is likely caused by co-expression of two titin isoforms in TtnΔ219–225 muscles: a larger isoform that represents the TtnΔ219–225 N2A titin and a smaller isoform, referred to as N2A2. N2A2 represents a splicing adaption with reduced expression of spring element exons, as determined by titin exon microarray analysis. Maximal tetanic tension was increased in TtnΔ219–225 soleus muscle (WT 240 ± 9; TtnΔ219–225 276 ± 17 mN/mm2), but was reduced in EDL muscle (WT 315 ± 9; TtnΔ219–225 280 ± 14 mN/mm2). The changes in active tension coincided with a switch toward slow fiber types and, unexpectedly, faster kinetics of tension generation and relaxation. Functional overload (FO; ablation) and hindlimb suspension (HS; unloading) experiments were also conducted. TtnΔ219–225 mice showed increases in both longitudinal hypertrophy (increased number of sarcomeres in series) and cross-sectional hypertrophy (increased number of sarcomeres in parallel) in response to FO and attenuated cross-sectional atrophy in response to HS. In summary, slow- and fast-twitch muscles in a mouse model devoid of titin’s PEVK exons 219–225 have high passive tension, due in part to alterations elsewhere in splicing of titin’s spring region, increased kinetics of tension generation and relaxation, and altered trophic responses to both functional overload and unloading. This implicates titin’s C-terminal PEVK region in regulating passive and active muscle mechanics and muscle plasticity.

Distal oblique metatarsal osteotomy technique in hallux valgus deformity: Clinical and radiological results.

Objectives This study aims to evaluate the radiological and functional outcomes of hallux valgus patients treated with distal oblique metatarsal osteotomy technique.Patients and methods Twenty-six feet of 22 patients (4 males, 18 females; mean age 46.2±18 years; range, 16 to 70 years) who were diagnosed as hallux valgus between March 2013 and April 2016 and who underwent distal oblique metatarsal osteotomy were included in this retrospective study. American Orthopedic Foot and Ankle Society/Hallux Metatarsophalangeal-Interphalangeal Scale (AOFAS/HMIS) was used for clinical and functional evaluation. The hallux valgus angle (HVA), intermetatarsal angle (IMA), distal metatarsal articular angle (DMAA), sesamoid position, first metatarsal length and forefoot bone and soft tissue width were measured for radiological evaluation.Results The mean follow-up time was 33.1±9.8 months. The AOFAS/HMIS score increased significantly postoperatively (p=0.001). In the footwear section of the AOFAS/HMIS, the median preoperative score of 5 (range, 0-5) increased to 10 (range, 5-10) at the postoperative period (p=0.001). Hallux valgus angle, IMA, DMAA, and first metatarsal length significantly decreased when compared to preoperative measurements. Forefoot bone width also decreased significantly from 9.3 cm (range, 7.5-11.5 cm) to 8.8 cm (6.8-10.3 cm) (p=0.001).ConclusionDistal oblique metatarsal osteotomy is a safe method for hallux valgus deformity. Forefoot width reduction, decrease of soft tissue tension, sesamoid reduction, and plantar fascia relaxation are the crucial benefits of this method.

Efficacy, potency and kinetics of activation process of Kv7.4 and Kv7.5 channel with novel pharmacological activators targeted for Lower Urinary Tract Syndrome (LUTS)

Among several types of Kv7 (KCNQ) voltage gated potassium channel family, Kv7.4 (KCNQ4) and Kv7.5 (KCNQ5) channels show prominent expression in smooth muscle, cardiac tissues and vasculature. In general, activation of the channel would mediate strong efflux of potassium and lead membrane potential to hyperpolarization, though the extent may depend on established potassium concentration gradient and membrane potential. Once membrane potential is hyperpolarized, it would decrease the excitability of excitable cells. Decreased excitability may reduce calcium spikes and Ca‐CaM mediated activation of myosin light chain kinase (MLCK) in smooth muscle cells. Recently, it was reported that Kv7.4 channels are highly expressed in corpus cavernosum smooth muscle cells and Kv7.5 channels in prostate smooth muscle cells, respectively. Since smooth muscle relaxation of corpus cavernosum and smooth muscle tension in prostate are in the center of pathophysiology of erectile dysfunction and LUTS, we examined the effect of novel Kv7.4 and Kv7.5 activators to the channel activation process.In HEK293 cells expressing human Kv7.4 or Kv7.5 channels, we performed whole‐cell patch clamp technique with two different voltage protocols in order to measure specific activity of the channel. For kinetic analysis of the activation process, voltage steps from –100 mV to +100 mV with 10 mV of step interval was applied. For each step, pulse duration was 3 seconds for activation process of Kv7.4 and Kv7.5 channels is rather slow. Intersweep duration was 10 seconds and holding potential was –80 mV. For measurement of time‐dependent action of the drug, 10 seconds single step with +50 mV was applied in every 30s with holding potential of –80 mV. The composition of internal solution is as following; 120 KCl, 5.37 CaCl2, 1.75 MgCl2, 10 EGTA, 10 HEPES, 4 ATP, 0.2 GTP. pH was adjusted to 7.3 using KOH and [Ca2+]free = 100 nM. Normal tyrode solution was used for external solution and drugs stocked with DMSO was diluted to corresponding concentrations with the Normal tyrode solution.We have found that URO‐K10, a novel activator, increases not only maximum conductance of the channel but also time constant of activation gate. In comparison to positive control, ML‐213, a well‐known Kv7.4 channel activator, URO‐K10 showed significant supremacy. EC50 of URO‐K10 was 0.304 ± 0.058 μM for Kv7.4 channel which is smaller than EC50 of ML‐213 (0.8 ± 0.3 μM). URO‐K10 not only increased the maximum conductance of the channel but also left‐shifted activation curve in terms of Boltzmann distribution. Half‐maximal voltage (V1/2) of Kv7.4 channel without any of the drugs was −43.03 mV whereas V1/2 of URO‐K10 activated channel was −67.65 mV, which is near the resting membrane potential of smooth muscle cells. ML‐213 activated channels showed V1/2 of −51.91 mV.Support or Funding InformationThis work was supported by the National Research Foundation of Korea, which is funded by the Ministry of Science, ICT (Information &amp; Communication Technology), and Future Planning (MSIP) of the Korean Government (2018R1A41023822 to I. So) and by the Education and Research Encouragement Fund of Seoul National University Hospital (I. So). Jung Eun Lee was supported by the BK plus program from the MSIP.

FORMING AESTHETIC COMPONENT OF VERSATILE DEVELOPMENT OF 5TH GRADE STUDENTS IN THE PROCESS OF PHYSICAL EDUCATION

The article describes the effectiveness of dance classes, which lies in the purposeful implementation of integrated use of physical and aesthetic education that “inspires”, ennobles the content and forms of classes, harmonizes the physical and spiritual qualities of children, ensures the development of body beauty, grace, elegance, aesthetic effect of appearance. The content of the aesthetic component of the program of versatile development of 5th grade students in the process of physical education has been substatiated and verified in this research. It includes classical dance, polka, school waltz, cha-cha-cha, jive and basic aerobics. In the content of the program, the following interrelated components have been identified: aesthetic, motional, ethical and gender, as dancing not only brings children aesthetic pleasure, but also helps to develop their creative abilities, desire for self-improvement and spiritual enrichment. During the pedagogical experiment we used the following methodological techniques mainly for the aesthetic component: additional guidelines and signals; exercises in the imagination; self-control and self-assessment of motor actions; aesthetic assessment and self-assessment of the quality of the exercise; demonstration of photos and movies; reproduction of motor actions of rhythmic models heard; alternating tension and muscle relaxation. Their implementation was aimed not only at achieving the maximum possible for a particular student level of mastery of dance exercises and the development of the aesthetic component, but also at the formation of a healthy, comprehensive and harmoniously developed personality of a student. Thematic construction of the series of the lessons allow to form motor actions in the process of aesthetic cognition, gradual enrichment of motor experience of students based on elements of novelty, an integrated approach to learning motor actions and the development of physical qualities. Promoting the generalization of physical qualities, in which the education of one quality is accompanied by the growth of others, that are not specially developed and providing interdisciplinary links. The importance and significance of choreography classes is explained by the fact that dance by its nature is a synthetic art form that combines spiritual-cultural and physical-cultural components, the harmony of which ensures the diverse development of children. The conducted pedagogical experiment confirmed the positive influence of dancing on the development of the aesthetic component, scientifically substantiated that dancing is a particularly effective means of multifaceted positive influence on the education of young people, which allows to recommend it for widespread implementation of physical education.

CHARACTERISTICS OF THE BIOELECTRIC ACTIVITY OF THE MASTICATORY MUSCLES IN PATIENTS WITH HEARING DEPRIVATION IN PERMANENT OCCLUSION IN THE PHYSIOLOGICAL STATE

The study of the muscles of the maxillofacial area both in normal and pathological occlusions is the area of great interest, since muscle function is an indicator of complex functional relationships of the dento-mandibular system. Hearing impaired patients have many features related to the functional features of the maxillofacial area due to the slight or complete lack of use of facial muscles during speech or through the use of sign language. Hearing impaired children have 100% of bite pathology.&#x0D; The functional state of chewing and temporal muscles in schoolchildren with hearing loss in constant bite at rest was studied. Twenty-five hearing impaired students with permanent dentistry were studied at Poltava Special Boarding School for Deaf Children, who formed the study group. Among them, there were 13 women (62.5%) and 12 men (37.5%). The mean age was 18.7 ± 1.31 years. The control group used the data of the study of patients with constant physiological bite without hearing disorders, determined by M. I. Dmytrenko. The average age was 21.3 ± 1.25 years.&#x0D; The bioelectric activity of the chewing muscles was examined on an electromyographic complex. The average values of oscillation amplitude (μV) of muscle biopotential on both sides were determined. Muscle biopotentials were recorded for five seconds in a state of physiological calm with closed lips.&#x0D; The results show that all indicators of PD of chewing muscles in a state of physiological rest are almost 2 times higher (p˂0,05) in comparison with those of patients with normal hearing and physiological bite. The work of the temporal muscles in schoolchildren with hearing loss is characterized by symmetry. There is also greater electrical activity of the temporal muscle than the masticatory muscles at rest, unlike normal hearing patients.&#x0D; All patients with hearing impairment had 100% prevalence of dental anomalies. Biopotential of chewing muscle of I class. for angle was 2.7 times higher than in patients with the control group. The biopotential of the temporalis muscle in the ICE was 1.8 times higher (p˂0.05), which indicates a constant tension or insufficient muscle relaxation in patients with ICE. In patients with hearing loss of II class. for angle, the average value of the biopotential of the chewing muscle was 2.3 times higher than in patients in 2 group, the temporal muscle was 1.5 times higher.

The effect of in situ‐formed copolymers on the morphology of reactive poly(phenylene ether)/poly(amide‐6) blends

AbstractPoly(phenylene ether) (PPE)/poly(amide‐6) (PA6) blends are examined in light of the information provided by two‐dimensional chromatography and chemorheology. Chromatography provides a snapshot of the blend composition in the finished material, while rheology presents us with a direct insight into the reactions taking place in the melt. Block copolymer formation is chromatographically confirmed for the blends prepared with a coupling agent, but also for the blend prepared without any coupling agent. No co‐continuous morphology is observed by scanning electron microscope. Instead, a coarse structure of PPE droplets in the PA6 matrix is obtained for the blend prepared without coupling agent. This is explained by the combined effects of the low viscosity of PA6 and the inherently formed copolymers. The PPE domains are smaller in the blends prepared with the coupling agents. Their size is correlated with the copolymer formation, surface tension, and interphase relaxation time. The data evidence a complex system where reactions resulting in the formation of copolymer via coupling or grafting take place together with the extension of the PPE and condensation growth of the PA6 polymers.

Wingless counteracts epithelial folding by increasing mechanical tension at basal cell edges in Drosophila.

The modulation of mechanical tension is important for sculpturing tissues during animal development, yet how mechanical tension is controlled remains poorly understood. In Drosophila wing discs, the local reduction of mechanical tension at basal cell edges results in basal relaxation and the formation of an epithelial fold. Here, we show that Wingless, which is expressed next to this fold, promotes basal cell edge tension to suppress the formation of this fold. Ectopic expression of Wingless blocks fold formation, whereas the depletion of Wingless increases fold depth. Moreover, local depletion of Wingless in a region where Wingless signal transduction is normally high results in ectopic fold formation. The depletion of Wingless also results in decreased basal cell edge tension and basal cell area relaxation. Conversely, the activation of Wingless signal transduction leads to increased basal cell edge tension and basal cell area constriction. Our results identify the Wingless signal transduction pathway as a crucial modulator of mechanical tension that is important for proper wing disc morphogenesis.

Mass transport of SDS and AOT solutions during a rapid surface expansion: Relaxation of surface tension

Abstract Surface tension (ST) relaxations are influential in industrial processes that are characterized by substantial surface deformations. Despite this, the dynamics of surfactant adsorption onto a dilating surface is still unclear. Recently, the ST relaxation of a non-ionic surfactant (TX-100) was reported (Lin et al. (2017) [17]), but little is known about the behavior of ionic surfactants. In this study, the relaxations of ST and surface dilational rates (λ) of ionic aerosol-OT (AOT) and sodium dodecyl sulfate (SDS) solutions were investigated by monitoring a continuously expanding bubble using a pendant bubble tensiometer. The data showed that during the rapid bubble expansion, ST of AOT solutions increased with time, while that of SDS changed negligibly. This implied that the mass transfer rate of AOT molecules from bulk to the bubble surface during expansion (at λ

Bakera: Tradition of medicinal plants utilization for therapy, prevention and recovery of diseases in Jailolo Sultanate custom society, Indonesia

Abstract. Syahdar SA, Tamalene MN, Hasan S. 2019. Bakera: tradition of medicinal plants utilization for therapy, prevention and recovery of diseases in Jailolo Sultanate custom s­ociety, Indonesia. Asian J Ethnobiol 2: 41-47. Indonesia is well-known as the source of tropical plants that are very useful for treating various diseases. In addition, there are also various traditional knowledge of herbal utilization in many societies. The people of eastern part in North Maluku Utara Province, the Jailolo Sultanate Society of Halmahera Island, which consists of four original tribes: Gamkonora, Tobaru, Sahu, and Wayoli, still use traditional medicine to treat diseases. Their tradition called “Baker” is similar to the ‘Spa’ in modern urban societies. Bakera as one of local geniuses in medical field has become entrepreneurial interest, especially for those running the spa business. Medically, plants used in Bakera have been proven to have positive effects on health. This data may enrich other data on the wealth and diversity, as well as knowledge on medicinal plants of Indonesian communities. The research used emic and etic approaches. Data was analyzed descriptively, data presentation, data reduction and data verification, data validity check. Informants of the research were eight people, selected using Purposive Sampling Technique. Bakera can be used in postpartum treatment as well as to treat sore, malaria and liver. As a whole, the use of nine different plant species for Bakera consists of medicinal and spice plants. There are three plant species found that often cultivate in the yard. Bakera has thermotherapy and aromatherapy effects that contribute to Bakera effectiveness. Thermotherapy could pacify muscle tension, lose weight, increase blood circulation, reduce tension headache, autoimmunity, and relaxation. In addition, plants used have immunostimulant, antiseptic, and antiphlogistic effects.

Interfacial characteristics and the stability mechanism of a dispersed particle gel (DPG) three-phase foam

Dispersed particle gel (DPG) was added to foams to obtain a more stable foam system: the DPG three-phase foam. Film drainage, interfacial rheology, and stability mechanism of the DPG three-phase foam were studied. The foam volume of the DPG three-phase foam was slightly higher than that of the traditional foam, and the half-decay time was five times that of the traditional foam. The results of film drainage show that DPG particles mainly improve the stability of thin films, i.e., the ability to bond with and capture water. Interfacial characteristics were investigated by the interfacial tension relaxation method. DPG particles slowed down the overall molecular relaxation process of the foam system, which enhanced the viscoelasticity and the mechanical strength of the interface. The stability mechanism can be explained as follows. The adsorption between DPG particles and Tetradecyl hydroxyl sulfobetaine (THSB) occurs owing to the hydrophobic attractive interaction. Therefore, DPG particles aggregate at the interface to form a shell structure, which increases the mechanical strength of the thin film by its low relaxation process; thus, a stable interface is formed, and the stability of the foam is enhanced.

A Pilot Study on Biaxial Mechanical, Collagen Microstructural, and Morphological Characterizations of a Resected Human Intracranial Aneurysm Tissue

Intracranial aneurysms (ICAs) are focal dilatations that imply a weakening of the brain artery. Incidental rupture of an ICA is increasingly responsible for significant mortality and morbidity in the American's aging population. Previous studies have quantified the pressure-volume characteristics, uniaxial mechanical properties, and morphological features of the human aneurysms. In this pilot study, for the first time, we comprehensively quantified the mechanical, collagen fiber microstructural, and morphological properties of a resected human posterior inferior cerebellar artery aneurysm. The tissue from the dome of a right posterior inferior cerebral aneurysm was first mechanically characterized using biaxial tension and stress relaxation tests. Then, the load-dependent collagen fiber architecture of the aneurysm tissue was quantified using an in-house polarized spatial frequency domain imaging system. Finally, optical coherence tomography and histological procedures were used to quantify the tissue's microstructural morphology. Mechanically, the tissue was shown to exhibit hysteresis, a nonlinear stress-strain response, and material anisotropy. Moreover, the unloaded collagen fiber architecture of the tissue was predominantly aligned with the testing Y-direction and rotated towards the X-direction under increasing equibiaxial loading. Furthermore, our histological analysis showed a considerable damage to the morphological integrity of the tissue, including the lack of elastin, intimal delamination, and calcium deposition. This pilot study has provided new insights into the multiscale properties of aneurysm tissues. The method presented herein, together with the novel results, can be used to develop accurate constitutive models to use in computational models of the aneurysm hemodynamics, growth, and remodeling.

Impact of crosslink heterogeneity on extracellular matrix mechanics and remodeling

Mechanical interactions between cells and the extracellular matrix (ECM) lead to the formation of biophysical cues, notably in the form of cell-generated tension, stiffness, and concentration profiles in the ECM. Fibrillar ECMs have nonlinear stiffnesses, linked to the reorientation of fibers under stress and strain, and nonelastic properties, resulting from the force-induced unbinding of transient bonds (crosslinks) that interconnect fibers. Mechanical forces generated by cells can lead to local ECM stiffening and densification. Cell tension is also propagated through the ECM network. The underlying factors that regulate the relative emergence of these signals are not well understood. Here, through computational simulations of 3D ECM fiber networks, we show that the composition of ECM crosslinks is a key determinant of the degree of densification and stiffening that can be achieved by cell-generated forces. This also regulates the sustainability of tensions propagated through the ECM. In particular, highly transient force-sensitive crosslinks promote nonelastic densification and rapid tension relaxation, whereas permanent crosslinks promote nonlinear stiffening and stable tension profiles. A heterogeneous population of crosslinks with different unbinding kinetics enables ECMs to exhibit accumulation, tension propagation, and stiffening simultaneously in response to mechanical interactions with cells.

The relation between sarcomere energetics and the rate of isometric tension relaxation in healthy and diseased cardiac muscle

Full muscle relaxation happens when [Ca2+] falls below the threshold for force activation. Several experimental models, from whole muscle organs and intact muscle down to skinned fibers, have been used to explore the cascade of kinetic events leading to mechanical relaxation. The use of single myofibrils together with fast solution switching techniques, has provided new information about the role of cross-bridge (CB) dissociation in the time course of isometric force decay. Myofibril’s relaxation is biphasic starting with a slow seemingly linear phase, with a rate constant, slow kREL, followed by a fast mono-exponential phase. Sarcomeres remain isometric during the slow force decay that reflects CB detachment under isometric conditions while the final fast relaxation phase begins with a sudden give of few sarcomeres and is then dominated by intersarcomere dynamics. Based on a simple two-state model of the CB cycle, myofibril slow kREL represents the apparent forward rate with which CBs leave force generating states (gapp) under isometric conditions and correlates with the energy cost of tension generation (ATPase/tension ratio); in short slow kREL ~ gapp ~ tension cost. The validation of this relationship is obtained by simultaneously measuring maximal isometric force and ATP consumption in skinned myocardial strips that provide an unambiguous determination of the relation between contractile and energetic properties of the sarcomere. Thus, combining kinetic experiments in isolated myofibrils and mechanical and energetic measurements in multicellular cardiac strips, we are able to provide direct evidence for a positive linear correlation between myofibril isometric relaxation kinetics (slow kREL) and the energy cost of force production both measured in preparations from the same cardiac sample. This correlation remains true among different types of muscles with different ATPase activities and also when CB kinetics are altered by cardiomyopathy-related mutations. Sarcomeric mutations associated to hypertrophic cardiomyopathy (HCM), a primary cardiac disorder caused by mutations in genes encoding sarcomeric proteins, have been often found to accelerate CB turnover rate and increase the energy cost of myocardial contraction. Here we review data showing that faster CB detachment results in a proportional increase in the energetic cost of tension generation in heart samples from both HCM patients and mouse models of the disease.

Impact of PDMS surface treatment in cell-mechanics applications

As a widely used elastomer in cell mechanics studies, PDMS is exposed to a variety of surface treatments during cell culture preparation. Considering its viscoelastic nature in particular, effects of the aforementioned treatments on PDMS mechanical behaviour, especially at the relevant length scale of 100 μm, received limited attention. This is despite the fact that significant errors were reported in the quantification of cellular traction forces as a result of minute changes in PDMS mechanical properties. Hence, the effects of plasma oxidation, sterilization and incubation on PDMS modulus of elasticity, relaxation modulus and Poisson's ratio are studied here through tension and stress relaxation tests, with the results of the latter interpreted via the linear viscoelastic formulation. It is observed that although significant deviations from the properties of untreated PDMS are measured through this cycle of surface treatment, properties of untreated PDMS are almost recovered following incubation in cell medium. For example, the modulus of elasticity of treated PDMS was found to be 6% smaller than that of the untreated PDMS. The corresponding deviation was <3% and <1% for the relaxation modulus and time-averaged Poisson's ratio, respectively. The rate of change of the Poisson's ratio with time was also found to be reduced at the end of incubation process in cell medium. As a result, viscoelastic properties of untreated PDMS can safely be used within the error margins provided by this work.

Simultaneous Regulation of Cytokinetic Furrow and Nucleus Positions by Cortical Tension Contributes to Proper DNA Segregation during Late Mitosis.

Coordinating mitotic spindle and cytokinetic furrow positioning is essential to ensure proper DNA segregation. Here, we present a novel mechanism, which corrects DNA segregation defects due to cytokinetic furrow mispositioning during the first division of C.elegans embryos. Correction of DNA segregation defects due to an abnormally anterior cytokinetic furrow relies on the concomitant and opposite displacements of the furrow and of the anterior nucleus toward the posterior and anterior poles of the embryo, respectively. It also coincides with cortical blebbing and an anteriorly directed cytoplasmic flow. Although microtubules contribute to nuclear displacement, relaxation of an excessive tension atthe anterior cortex plays a central role in the correction process and simultaneously regulates cytoplasmic flow as well as nuclear and furrow displacements. This work thus reveals the existence of a so-far uncharacterized correction mechanism, which is critical to correct DNA segregation defects due to cytokinetic furrow mispositioning.

Investigation on failure properties and constitutive modeling of EPDM used for pulse separation device

In order to characterize the rate-dependent deformation-failure behavior of pulse separation device (PSD) of ethylene propylene diene monomer (EPDM), uniaxial constant rate tension, variable rate tension, and stress relaxation experiments were conducted for EPDM in a universal testing machine. It was found that the deformation-failure behavior of EPDM was dependent on the applied strain rates. An improved hyper-viscoelastic constitutive model with an energy limiter (in which the constant energy limiter was replaced by a rate-dependent energy limiter) was proposed to predict the rate-dependent deformation-failure behavior of EPDM under quasi-static loading. The proposed model was first calibrated by fitting it (based on the least squares method) to the data obtained from uniaxial constant rate tension experiments and then further examined by the data obtained from variable rate tension and stress relaxation experiments. The comparative results revealed that the constitutive model with a rate-dependent energy limiter predicted the rate-dependent deformation-failure behavior of EPDM under finite deformation and quasi-static loadings very well.

Short-time xylem tension relaxation prevents vessel refilling and alleviates cryo-fixation artifacts in diffuse-porous Carpinus tschonoskii and Cercidiphyllum japonicum.

Xylem tension relaxation is an important procedure that closely resembles the in vivo xylem water distribution when measuring conductivity or observing water distribution of plant tissue samples by cryo-scanning electron microscopy (cryo-SEM). Recent studies have shown that partial xylem embolism occurs when samples under tension are cut under water and that gas-filled vessels are refilled during tension relaxation. Furthermore, the frequency of gas-filled vessels has been reported to increase in samples without tension relaxation before cryo-fixation by liquid nitrogen, particularly in samples with significant tension. Here, we examined the effect of tension relaxation on these artifacts in Carpinus tschonoskii and Cercidiphyllum japonicum using magnetic resonance imaging. We observed that xylem embolism rarely occurs in bench-dried samples cut under water. In both species, a small portion of the xylem was refilled within ~1h after tension relaxation. Cryo-SEM observations revealed that short-time (<1h) xylem tension relaxation decreases the frequency of gas-filled vessels in samples frozen after xylem tension relaxation regardless of the water potential compared with that in samples frozen without rehydration in both species. Therefore, short-time tension relaxation is necessary to retain xylem water distribution during sample preparation against artifacts.

Xylem Water Distribution in Woody Plants Visualized with a Cryo-scanning Electron Microscope.

A scanning electron microscope installed cryo-unit (cryo-SEM) allows specimen observation at subzero temperatures and has been used for exploring water distribution in plant tissues in combination with freeze fixation techniques using liquid nitrogen (LN2). For woody species, however, preparations for observing the xylem transverse-cut surface involve some difficulties due to the orientation of wood fibers. Additionally, higher tension in the water column in xylem conduits can occasionally cause artifactual changes in water distribution, especially during sample fixation and collection. In this study, we demonstrate an efficient procedure to observe the water distribution within the xylem of woody plants in situby using a cryostat and cryo-SEM. At first, during sample collection, measuring the xylem water potential should determine whether high tension is present in the xylem conduits. When the xylem water potential is low (< ca. -0.5 MPa), a tension relaxation procedure is needed to facilitate better preservation of the water status in xylem conduits during sample freeze fixation. Next, a watertight collar is attached around the tree stem and filled with LN2for freeze fixation of the water status of xylem. After harvesting, care should be taken to ensure that the sample is preserved frozen while completing the procedures of sample preparation for observation. A cryostat is employed to clearly expose the xylem transverse-cut surface. In cryo-SEM observations, time adjustment for freeze-etching is required to remove frost dust and accentuate the edge of the cell walls on the viewing surface. Our results demonstrate the applicability of cryo-SEM techniques for the observation of water distribution within xylem at cellular and subcellular levels. The combination of cryo-SEM with non-destructive in situ observation techniques will profoundly improve the exploration of woody plant water flow dynamics.