Normal Muscle Function Research Articles

Protein kinase 2 of the giant sarcomeric protein UNC-89 regulates mitochondrial morphology and function

UNC-89 is a giant sarcomeric M-line protein required for sarcomere organization and optimal muscle function. UNC-89 contains two protein kinase domains, PK1 and PK2, separated by an elastic region. Here we show that PK2 is a canonical kinase expected to be catalytically active. C. elegans expressing UNC-89 with a lysine to alanine (KtoA) mutation to inactivate PK2 have normally organized sarcomeres and SR, and normal muscle function. PK2 KtoA mutants have fragmented mitochondria, correlated with more mitochondrially-associated DRP-1. PK2 KtoA mutants have increased ATP levels, increased glycolysis and altered levels of electron transport chain complexes. Muscle mitochondria show increased complex I and decreased complex II basal respiration, each of which cannot be uncoupled. This suggests that mutant mitochondria are already uncoupled, possibly resulting from an increased level of the uncoupling protein, UCP-4. Our results suggest signaling from sarcomeres to mitochondria, to help match energy requirements with energy production.

Leiomodin 2 neonatal dilated cardiomyopathy mutation results in altered actin gene signatures and cardiomyocyte dysfunction

Neonatal dilated cardiomyopathy (DCM) is a poorly understood muscular disease of the heart. Several homozygous biallelic variants in LMOD2, the gene encoding the actin-binding protein Leiomodin 2, have been identified to result in severe DCM. Collectively, LMOD2-related cardiomyopathies present with cardiac dilation and decreased heart contractility, often resulting in neonatal death. Thus, it is evident that Lmod2 is essential to normal human cardiac muscle function. This study aimed to understand the underlying pathophysiology and signaling pathways related to the first reported LMOD2 variant (c.1193 G > A, p.Trp398*). Using patient-specific human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) and a mouse model harboring the homologous mutation to the patient, we discovered dysregulated actin-thin filament lengths, altered contractility and calcium handling properties, as well as alterations in the serum response factor (SRF)-dependent signaling pathway. These findings reveal that LMOD2 may be regulating SRF activity in an actin-dependent manner and provide a potential new strategy for the development of biologically active molecules to target LMOD2-related cardiomyopathies.

The Double-Edged Sword of ROS in Muscle Wasting and COPD: Insights from Aging-Related Sarcopenia.

An elevation in reactive oxygen species (ROS) is widely accepted to be a key mechanism that drives chronic obstructive pulmonary disease (COPD) and its major co-morbidity, skeletal muscle wasting. However, it will be perhaps a surprise to many that an elevation in ROS in skeletal muscle is also a critical process for normal skeletal muscle function and in the adaptations to physical exercise. The key message here is that ROS are not solely detrimental. This duality of ROS suggests that the mere use of a broad-acting antioxidant is destined to fail in alleviating skeletal muscle wasting in COPD because it will also be influencing critical physiological ROS-dependent processes. Here, we take a close look at this duality of ROS in skeletal muscle physiology and pathophysiology pertaining to COPD and will aim to gain critical insights from other skeletal muscle wasting conditions due to aging such as sarcopenia.

The Role of Branched Chain Ketoacid Dehydrogenase Kinase (BCKDK) in Skeletal Muscle Biology and Pathogenesis.

Muscle wasting can be caused by nutrition deficiency and inefficient metabolism of amino acids, including Branched Chain Amino Acids (BCAAs). Branched Chain Amino Acids are a major contributor to the metabolic needs of healthy muscle and account for over a tenth of lean muscle mass. Branched chain alpha-ketoacid dehydrogenase (BCKD) is the rate limiting enzyme of BCAA metabolism. Inhibition of BCKD is achieved through a reversible phosphorylation event by Branched Chain a-ketoacid dehydrogenase kinase (BCKDK). Our study set out to determine the importance of BCKDK in the maintenance of skeletal muscle. We used the Gene Expression Omnibus Database to understand the role of BCKDK in skeletal muscle pathogenesis, including aging, muscular disease, and interrupted muscle metabolism. We found BCKDK expression levels were consistently decreased in pathologic conditions. These results were most consistent when exploring muscular disease followed by aging. Based on our findings, we hypothesize that decreased BCKDK expression alters BCAA catabolism and impacts loss of normal muscle integrity and function. Further research could offer valuable insights into potential therapeutic strategies for addressing muscle-related disorders.

Fueling the heartbeat: Dynamic regulation of intracellular ATP during excitation–contraction coupling in ventricular myocytes

The heart beats approximately 100,000 times per day in humans, imposing substantial energetic demands on cardiac muscle. Adenosine triphosphate (ATP) is an essential energy source for normal function of cardiac muscle during each beat, as it powers ion transport, intracellular Ca2+ handling, and actin-myosin cross-bridge cycling. Despite this, the impact of excitation-contraction coupling on the intracellular ATP concentration ([ATP]i) in myocytes is poorly understood. Here, we conducted real-time measurements of [ATP]i in ventricular myocytes using a genetically encoded ATP fluorescent reporter. Our data reveal rapid beat-to-beat variations in [ATP]i. Notably, diastolic [ATP]i was <1 mM, which is eightfold to 10-fold lower than previously estimated. Accordingly, ATP-sensitive K+ (KATP) channels were active at physiological [ATP]i. Cells exhibited two distinct types of ATP fluctuations during an action potential: net increases (Mode 1) or decreases (Mode 2) in [ATP]i. Mode 1 [ATP]i increases necessitated Ca2+ entry and release from the sarcoplasmic reticulum (SR) and were associated with increases in mitochondrial Ca2+. By contrast, decreases in mitochondrial Ca2+ accompanied Mode 2 [ATP]i decreases. Down-regulation of the protein mitofusin 2 reduced the magnitude of [ATP]i fluctuations, indicating that SR-mitochondrial coupling plays a crucial role in the dynamic control of ATP levels. Activation of β-adrenergic receptors decreased [ATP]i, underscoring the energetic impact of this signaling pathway. Finally, our work suggests that cross-bridge cycling is the largest consumer of ATP in a ventricular myocyte during an action potential. These findings provide insights into the energetic demands of EC coupling and highlight the dynamic nature of ATP concentrations in cardiac muscle.

Physiological role for S-nitrosylation of RyR1 in skeletal muscle function and development

Excitation-contraction coupling in skeletal muscle myofibers depends upon Ca2+ release from the sarcoplasmic reticulum through the ryanodine receptor/Ca2+-release channel RyR1. The RyR1 contains ∼100 Cys thiols of which ∼30 comprise an allosteric network subject to posttranslational modification by S-nitrosylation, S-palmitoylation and S-oxidation. However, the role and function of these modifications is not understood. Although aberrant S-nitrosylation of multiple unidentified sites has been associated with dystrophic diseases, malignant hyperthermia and other myopathic syndromes, S-nitrosylation in physiological situations is reportedly specific to a single (1 of ∼100) Cys in RyR1, Cys3636 in a manner gated by pO2. Using mice expressing a form of RyR1 with a Cys3636→Ala point mutation to prevent S-nitrosylation at this site, we showed that Cys3636 was the principal target of endogenous S-nitrosylation during normal muscle function. The absence of Cys3636 S-nitrosylation suppressed stimulus-evoked Ca2+ release at physiological pO2 (at least in part by altering the regulation of RyR1 by Ca2+/calmodulin), eliminated pO2 coupling, and diminished skeletal myocyte contractility in vitro and measures of muscle strength in vivo. Furthermore, we found that abrogation of Cys3636 S-nitrosylation resulted in a developmental defect reflected in diminished myofiber diameter, altered fiber subtypes, and altered expression of genes implicated in muscle development and atrophy. Thus, our findings establish a physiological role for pO2-coupled S-nitrosylation of RyR1 in skeletal muscle contractility and development and provide foundation for future studies of RyR1 modifications in physiology and disease.

The effect of suboccipital muscle dysfunction on the biomechanics of the upper cervical spine: a study based on finite element analysis

ObjectiveMuscle dysfunction caused by repetitive work or strain in the neck region can interfere muscle responses. Muscle dysfunction can be an important factor in causing cervical spondylosis. However, there has been no research on how the biomechanical properties of the upper cervical spine change when the suboccipital muscle group experiences dysfunction. The objective of this study was to investigate the biomechanical evidence for cervical spondylosis by utilizing the finite element (FE) approach, thus and to provide guidance for clinicians performing acupoint therapy.MethodsBy varying the elastic modulus of the suboccipital muscle, the four FE models of C0-C3 motion segments were reconstructed under the conditions of normal muscle function and muscle dysfunction. For the two normal condition FE models, the elastic modulus for suboccipital muscles on both sides of the C0-C3 motion segments was equal and within the normal range In one muscle dysfunction FE model, the elastic modulus on both sides was equal and greater than 37 kPa, which represented muscle hypertonia; in the other, the elastic modulus of the left and right suboccipital muscles was different, indicating muscle imbalance. The biomechanical behavior of the lateral atlantoaxial joint (LAAJ), atlanto-odontoid joint (ADJ), and intervertebral disc (IVD) was analyzed by simulations, which were carried out under the six loadings of flexion, extension, left and right lateral bending, left and right axial rotation.ResultsUnder flexion, the maximum stress in LAAJ with muscle imbalance was higher than that with normal muscle and hypertonia, while the maximum stress in IVD in the hypertonic model was higher than that in the normal and imbalance models. The maximum stress in ADJ was the largest under extension among all loadings for all models. Muscle imbalance and hypertonia did not cause overstress and stress distribution abnormalities in ADJ.ConclusionMuscle dysfunction increases the stress in LAAJ and in IVD, but it does not affect ADJ.

Normal Skeletal Muscle Growth and Function Require Insulin Receptors Expressed by Cholinergic Motor Neurons

It is well known that insulin stimulates skeletal muscle growth. However, it is currently unknown how insulin does so since it was previously shown that insulin receptors expressed by skeletal muscles are dispensable in this regard. In this study, we focused on insulin receptors expressed by the cholinergic motor neurons and generated conditional knockout mice which lack insulin receptors specifically in the cholinergic neurons. We found that insulin activates cholinergic motor neurons and that insulin receptors expressed by the cholinergic neurons are required for normal growth of skeletal muscle. We also noted that the conditional knockout mice have underdeveloped neuromuscular junction and compromised skeletal muscle function. Together, our study suggests that insulin stimulates and activates cholinergic motor neurons to promote normal skeletal muscle growth and function. This work was supported by the National Research Foundation of Korea (NRF-2022R1A2C3005613 to Jong-Woo Sohn) funded by the Korean Ministry of Science and ICT. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Compatibility of eugenol anesthesia with classroom physiology experiments on nerve and muscle of frogs

Frogs serve as valuable model organisms for studying physiological responses of nerve, skeletal muscle and the heart in undergraduate biology labs. Heretofore, induced hypothermia has been the preferred technique for pain and stress reduction prior to euthanasia by pithing. However, AVMA guidelines discourage hypothermia for restraint or euthanasia of amphibians and advocate anesthetic overdose as preferable to pithing alone. Unfortunately, the primary anesthetic used in fish and other aquatic invertebrates, MS-222, blocks normal nerve and muscle function in leopard frogs and renders them useless for classroom physiology experiments, as demonstrated by Medler (2019). Eugenol is a safe and affordable anesthetic that is effective in amphibians. We sought to test the hypothesis that eugenol anesthesia is compatible with classroom nerve and muscle experiments on frogs. Bullfrogs and leopard frogs were immersed in a bath of eugenol suspended in tap water at 275 to 350 mg/L. At various time points, a four step reflex test was performed including tests of righting response, superficial pain reflex, deep pain reflex, and corneal blink reflex. Once all reflexes were absent, the frog was euthanized by pithing and the gastrocnemius muscle was prepared for force recordings. The sciatic nerve was stimulated with a bipolar stimulating electrode while gastrocnemius force was measured using an isometric force transducer. The threshold voltage eliciting a muscle contraction and the peak isometric twitch force were recorded at 15 minute intervals for 2 hours. Control frogs were sedated by immersion in ice water for 20 to 30 minutes, pithed when reflexes were substantially weakened, and then subjected to the same stimulation protocol and force measurements. At these doses, eugenol reliably induces loss of reflexes in 20 to 35 minutes and neuromuscular preparations maintain the ability to respond to electrical stimulation. Preliminary results suggest that eugenol may produce a modest elevation of threshold voltage and a modest reduction in maximum twitch force compared to control frogs euthanized without chemical anesthesia. Eugenol may be an effective anesthetic to prepare bullfrogs and leopard frogs for classroom experiments on nerve and muscle. Funding was provided by the Bill and Linda Frost Fund. This is the full abstract presented at the American Physiology Summit 2024 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.

Mustn1 is a smooth muscle cell-secreted microprotein that modulates skeletal muscle extracellular matrix composition

ObjectiveSkeletal muscle plasticity and remodeling are critical for adapting tissue function to use, disuse, and regeneration. The aim of this study was to identify genes and molecular pathways that regulate the transition from atrophy to compensatory hypertrophy or recovery from injury. Here, we have used a mouse model of hindlimb unloading and reloading, which causes skeletal muscle atrophy, and compensatory regeneration and hypertrophy, respectively. MethodsWe analyzed mouse skeletal muscle at the transition from hindlimb unloading to reloading for changes in transcriptome and extracellular fluid proteome. We then used qRT-PCR, immunohistochemistry, and bulk and single-cell RNA sequencing data to determine Mustn1 gene and protein expression, including changes in gene expression in mouse and human skeletal muscle with different challenges such as exercise and muscle injury. We generated Mustn1-deficient genetic mouse models and characterized them in vivo and ex vivo with regard to muscle function and whole-body metabolism. We isolated smooth muscle cells and functionally characterized them, and performed transcriptomics and proteomics analysis of skeletal muscle and aorta of Mustn1-deficient mice. ResultsWe show that Mustn1 (Musculoskeletal embryonic nuclear protein 1, also known as Mustang) is highly expressed in skeletal muscle during the early stages of hindlimb reloading. Mustn1 expression is transiently elevated in mouse and human skeletal muscle in response to intense exercise, resistance exercise, or injury. We find that Mustn1 expression is highest in smooth muscle-rich tissues, followed by skeletal muscle fibers. Muscle from heterozygous Mustn1-deficient mice exhibit differences in gene expression related to extracellular matrix and cell adhesion, compared to wild-type littermates. Mustn1-deficient mice have normal muscle and aorta function and whole-body glucose metabolism. We show that Mustn1 is secreted from smooth muscle cells, and that it is present in arterioles of the muscle microvasculature and in muscle extracellular fluid, particularly during the hindlimb reloading phase. Proteomics analysis of muscle from Mustn1-deficient mice confirms differences in extracellular matrix composition, and female mice display higher collagen content after chemically induced muscle injury compared to wild-type littermates. ConclusionsWe show that, in addition to its previously reported intracellular localization, Mustn1 is a microprotein secreted from smooth muscle cells into the muscle extracellular space. We explore its role in muscle ECM deposition and remodeling in homeostasis and upon muscle injury. The role of Mustn1 in fibrosis and immune infiltration upon muscle injury and dystrophies remains to be investigated, as does its potential for therapeutic interventions.

Abstract 13310: TTN Variants and Arrhythmic Risk Among Countywide Sudden Deaths: From the San Francisco Postmortem Systematic Investigation of Sudden Cardiac Death Study

Background: Titin, encoded by TTN , is a sarcomeric protein necessary for normal cardiac and skeletal muscle function. Truncating variants in the A-band are a frequent cause of isolated and familial dilated cardiomyopathy (DCM) in living cohorts. Whether variants outside of the A-band confer arrhythmic risk remains unclear. We investigated the yield and distribution of TTN variants in a postmortem study of presumed sudden cardiac deaths (pSCDs) in San Francisco County. Methods: From 2/1/2011 to 12/31/2017, the Postmortem Systematic Investigation of Sudden Cardiac Death study performed complete autopsies on 889 incident deaths (age 16-90) meeting World Health Organization criteria for SCD (pSCD). Using clinical records, autopsy findings, and family history, we performed deep phenotyping to adjudicate underlying arrhythmic “SAD” (potentially rescuable with defibrillation) or non-arrhythmic “non-SAD” (tamponade, overdose, etc.) cause of pSCD. We performed clinical whole exome testing on cases with next of kin consent. Results: Of the 322 pSCDs tested (196 SAD, 126 non-SAD), we detected 5 truncating/splice variants located in non-A-band regions (p=0.03 vs. none found in the A-band) in 4 cases, all SAD. No truncating/splice variants were detected in 47 cases with autopsy evidence of DCM (cardiomegaly and short axis &gt; 3.5cm). Overall, 89 cases had at least 1 TTN variant of uncertain significance (VUS): 61 (68.5%) SADs and 28 (31.5%) non-SADs, with a trend towards more TTN VUSs among SADs (p =0.10). A total of 110 VUSs were found: 10 (9.1%) in the Z-disc, 38 (34.5%) in the I-band, 50 (45.5%) in the A-band, and 12 (10.9%) in the M-band. TTN VUSs clustered similarly throughout the gene in SADs and non-SADs. Conclusion: In this 7-year postmortem genetic study of unselected countywide sudden deaths using autopsy to adjudicate arrhythmic cause, we found TTN truncating/splice variants in non-A-band regions were associated with SAD and a trend toward association with SAD among TTN VUS carriers. In contrast to living cohorts with diagnosed DCM, no cases meeting autopsy criteria for DCM had a truncating/splice variant. Since non-survivors (i.e., SCDs) are underrepresented in DCM cohorts, our results suggest a potential role for non-A band TTN variants in arrhythmic risk.

Effects of Aging on Collagen in the Skeletal Muscle of Mice.

Aging affects several tissues in the body, including skeletal muscle. Multiple types of collagens are localized in the skeletal muscle and contribute to the maintenance of normal muscle structure and function. Since the effects of aging on muscle fibers vary by muscle fiber type, it is expected that the effects of aging on intramuscular collagen might be influenced by muscle fiber type. In this study, we examined the effect of aging on collagen levels in the soleus (slow-twitch muscle) and gastrocnemius (fast-twitch muscle) muscles of 3-, 10-, 24-, and 28-month-old male C57BL/6J mice using molecular and morphological analysis. It was found that aging increased collagen I, III, and VI gene expression and immunoreactivity in both slow- and fast-twitch muscles and collagen IV expression in slow-twitch muscles. However, collagen IV gene expression and immunoreactivity in fast-twitch muscle were unaffected by aging. In contrast, the expression of the collagen synthesis marker heat shock protein 47 in both slow- and fast-twitch muscles decreased with aging, while the expression of collagen degradation markers increased with aging. Overall, these results suggest that collagen gene expression and immunoreactivity are influenced by muscle fiber type and collagen type and that the balance between collagen synthesis and degradation tends to tilt toward degradation with aging.

Association of sarcopenia, pre-sarcopenia, and dynapenia with the onset and progression of locomotive syndrome in Japanese older adults: a cross-sectional study

BackgroundSarcopenia commonly occurs in older adults with motor disorders requiring long-term care, and the clinical features of sarcopenia are associated with locomotive syndrome. Dynapenia is the age-related loss of muscle strength. However, the association of sarcopenia and dynapenia with the onset and progression of locomotive syndrome in older adults remains unknown. The current study aimed to determine the association of sarcopenia, pre-sarcopenia, and dynapenia with the onset and progression of locomotive syndrome in Japanese older adults.MethodsThis study included older females (n = 264, 73.9 ± 5.8 years) and males (n = 92, 76.3 ± 6.1 years). Sarcopenia was defined as low muscle function and mass; pre-sarcopenia was defined as low muscle mass with normal muscle function; and dynapenia was defined as low muscle function without low muscle mass. Locomotive syndrome (stage 0–2) severity was determined using the stand-up test, the two-step test, and the 25-question geriatric locomotive function scale. Logistic regression analysis was performed to determine the relationship between sarcopenia category and locomotive syndrome stages.ResultsAge (1.208, 95% confidence interval (CI) 1.124–1.298), sex (2.455, 95% CI 1.241–4.856), and BMI (1.211, 95% CI 1.077–1.361) were significant variables for determining locomotive syndrome stage ≥ 1, whereas pre-sarcopenia (0.543, 95% CI 0.331–0.891) and sarcopenia (1.664, 95% CI 1.005–2.755) were significant variables for determining locomotive syndrome stage 2.ConclusionsOnly sarcopenia was associated with locomotive syndrome progression, while low muscle mass or low muscle function was not associated with locomotive syndrome. Gaining muscle mass accompanied by an increased muscle function for older adults is warranted to prevent locomotive syndrome progression in the super-aged society.

Post-operative pulmonary complications after thoracic and upper abdominal procedures at referral hospitals in Amhara region, Ethiopia: a multi-center study.

Thoraco-abdominal surgery cuts through muscle, disrupting the normal structure and function of the respiratory muscles, resulting in lower lung volumes and a higher risk of developing post-operative pulmonary complications (PPC). PPC remains an important cause of post-operative morbidity and mortality and impacts the long-term outcomes of patients after hospital discharge. This study was aimed at determining the incidence and factors associated with postoperative pulmonary complications among patients who underwent thoracic and upper abdominal surgery in the Amhara region of Ethiopia. A multi-center follow-up study was conducted from April 1, 2022, to June 30, 2022, at comprehensive specialized hospitals in Amhara regional state, northwest Ethiopia. 424 patients were consecutively included in this study, with a response rate of 100%. A chart review and patient interview were used to collect data. A logistic regression analysis was performed to assess the strength of the association of independent variables with postoperative pulmonary complications.The crude odds ratio (COR) and adjusted odds ratio (AOR) with the corresponding 95% confidence interval were computed. Variables with a p-value of <0.05 were considered statistically significant predictors of the outcome variable. The incidence of postoperative pulmonary complication was 24.5%. Emergency procedures, preoperative SpO2 < 94%, duration of surgery >2 h, patients with a nasogastric tube, intraoperative blood loss >500 ml and post-operative albumin <3.5 g/dl were factors associated with pulmonary complications. The most common complications were pneumonia (9.9%) followed by respiratory infection (4.2%). The incidence of postoperative pulmonary complication after thoracic and upper abdominal surgery remains high. Preoperative SpO2, duration of surgery, patients having a nasogastric tube, intraoperative blood loss and post-operative albumin were factors associated with post-operative pulmonary complications.

Lack of adipocyte IP3R1 reduces diet-induced obesity and greatly improves whole-body glucose homeostasis

The normal function of skeletal muscle and adipose tissue ensures whole-body glucose homeostasis. Ca2+ release channel inositol 1,4,5-trisphosphate receptor 1 (IP3R1) plays a vital role in regulating diet-induced obesity and disorders, but its functions in peripheral tissue regulating glucose homeostasis remain unexplored. In this study, mice with Ip3r1 specific knockout in skeletal muscle or adipocytes were used for investigating the mediatory role of IP3R1 on whole-body glucose homeostasis under normal or high-fat diet. We reported that IP3R1 expression levels were increased in the white adipose tissue and skeletal muscle of diet-induced obese mice. Ip3r1 knockout in skeletal muscle improved glucose tolerance and insulin sensitivity of mice on a normal chow diet, but worsened insulin resistance in diet-induced obese mice. These changes were associated with the reduced muscle weight and compromised Akt signaling activation. Importantly, Ip3r1 deletion in adipocytes protected mice from diet-induced obesity and glucose intolerance, mainly due to the enhanced lipolysis and AMPK signaling pathway in the visceral fat. In conclusion, our study demonstrates that IP3R1 in skeletal muscle and adipocytes exerts divergent effects on systemic glucose homeostasis, and characterizes adipocyte IP3R1 as a promising target for treating obesity and type 2 diabetes.

Study of 60 Adult Patients to Compare Standard Postoperative Clinical Assessment with Train-of-Four Ratio ≥0.9 on Patient Outcomes Using Postoperative Spirometry and Neuromuscular Function Measurements Following Extubation

BACKGROUND Postoperative tracheal extubation requires optimal timing to ensure patient safety and normal muscle function. The train-of-four ratio (TOFR) of the fourth muscle response compared with the first indicates a non-depolarizing neuromuscular block, and a ratio ≥0.9 can be used as an objective measurement of neuromuscular reversal. This study of 60 adult patients who underwent elective surgery with general anesthesia that included the neuromuscular blocking agent cisatracurium aimed to compare standard postoperative clinical assessment with the TOFR ≥0.9 on patient outcomes using postoperative neuromuscular function assessed by grip strength and ability to sit up unaided and spirometry measurements following extubation. MATERIAL AND METHODS The 30 patients extubated postoperatively in the TOF group were required to have a TOFR ≥0.9, while the 30 patients in the clinical assessment group were awake and following simple commands and had a 5-second head lift and spontaneous breathing with acceptable oxygenation. The main outcomes were the incentive spirometry and grip strength and ability to sit up unaided measured at 10, 30, 50 min and 24 h after extubation. RESULTS The groups had no difference in recovery path of incentive spirometry volume (P=0.072) and no difference in postoperative incentive spirometry decrease from baseline except at 10 min after extubation (P=0.005). There was no difference in handgrip strength and independent sitting between groups. CONCLUSIONS The findings showed that using the TOF ratio ≥0.9 before extubation did not improve early postoperative strength quantified by spirometry volume, handgrip strength, and proportion of unaided sitting.

Glu-rich N-terminal variable region of troponin T functions as a myofilament Ca2+-reservoir to reduce SR Ca2+-cycling.

The long Glu-rich N-terminal segment of avian pectoral muscle troponin T (TnT) and C-terminal extension of insect TnT are multi-valent Ca2+-binding sites with physiologically relevant affinities. Genetic deletion of the Glu-rich C-terminal extension of insect TnT decreases muscle and heart functions but increases the tolerance of cardiomyocytes to Ca2+ overloading, indicating decreased [Ca2+]i. In contrast, cardiomyocytes from gene-edited mice expressing modified cardiac TnT with N-terminal variable region replaced by a C-terminal segment of insect TnT (51E-cTnT) show higher shortening amplitude and contraction and relaxation velocities than that of wild type (WT) control. Isolated 51E-cTnT cardiomyocytes exhibited shorter resting sarcomeres, which can be corrected by inhibiting myosin ATPase, indicating increased resting [Ca2+]i. A similar gain-of-function model,fast skeletal muscle TnTgene-edited mice with the N-terminal variable region replaced by the N-terminal segment of adult turkey pectoral muscle TnT (Tx9-fsTnT), shows normal baseline muscle functions but slower and less rising of contractile force during caffeine-induced Ca2+ release from sarcoplasmic reticulum (SR) than that of WT control, indicating a decreased SR Ca2+ store. Consistently, 51E-cTnT mouse hearts respond to beta-adrenergic stimulation or Ca2+ agonist with higher than WT ventricular peak pressure and diastolic velocity. The data support a hypothesis that the Glu-rich segments of insect and avian flight muscle TnT function as myofilament Ca2+ reservoirs to tune muscle kinetics and reduce the amount of Ca2+ cycled during contraction and relaxation. The functional effects are prominent in heterozygotes of the genetically modified flies and mice whereas the loss-of-function in Drosophila TnT and gain-of-function in 51E-cTnT and Tx9-fsTnT mice both produced homozygote lethality, indicating sensitive dose effects of the myofilament Ca2+ reservoir for use as a potent mechanism to improve energetic efficiency of cardiac and skeletal muscles.

A rational approach to selective targeting of skeletal myosin.

Altered actin-myosin binding in the sarcomere has been linked to congenital skeletal and cardiac myopathies characterised by muscular weakness.1Since the discovery of omecamtiv mecarbil (OM)2, the direct targeting of the myosin II motor protein has been considered as a promising strategy to restore normal muscle function. While there has been success in the development of cardiac myosin drugs, with one of them recently achieving FDA approval,3 selective targeting of skeletal myosin has been less explored. Here, we used a range of molecular modelling techniques to compare the structure and dynamics of the OM binding site in cardiac and in fast type IIa skeletal myosin.4 We found important differences in the shape and size of the binding pocket in the two isoforms, which we relate to small but significant differences in its amino acidic composition. Moreover, inclusion of protein dynamics turned out to be essential to explain the observed selectivity of OM for the cardiac isoform. Information from our modelling is currently being used to identify novel compounds that can selectively bind skeletal myosin, and potentially treat congenital myopathies where muscle weakness is related to myosin loss-of-function.

Stress effect on the mandibular dental arch by mentalis muscle over activity, finite element analysis.

The perioral muscles postural and functional abnormality should be clearly evaluated. The influence of the abnormal function of mentalis muscle on the shape and posture of the mandible was evaluated using a finite element approach. Finite element analysis was used to create a three-dimensional representation of a human mandible that represents a dry normal mandible with teeth (33-36 gm/cm2). Pressures were applied directly to the labial surface of the mandible's lower anterior dento-alveolar structure reflecting the normal lips muscle function. While on abnormal swallowing pattern, lip muscle force (300 gm\cm2) had been assumed. Shape and postural abnormality of the mandible with malocclusion particularly at the anterior dentoalveolar and basal bone region in sagittal direction as well as inward pressure on the mandibular posterior region. Abnormal perioral muscle function throughout growth and development may result in a shape and postural abnormality of the mandible and a companying malocclusion.

Spatial and temporal requirement of Mlp60A isoforms during muscle development and function in Drosophila melanogaster

Many myofibrillar proteins undergo isoform switching in a spatio-temporal manner during muscle development. The biological significance of the variants of several of these myofibrillar proteins remains elusive. One such myofibrillar protein, the Muscle LIM Protein (MLP), is a vital component of the Z-discs. In this paper, we show that one of the Drosophila MLP encoding genes, Mlp60A, gives rise to two isoforms: a short (279 bp, 10 kDa) and a long (1461 bp, 54 kDa) one. The short isoform is expressed throughout development, but the long isoform is adult-specific, being the dominant of the two isoforms in the indirect flight muscles (IFMs). A concomitant, muscle-specific knockdown of both isoforms leads to partial developmental lethality, with most of the surviving flies being flight defective. A global loss of both isoforms in a Mlp60A-null background also leads to developmental lethality, with muscle defects in the individuals that survive to the third instar larval stage. This lethality could be rescued partially by a muscle-specific overexpression of the short isoform. Genetic perturbation of only the long isoform, through a P-element insertion in the long isoform-specific coding sequence, leads to defective flight, in around 90% of the flies. This phenotype was completely rescued when the P-element insertion was precisely excised from the locus. Hence, our data show that the two Mlp60A isoforms are functionally specialized: the short isoform being essential for normal embryonic muscle development and the long isoform being necessary for normal adult flight muscle function.