Passive Tension Research Articles

Residual force enhancement is reduced in permeabilized fiber bundles from mdm muscles.

Residual force enhancement (RFE) is the increase in steady-state force after active stretch relative to the force during isometric contraction at the same final length. The muscular dystrophy with myositis (mdm) mutation in mice, characterized by a small deletion in N2A titin, has been proposed to prevent N2A titin-actin interactions so that active mdm muscles are more compliant than wild type (WT). This decrease in active muscle stiffness is associated with reduced RFE. We investigated RFE in permeabilized soleus (SOL) and extensor digitorum longus (EDL) fiber bundles from WT and mdm mice. On each fiber bundle, we performed active and passive stretches from an average sarcomere length of 2.6-3.0 µm at a slow rate of 0.04 µms-1, as well as isometric contractions at the initial and final lengths. One-way ANOVA showed that SOL and EDL fiber bundles from mdm mice exhibited significantly lower RFE than WT mice (P<0.0001). This result is consistent with previous observations in single myofibrils and intact muscles. However, it contradicts the results from a previous study that appeared to show that compensatory mechanisms could restore titin force enhancement in single fibers from mdm psoas. We suggest that RFE measured previously in mdm single fibers was an artifact of the high variability in passive tension found in degenerating fibers, which begins after ∼24 days of age. The results are consistent with the hypothesis that RFE is reduced in mdm skeletal muscles owing to impaired Ca2+-dependent titin-actin interactions resulting from the small deletion in N2A titin.

A nonlinear adaptive fuzzy controller with signal transmission delay compensation for steel rope tension active control of mining hoists

The double-rope winding hoists have been widely used in the ultra-deep mines. However, there exists tension imbalance issue on two steel rope of the double-rope winding hoist. The passive tension control method is not ideal in both adjust accuracy and response speed. Therefore, a novel hybrid control method is proposed for active control of two steel rope tensions considering the wireless transmission delay of steel rope tension signal, nonlinear uncertainties, and external disturbance. First, a signal transmission delay compensator is designed to obtain the observed feedback signal and other correlated variables. It is worth mentioning that the effectiveness of designed signal transmission delay compensator is verified not only in theory and simulation but also by experiments. Then, a hybrid controller that combines the adaptive backstepping theory and adaptive fuzzy algorithm is designed to obtain the active control output of two steel rope tensions. It is theoretically depicted that the proposed nonlinear adaptive fuzzy controller combined with the signal transmission delay compensator not only achieves good robust performance on model uncertainty but also improves the closed-loop system response rate. Moreover, the proposed controller can compensate external disturbance and suppress chattering caused by ordinary methods based on backstepping technology. The stability of the integrated closed-loop system with the hybrid controller is proved on the basis of Lyapunov theory. In order to demonstrate the feasibility and effectiveness of the proposed nonlinear adaptive fuzzy controller combined with the signal transmission delay compensator, a double-rope winding hoisting simulated test device is set up for experimental investigation. Then, contrast experiments with the traditional proportion–integration, adaptive backstepping controller, and the proposed controller are conducted on the test device. Experimental results verify the superior of the proposed nonlinear adaptive fuzzy controller combined with the signal transmission delay compensator on tension control of two steel ropes for the double-rope winding hoist.

Prolonged Exposure to Intestinal Edemagenic Stress Decreases Mesenteric Lymphatic Contractility

Mesenteric lymphatic vessels (MLVs) are the primary route for removal of excess intestinal interstitial fluid. Lymphatic pumping, the virtue of the intrinsic contractility of lymphatic muscle, is necessary for active lymph transport to the venous circulation and thus resolution of interstitial edema. Acute exposure to edemagenic stress has been reported to increase contractility and pumping of MLVs. However, our recent studies revealed that when exposure to edemagenic stress is prolonged, lymphatic contraction frequency decreases and pump failure ensues. It is unknown how the ability of lymphatic muscle to generate active tension is affected in these maladapted MLVs. Therefore, the purpose of the present study was to evaluate our hypothesis that prolonged exposure to edemagenic stress decreases lymphatic muscle contractility.Male Sprague Dawley rats underwent midline laparotomy with 3‐day exposure to either venous hypertension (VHT; induced by coarctation of superior mesenteric vein), fluid overload (HD; induced by daily IV infusion of 80 ml/kg lactated Ringer’s saline), or neither (SHAM; no additional intervention). In isometric biomechanics studies, MLVs were mounted on a wire myograph and perfused with warm APSS. Vessel rings were incrementally stretched, stimulated with substance P (1 µM) in 60 mM K+‐APSS (SP K‐APSS), followed by wash out with APSS. This sequence was repeated and the following steady state tensions were recorded at each level of stretch: unstimulated total tension (passive stretch, in APSS), stimulated total tension (SP K‐APSS), and passive tension (Ca++‐free APSS, at the end of the experiment). The circumferential length at the level of stretch yielding optimal delta tension (= stimulated total tension ‐ unstimulated total tension) for each vessel was identified as Lmax. Additionally, unstimulated active tension (= unstimulated total tension ‐ passive tension) and stimulated active tension (= stimulated total tension ‐ passive tension) were calculated.Vessels from VHT and SHAM groups yielded nearly identical length‐tension relationships. However, compared to SHAM and VHT vessels, HD vessels generated significantly lower tension across all indices: unstimulated total tension, stimulated total tension, passive tension, unstimulated active tension, and stimulated active tension. At optimal stretch (Lmax), the delta tension was lower in HD vessels than SHAM or VHT vessels.Consistent with findings of the previous studies, prolonged exposure to intestinal edemagenic stress induced mesenteric lymphatic pump failure in VHT and HD vessels. However, lymphatic muscle contractility was reduced only in HD vessels. Taken together, these findings suggest that peri‐ and post‐oprative fluid therapy in major surgery patients receiving fluid therapy may lead to mesenteric lymphatic maladaptation. The consequential decrease in intestinal lymph drainage would then contribute to delayed resolution of intestinal edema, increased morbidity and extended hospital stays.

Relaxing Effects of Paracetamol on Uterine Spontaneous Contraction in Rats in Vitro

Aim: Paracetamol is a commonly used drug in acute and chronic pain. It is known that paracetamol, which is a pain reliever and antipyretic drug, is safe to use during pregnancy. The aim of this study was to investigate the effects of paracetamol on the uterine smooth muscle contraction- relaxation mechanism in female rats in diestrus.Material and Methods: Wistar-albino intact female rats were used in the study. Longitudinal strips of myometrium obtained from animals at the diestroeus stage. Stripes were suspended in an isolated organ bath containing crebs solution under 1 g passive tension. After the regulation period, paracetamol were added non-cumulatively at 1000μM and 2000μM concentrations. Before and after the application, the area under the curve (AUC) and peak to peak (p-p) values were normalized as % change.Results: Paracetamol caused a statistically significant decrease in p-p and area under the curve parameters of spontaneous uterine contractions at 1000 and 2000 μM doses (p &amp;lt;0.001).Conclusion: Paracetamol causes uterine relaxation by inhibiting uterine contraction. This effect should be taken into account in clinical use.

Factors correlated with the optimal tension for arthroscopic rotator cuff repair using Grasper Tensioning Attachment.

Little is known about the optimal tension in arthroscopic rotator cuff repair (ARCR). This study aimed to identify preoperative, intraoperative, and postoperative factors that correlate with the tension in ARCR and to determine the optimal intraoperative tension using Grasper Tensioning Attachment, a tension meter attached to the common arthroscopic surgical grasper. This study included 63 patients with a mean age at surgery of 65.3 years (range, 45-83 years) who underwent ARCR. The mean follow-up period was 24.1 months (range, 24-28 months). We investigated the patients' demographic data, Japanese Orthopaedic Association score, DeOrio and Cofield classification, and Goutallier stage of the supraspinatus and infraspinatus muscles. We also evaluated cuff integrity based on the Sugaya classification via magnetic resonance imaging. The free edge of the torn retracted tendon was grasped, and the passive tension to the footprint was then measured with Grasper Tensioning Attachment with the arm at the side. The anteroposterior (AP) and mediolateral (ML) diameters were also measured. The preoperative Goutallier stage of the supraspinatus muscle was stage 0 in 7 cases, stage 1 in 34, stage 2 in 20, and stage 3 in 2. The mean intraoperative rotator repair tension was 10.0 ± 2.5 N (range, 7.5-17 N). The mean AP diameter of the rotator cuff tear was 22 ± 10 mm (range, 8-50 mm), and the mean ML diameter was 24 ± 10 mm (range, 10-50 mm). Age, DeOrio and Cofield classification, Goutallier stage, AP diameter, and ML diameter correlated with rotator repair tension. The rotator repair tension in Sugaya classification type III or IV cases (n = 12, 11.4 ± 2.4 N) was significantly larger than that in type I or II cases (n = 51, 9.7 ± 2.4 N; P = .03). Tension ≥ 10 N as a cutoff value from receiver operating characteristic curve analysis was a risk factor for poor cuff integrity (95% confidence interval, 0.53-0.88). Rotator repair tension ≥ 10 N was a risk factor for poor cuff integrity. Thus, care should be taken when performing intraoperative procedures and administering postoperative regimens.

Procedures for obtaining muscle physiology parameters during a gracilis free-functioning muscle transfer in adult patients with brachial plexus injury

A complete understanding of muscle mechanics allows for the creation of models that closely mimic human muscle function so they can be used to study human locomotion and evaluate surgical intervention. This includes knowledge of muscle–tendon parameters required for accurate prediction of muscle forces. However, few studies report experimental data obtained directly from whole human muscle due to the invasive nature of these experiments. This article presents an intraoperative, in vivo measurement protocol for whole muscle–tendon parameters that include muscle–tendon unit length, sarcomere length, passive tension, and active tension in response to external stimulation. The advantage of this protocol is the ability to obtain these rare experimental data in situ in addition to muscle volume and weight since the gracilis is also completely removed from the leg. The entire protocol including the surgical steps for gracilis harvest takes ~ 3 h. Actual testing of the gracilis where experimental data is measured takes place within a 30-min window during surgery.

How octopus arm muscle contractile properties and anatomical organization contribute to arm functional specialization.

Octopus arms are highly flexible structures capable of complex motions and are used in a wide repertoire of behaviors. Movements are generated by the coordinated summation of innervation signals to packed arrays of muscles oriented in different directions and moving based on their anatomical relationships. In this study, we investigated the interplay between muscle biomechanics and anatomical organization in the Octopus vulgaris arm to elucidate their role in different arm movements. We performed isometric and isotonic force measurements on isolated longitudinal and transverse arm muscles and showed that longitudinal muscles have a higher rate of activation and relaxation, lower twitch-to-tetanus ratio and lower passive tension than transverse muscles, thus prompting their use as faster and slower muscles, respectively. This points to the use of longitudinal muscles in more graded responses, such as those involved in precise actions, and transverse muscles in intense and sustained actions, such as motion stabilization and posture maintenance. Once activated, the arm muscles exert forces that cause deformations of the entire arm, which are determined by the amount, location, properties and orientation of their fibers. Here, we show that, although continuous, the arm manifests a certain degree of morphological specialization, where the arm muscles have a different aspect ratio along the arm. This possibly supports the functional specialization of arm portions observed in various motions, such as fetching and crawling. Hence, the octopus arm as a whole can be seen as a 'reservoir' of possibilities where different types of motion may emerge at the limb level through the co-option of the muscle contractile properties and structural arrangement.

GSK-3β Localizes to the Cardiac Z-Disc to Maintain Length Dependent Activation.

Altered kinase localization is gaining appreciation as a mechanism of cardiovascular disease. Previous work suggests GSK-3β (glycogen synthase kinase 3β) localizes to and regulates contractile function of the myofilament. We aimed to discover GSK-3β's in vivo role in regulating myofilament function, the mechanisms involved, and the translational relevance. Inducible cardiomyocyte-specific GSK-3β knockout mice and left ventricular myocardium from nonfailing and failing human hearts were studied. Skinned cardiomyocytes from knockout mice failed to exhibit calcium sensitization with stretch indicating a loss of length-dependent activation (LDA), the mechanism underlying the Frank-Starling Law. Titin acts as a length sensor for LDA, and knockout mice had decreased titin stiffness compared with control mice, explaining the lack of LDA. Knockout mice exhibited no changes in titin isoforms, titin phosphorylation, or other thin filament phosphorylation sites known to affect passive tension or LDA. Mass spectrometry identified several z-disc proteins as myofilament phospho-substrates of GSK-3β. Agreeing with the localization of its targets, GSK-3β that is phosphorylated at Y216 binds to the z-disc. We showed pY216 was necessary and sufficient for z-disc binding using adenoviruses for wild-type, Y216F, and Y216E GSK-3β in neonatal rat ventricular cardiomyocytes. One of GSK-3β's z-disc targets, abLIM-1 (actin-binding LIM protein 1), binds to the z-disc domains of titin that are important for maintaining passive tension. Genetic knockdown of abLIM-1 via siRNA in human engineered heart tissues resulted in enhancement of LDA, indicating abLIM-1 may act as a negative regulator that is modulated by GSK-3β. Last, GSK-3β myofilament localization was reduced in left ventricular myocardium from failing human hearts, which correlated with depressed LDA. We identified a novel mechanism by which GSK-3β localizes to the myofilament to modulate LDA. Importantly, z-disc GSK-3β levels were reduced in patients with heart failure, indicating z-disc localized GSK-3β is a possible therapeutic target to restore the Frank-Starling mechanism in patients with heart failure.

Nicotinic-acid derivative BGP-15 improves diastolic function in a rabbit model of atherosclerotic cardiomyopathy.

The small molecule BGP-15 has been reported to alleviate symptoms of heart failure and improve muscle function in murine models. Here, we investigated the acute and chronic effects of BGP-15 in a rabbit model of atherosclerotic cardiomyopathy. Rabbits were maintained on standard chow (control) or atherogenic diet (hypercholesterolemic) for 16 weeks. BGP-15 was administered intravenously (once) or orally (for 16 weeks), to assess acute and chronic effects. Cardiac function was evaluated by echocardiography, endothelium-dependent vasorelaxation was assessed and key molecules in the protein kinase G (PKG) pathway were examined by enzyme-linked immunosorbent assay (ELISA) and western blot. Passive force generation was investigated in skinned cardiomyocytes. Both acute and chronic BGP-15 treatments improved the diastolic performance of the diseased heart. However, vasorelaxation and serum lipid markers were unaffected. Myocardial cyclic guanosine monophosphate (cGMP) levels were elevated in the BGP-15-treated group, along with preserved PKG activity and increased phospholamban Ser16-phosphorylation. PDE5 expression decreased in the BGP-15-treated group and PDE1 was inhibited. Cardiomyocyte passive tension reduced in BGP-15-treated rabbits, the ratio of titin N2BA/N2B isoforms increased and PKG-dependent N2B-titin phosphorylation elevated. BGP-15 treatment improves diastolic function, reduces cardiomyocyte stiffness and restores titin compliance in a rabbit model of atherosclerotic cardiomyopathy by increasing the activity of the cGMP-PKG pathway. As BGP-15 has been proven to be safe, it may be clinically useful in the treatment of diastolic dysfunction.

Microtubules maintain passive tension and myofibril formation in developing cardiomyocytes

During development, cardiomyocytes (CMs) undergo a hypertrophic growth phase to generate load for the heart to pump sufficient blood. However, in the early stages of pathological hypertrophy, stress-induced signal transduction promotes the addition of new contractile units through poorly understood mechanisms to maintain tensional homeostasis. Microtubules provide mechanical resistance in CMs; however, little is known about their role in maintaining tensional homeostasis in response to development and sarcomeric remodeling.

Functional and structural differences between skinned and intact muscle preparations.

Myofilaments and their associated proteins, which together constitute the sarcomeres, provide the molecular-level basis for contractile function in all muscle types. In intact muscle, sarcomere-level contraction is strongly coupled to other cellular subsystems, in particular the sarcolemmal membrane. Skinned muscle preparations (where the sarcolemma has been removed or permeabilized) are an experimental system designed to probe contractile mechanisms independently of the sarcolemma. Over the last few decades, experiments performed using permeabilized preparations have been invaluable for clarifying the understanding of contractile mechanisms in both skeletal and cardiac muscle. Today, the technique is increasingly harnessed for preclinical and/or pharmacological studies that seek to understand how interventions will impact intact muscle contraction. In this context, intrinsic functional and structural differences between skinned and intact muscle pose a major interpretational challenge. This review first surveys measurements that highlight these differences in terms of the sarcomere structure, passive and active tension generation, and calcium dependence. We then highlight the main practical challenges and caveats faced by experimentalists seeking to emulate the physiological conditions of intact muscle. Gaining an awareness of these complexities is essential for putting experiments in due perspective.

Optimal Wire Myography Normalization for the Rat Dorsal Penile, Internal Pudendal and Internal Iliac Arteries

In functional arterial studies using wire myography, the determination of a vessel’s standardized normalization factor (factor k) is an essential step to ensure optimal contraction and relaxation by the arteries when stimulated with their respective vasoactive agents and to obtain reproducible results. The optimal factor k for several arteries have been determined; however, the optimal initial tension and factor k for the arteries involved in erection remains unknown. Hence, in the present study we set out to determine the optimal factor k for the internal iliac artery, proximal and distal internal pudendal artery (IPA), and dorsal penile artery. After isolating, harvesting, and mounting the arteries from male Sprague-Dawley rats on a multi wire myograph, we tested arterial responsivity to high K+-stimulation when the factor k was set at 0.7, 0.8, 0.85, 0.9, 0.95, 1.0, 1.1, and 1.2 to determine the factor k setting that results in the greatest K+-induced active force production for each vessel type. The data showed the optimal factor k is 0.90-0.95 for the dorsal penile, distal internal pudendal and internal iliac arteries while it is 0.85-0.90 for proximal internal pudendal artery. These optimal values corresponded to initial passive tension settings of 1.10±0.16 - 1.46±0.23, 1.28±0.20 - 1.69±0.34, 1.03±0.27 - 1.33±0.31, and 1.33±0.31 - 1.77±0.43 mN/mm for the dorsal penile, distal IP, proximal IP, and internal iliac arteries, respectively.

Identification of the domains within the N2A region of titin that regulate binding to actin

Titin, the largest muscle protein, plays an important role in passive tension, sarcomeric integrity and cell signaling within the muscle. Recent work has also highlighted a role for titin in active muscle and the N2A region found in skeletal muscle titin and in some isoforms of cardiac titin has been linked to this function. The N2A region is a multi-domain region composed of four immunoglobulin domains (I80–I83) and a disordered region called the insertion sequence. Previously, our lab has shown that the N2A region binds F-actin in a calcium dependent manner, but it is not known which domains within this region are critical for this binding to occur. In this work, we have used co-sedimentation to demonstrate that only constructs containing the I80 domain are capable of binding F-actin. In addition, binding was only observed in constructs containing at least 3 immunoglobulin domains suggesting a length-dependence to binding. Finally, the calcium-dependence of N2A binding is lost when I83 is not present, consistent with the calcium stabilization that has been reported for this domain. Based on these results, we propose that I80 is critical for initiating binding to F-actin and that I83 is responsible for the calcium dependence.

Abstract 11592: Glycogen Synthase Kinase 3β Localizes to the Z-Disc to Maintain Length Dependent Activation

Glycogen Synthase Kinase 3β (GSK-3β) can modulate myofilament function in vitro . However, it’s in vivo role, mechanism, and translational relevance are unknown, which we investigated here using inducible cardiomyocyte specific GSK-3β KO mice. Compared to tamoxifen-treated GSK-3β fl/fl Cre- mice (Con), skinned myocytes from KO mice had reduced calcium sensitivity at long sarcomere lengths (SL = 2.2 μm), but there were no differences at short SL (~1.9 μm). Thus, myocytes from KO mice did not sensitize to calcium with stretch, a mechanism called length dependent activation (LDA) that underlies the organ-level Frank-Starling law. LDA has been attributed to (1) phosphorylation of myofilament proteins, (2) altered lattice-spacing, and (3) changes to titin’s elastic properties. Using mass spectrometry and small energy x-ray diffraction we ruled out the first two mechanisms, however we did find that GSK-3β KO myocytes had decreased passive tension – indicating the loss of LDA was due to loss of titin as a length sensor. Interestingly, immunofluorescence showed that GSK-3β localized to the z-disc when phosphorylated at Y216 and, via mass spectrometry, phosphorylated primarily z-disc proteins including several sites on the structural protein Ablim-1, which we showed also localizes to the z-disc. These data suggested that GSK-3β’s effect on titin is likely through altering its ability to anchor to the z-disc through targeting of these z-disc proteins. To provide further evidence that GSK-3β is specifically altering LDA, we genetically removed a downstream effecter of LDA, cardiac myosin binding protein-C (cMyBP-C). In vitro treatment with exogenous GSK-3β was able to increase calcium sensitivity at long SLs in both KO and WT mice but had no effect on cMyBPC KO mice or mice lacking the c-terminal domains of cMyBPC that are known to be important for LDA. Lastly, we found that human heart failure patients had less myofilament GSK-3β compared to non-failing patients, and that these same samples had a depressed LDA. This work has identified a novel mechanism by which GSK-3β localizes to the myofilament to modulate LDA and indicates that z-disc localized GSK-3β may be a possible therapeutic target to restore the Frank-Starling mechanism in heart failure patients.

МЕТОДЫ ФИКСАЦИИ КОСТНЫХ ОТЛОМКОВ ПРИ ПЕРЕЛОМАХ НИЖНЕЙ ЧЕЛЮСТИ

Thing. A review of the literature devoted to the topical problem of maxillofacial surgery and surgical dentistry – methods of treating patients with mandibular fractures was carried out.&#x0D; The aim of the study is to review the materials of publications on the methods of treatment of patients with mandibular fractures.&#x0D; Methodology. The publications of domestic and foreign authors, considering methods of fixation of bone fragments in lower jaw fractures, have been studied.&#x0D; Results. Publications indicate that there are many treatments for mandibular fractures. Research results demonstrate the importance of bone stabilization for bone fusion. A common disadvantage of conservative and surgical methods of treatment is unstable fixation of bone fragments, which is the most common cause of delayed consolidation of a mandibular fracture. The presented studies show that bone osteosynthesis with metal plates is considered the most appropriate method for treating mandibular fractures.&#x0D; Conclusions. Splinting as a method of treating fractures of the lower jaw has a large number of disadvantages. A common disadvantage of methods for splinting the lower jaw is that these structures do not always provide anatomical reduction and stability for the entire period of consolidation or require mandatory intermaxillary fixation, the lower jaw is fixed in the central occlusion position, which is not a position of physiological rest, and leads to passive muscle tension. depriving them of active function.&#x0D; The main disadvantage of the methods of osteosynthesis using a suture and using wires is that it is difficult to achieve stable fixation of fragments using these techniques.&#x0D; Combined methods of fixation of bone fragments (use of a bone suture and dental splints) provide a stronger fixation of the fragments.&#x0D; In the past two decades, in the treatment of mandibular fractures, there has been an increase in the trend towards rigid or semi-rigid osteosynthesis using plates.&#x0D; The disadvantages of compression osteosynthesis is that significant compression can lead to ischemia and slow down the formation of callus.&#x0D; A common disadvantage of conservative and surgical methods of treatment is unstable fixation of bone fragments, which is the most common reason for their delayed consolidation.&#x0D; Bone osteosynthesis with metal plates is considered a more progressive method of treating mandibular fractures.

Long-Term PDE-5A Inhibition Improves Myofilament Function in Left and Right Ventricular Cardiomyocytes through Partially Different Mechanisms in Diabetic Rat Hearts.

Heart failure with preserved ejection fraction (HFpEF) and right ventricular (RV) dysfunction are frequent complications of diabetic cardiomyopathy. Here we aimed to characterize RV and left ventricular (LV) remodeling and its prevention by vardenafil (a long-acting phosphodiesterase-5A (PDE-5A) inhibitor) administration in a diabetic HFpEF model. Zucker Diabetic Fatty (ZDF) and control, ZDF Lean (Lean) male rats received 10 mg/kg vardenafil (ZDF + Vard; Lean + Vard) per os, on a daily basis for a period of 25 weeks. In vitro force measurements, biochemical and histochemical assays were employed to assess cardiomyocyte function and signaling. Vardenafil treatment increased cyclic guanosine monophosphate (cGMP) levels and decreased 3-nitrotyrosine (3-NT) levels in the left and right ventricles of ZDF animals, but not in Lean animals. Cardiomyocyte passive tension (Fpassive) was higher in LV and RV cardiomyocytes of ZDF rats than in those receiving preventive vardenafil treatment. Levels of overall titin phosphorylation did not differ in the four experimental groups. Maximal Ca2+-activated force (Fmax) of LV and RV cardiomyocytes were preserved in ZDF animals. Ca2+-sensitivity of isometric force production (pCa50) was significantly higher in LV (but not in RV) cardiomyocytes of ZDF rats than in their counterparts in the Lean or Lean + Vard groups. In accordance, the phosphorylation levels of cardiac troponin I (cTnI) and myosin binding protein-C (cMyBP-C) were lower in LV (but not in RV) cardiomyocytes of ZDF animals than in their counterparts of the Lean or Lean + Vard groups. Vardenafil treatment normalized pCa50 values in LV cardiomyocytes, and it decreased pCa50 below control levels in RV cardiomyocytes in the ZDF + Vard group. Our data illustrate partially overlapping myofilament protein alterations for LV and RV cardiomyocytes in diabetic rat hearts upon long-term PDE-5A inhibition. While uniform patterns in cGMP, 3-NT and Fpassive levels predict identical effects of vardenafil therapy for the diastolic function in both ventricles, the uneven cTnI, cMyBP-C phosphorylation levels and pCa50 values implicate different responses for the systolic function.

Elasticity of baseball players’ posterior shoulder capsule during internal rotation stretching at 30 degrees of scaption

Previous cadaveric studies have identified effective stretching positions for the posterior shoulder capsules; however, it is unknown whether these stretching positions are also effective in overhead athletes. This study aimed to investigate whether passive tension was generated in the posterior shoulder capsules in baseball players during stretching positions identified in previous cadaveric studies. Fifteen male baseball players without prior shoulder injuries or surgeries participated in this study. We measured the shear moduli of the middle and inferior posterior capsules of the dominant shoulder in the resting (neutral shoulder internal/external rotation at 30 degrees of flexion) and stretching (maximal shoulder internal rotation at 30 degrees of scapular plane elevation (scaption)) positions using ultrasound shear wave elastography. The shear moduli of the middle posterior capsule were significantly higher in the stretching position than in the resting position (resting vs stretching: 20.9 vs 34.6 kPa, P < .001); however, there was no significant difference in the shear moduli between both positions in the inferior posterior capsule (22.3 vs 29.5 kPa, P = .120). Our results revealed that a large amount of passive tension is generated in the middle posterior capsule during shoulder internal rotation stretching at 30 degrees of scaption in overhead athletes.

Extracellular vesicles derived from physiologically loaded living myocardial slices improve the contractility of healthy living myocardial slices

Abstract Introduction Mechanical load is a determinant of the healthy-to-failing myocardium transition. Extracellular vesicles (EVs) found in the range of 30–200 nm contain bioactive cargoes such as DNA, miRNA and proteins, and thus are considered important mediators of the paracrine crosstalk between cells in health and disease. Living myocardial slices (LMS) are 300μm layers of myocardial tissue that allow modelling of the intercellular communication in the heart. Purpose To assess whether secretion of EVs derived from physiological or pathological mechanically-loaded LMS regulate changes in myocardial contractility. Methods LMS were prepared from adult male Sprague-Dawley rats' left ventricle using a vibratome. LMS were stretched uniaxially using customised stretchers at a sarcomere length of 2.2μm and 2.4μm to recapitulate a physiological (P) and an overload (O) condition, respectively. LMS were cultured for 48-hours under electromechanical stimulation in M-199 media with Earls' salts, catecholamines, dexamethasone and triiodothyronine. After culture, media was harvested and processed for exosomes isolation by size exclusion chromatography. Particle size and concentration was assessed by nanoparticle tracking analysis. To validate the different phenotypes in LMS, force-stretch relationship was assessed after 48-hours culture. EVs isolated from P and O LMS were then used to treat physiologically loaded LMS (1x107 particles/LMS) and the force-stretch relationship was assessed after 48-hours culture. Results No significant difference in contractility was found between P and O LMS at any stretch increment (5.99±1.10 vs 2.82±0.92 mN/mm2 max force), whilst a significant increase in the passive tension of myocardial tissue was observed at 25% (15.90±2.77 vs 4.67±0.37 mN/mm2; p&amp;lt;0.05,) and 30% stretch (21.92±3.60 vs 5.73±0.6 mN/mm2; p&amp;lt;0.001) in the P LMS compared to O LMS (n=11 P, n=4 O). EVs quantification showed no significant difference between P and O conditions (1.16329E+11±4587386608 vs 1.08915E+11±7641744894 particles/ml); (n=7 P; n=3 O). However, P EVs-treated LMS showed a significant increase in contractility after 48-hours, compared to PBS-treated LMS at 25% (8.49±0.62 vs 5.34±0.9 mN/mm2) and 30% stretch (9.55±0.42 vs 5.99±1.10 mN/mm2; p&amp;lt;0.05); (n=11 PBS, n=4 P EVs,) and O EVs-treated LMS from 15–30% stretch (9.55±0.42 vs 3.23±0.55 mN/mm2 max force; p&amp;lt;0.0001); (n=4 P EVs, n=5 O EVs). Conversely, no significant differences in contractility were found between PBS-treated LMS and O EVs-treated LMS (5.99±1.10 vs 3.23±0.55 mN/mm2 maximum force); (n=5 O EVs, n=11 PBS). Conclusions EVs derived from physiologically loaded LMS improve the contractility of healthy LMS after 48-hours culture compared to PBS-treated LMS. Understanding how mechanical load correlates with specific loading of cargoes in EVs may reveal interesting therapeutic targets for the treatment of heart failure. Funding Acknowledgement Type of funding sources: Private grant(s) and/or Sponsorship. Main funding source(s): British Heart Foundation Physiological and overloaded phenotypesContractility of EVs treated LMS

NOS-dependent effects of plantar mechanical stimulation on mechanical characteristics and cytoskeletal proteins in rat soleus muscle during hindlimb suspension.

The study was aimed at investigating the mechanisms and structures which determine mechanical properties of skeletal muscles under gravitational unloading and plantar mechanical stimulation (PMS). We hypothesized that PMS would increase NO production and prevent an unloading-induced reduction in skeletal muscle passive stiffness. Wistar rats were hindlimb suspended and subjected to a daily PMS and one group of stimulated animals was also treated with nitric oxide synthase (NOS) inhibitor (L-NAME). Animals received mechanical stimulation of the feet for 4h a day throughout 7-day hindlimb suspension (HS) according to a scheme that mimics the normal walking of the animal. Seven-day HS led to a significant reduction in soleus muscle weight by 25%. However, PMS did not prevent the atrophic effect induced by HS. Gravitational unloading led to a significant decrease in maximum isometric force and passive stiffness by 38% and 31%, respectively. The use of PMS prevented a decrease in the maximum isometric strength of the soleus muscle. At the same time, the passive stiffness of the soleus in the PMS group significantly exceeded the control values by 40%. L-NAME (NOS inhibitor) administration attenuated the effect of PMS on passive stiffness and maximum force of the soleus muscle. The content of the studied cytoskeletal proteins (α-actinin-2, α-actinin-3, desmin, titin, nebulin) decreased after 7-day HS, but this decrease was successfully prevented by PMS in a NOS-dependent manner. We also observed significant decreases in mRNA expression levels of α-actinin-2, desmin, and titin after HS, which was prevented by PMS. The study also revealed a significant NOS-dependent effect of PMS on the content of collagen-1a, but not collagen-3a. Thus, PMS during mechanical unloading is able to maintain soleus muscle passive tension and force as well as mRNA transcription and protein contents of cytoskeletal proteins in a NOS-dependent manner.

Impact of chronic obstructive pulmonary disease on passive viscoelastic components of the musculoarticular system

Chronic obstructive pulmonary disease (COPD) produces skeletal muscle atrophy and weakness, leading to impairments of exercise performance. The mechanical work needed for movement execution is also provided by the passive tension developed by musculoarticular connective tissue. To verify whether COPD affects this component, the passive viscoelastic properties of the knee joint were evaluated in 11 patients with COPD and in 11 healthy individuals. The levels of stiffness and viscosity were assessed by means of the pendulum test, consisting in a series of passive leg oscillations. In addition, to explore the contribution of passive tension in the mechanical output of a simple motor task, voluntary leg flexion–extension movements were performed. Patients with COPD showed a statistically significant reduction in stiffness and viscosity compared to controls. Voluntary execution of flexion–extension movements revealed that the electromyographic activity of the Rectus Femoris and Biceps Femoris was lower in patients than in controls, and the low viscoelastic tension in the patients conditioned the performance of active movements. These results provide novel insights on the mechanism responsible for the movement impairments associated with COPD.