Tetanic Tension Research Articles

Influence of Simulated Microgravity on Mechanical Properties in the Human Triceps Surae Muscle in vivo

Purpose. The aim of the study was to investigate the effects of a simulated microgravity on the mechanical properties of the human triceps surae (TS) and to assess the effectiveness of physical training (PT) in preventing detrimental effects. Methods. Eight women (aged 26-36 years) underwent 120-d of Bed rest (BR): four underwent Bed rest only (BR group) and four performed PT during this period (BRPT group). The training sessions were conducted for 60 min each day for 6 days a week for 14 weeks, and 30-40 min twice a day for 2 weeks under the experiment conditions. PT was performed over a 4-d cycle: 3-d of training and 1-d of rest. The maximal voluntary contraction (MVC), and isometric twitch contraction (Pt), and electrically evoked tetanic tension at 150 impulses × s -1 (Ро), time-to-peak tension (TPT) of the twitch were determined. The difference between Ро and MVC expressed as a percentage of Ро and referred to a force deficiency (Рd). The MTS was determined according to the electromechanical delay (EMD) value during the explosive voluntary contraction. Surface electrodes sensed electromyographic (EMG) activity in the soleus muscle. Electromechanical delay (EMD) was the time interval between the change in EMG and movement muscle force production. Results. In the BR group, Рt, MVC, and Ро had decreased by 12, 36, 24%, respectively, but Рd had increased by 39%. TPT of the twitch had increased by 14%. The rate of increase of voluntary contractions reduced, but in the electrically evoked contraction no changes were observed. The EMD had increased by 27%. In the BREx group, МVС, Рt, and Ро decreased by 3%, and 14%, and 9%, respectively. TPT had decreased by 4%. The Pd had decreased significantly by 10%. The rate of rise increase of electrically evoked tetanic did not change significantly, but the rate of rise in isometric voluntary tension development was increased. The EMD had decreased by 12%. Conclusion. Unloading decreased function and EMD muscle and, although the PT did attenuate these effects, they did not completely prevent them. It is suggested that the total loading volume (mainly its intensity) was not sufficient to completely prevent alterations in tendon mechanical properties

Low-dose ouabain administration increases Na+,K+-ATPase activity and reduces cardiac force development in rats

BackgroundOuabain is a digitalis compound that inhibits the Na+,K+-ATPase (NKA) activity inducing increment in cardiac force. However, this effect seems to be dose dependent. At low concentration, ouabain can induce an increase of NKA activity. MethodsWe investigated the effects of ouabain administration (25μg/kg/day) for 15 days on cardiac contractility and NKA activity. Blood pressure and left ventricular papillary muscle contraction from placebo and ouabain-treated rats for 15 (OUA15) days were evaluated. Isometric force, post-rest potentiation, positive inotropic intervention produced by isoproterenol, and tetanic tension were measured. The activity and protein expression levels of α1 and α2 isoforms of NKA, sodium calcium exchanger (NCX), sarcoplasmic reticulum calcium ATPase (SERCA2a) and phospholamban (PLB) were also measured. ResultsSystolic and diastolic blood pressures increased after treatment with ouabain. However, isometric tension was reduced in the ouabain treated group. Post-rest potentiation, time parameters, inotropic interventions by isoproterenol and tetanic tension did not change. In the ouabain treated group, NKA activity was increased (Oua 406.16±70.6 vs. CT 282.80±80.5) while protein expression of the α1 isoform of NKA was reduced (Oua 0.97±0.06 vs. CT 0.76±0.05). No changes were observed in protein expression of α2 isoform of NKA, NCX, SERCA2a and PLB. Therefore, although 15-day ouabain treatment increases blood pressure (Oua: 116.4±3 vs. CT: 99.9±3), treatment also reduces isometric tension development (Oua: 0.34±0.14 vs. CT: 0.56±0.22). ConclusionWe suggest that the effects induced by ouabain in the isolated cardiac muscle could be related at least in part, to changes in NKA activity.

Prolonged Administration of Pyridostigmine Impairs Neuromuscular Function With and Without Down-Regulation of Acetylcholine Receptors

Richtsfeld, Martina*†; Yasuhara, Shingo*; Fink, Heidrun‡; Blobner, Manfred‡; Jeevendra Martyn, J. A.* Author Information

Effect of Ginkgo Biloba Extract on Contractility Enhancement of Diaphragm of Rats with Type 2 Diabetes

To investigate the effects of Ginkgo biloba extract (GbE) on the activities of energy metabolism enzymes and contraction capacity of diaphragm from type 2 diabetic rats. Forty SD mile rats were randomly divided into normal control group (n=10) and model group (n=30). Type 2 diabetes models were induced by feeding with high-sucrose-high-fat diet and intraperitoneal injecting 25mg/kg streptozotocin. 20 successful models were rearranged to two groups: diabetic group and GbE treatment group, 10 rats in each. Then the saline and 8mg·kg-1·d-1 of GbE were respectively intraperitoneal injected, once a day continuously for 8 weeks. Then diaphragm contractility was assessed using Peak twitch tension (Pt), Maximum tetanic tension (P0) and fatigue index (FI) in vitro diaphragm strip preparations. Cytochrome oxidase (CCO), lactate dehydrogenase (LDH) and succinate dehydrogenase (SDH) in diaphragm were detected and the varieties of diaphragm ultrastructure were observed. Compared with control group, Pt, P0 and FI in diabetic group decreased significantly (P < 0.01); the activity of CCO, LDH and SDH in the tissues was obviously reduced than those in control group (P < 0.01). The ultrastructure in diabetic group under electron microscope indicated that diaphragm mitochondrions swelled and degenerated. The above changes were inhibited by GbE. GbE can enhance contraction capacity of diaphragm from type 2 diabetic rats by increasing the aerobic oxidation capacity, glycolytic capacity and the function of respiratory chain.

O10: Effect size of quantitative muscle imaging in Duchenne muscular dystrophy exceeds the effect size of clinical scores of muscle function

s of Oral Presentations / Clinical Neurophysiology 125, Supplement 1 (2014) S1–S339 S31 confirmed Duchenne muscular dystrophy. Physical assessment was performed using the motor function measurement (MFM) scale. Quantitative magnet resonance imaging (qMRI) of thigh muscles was performed using the two-point Dixon method. One year functional and imaging changes were different according to the age and walking abilities at inclusion (group 1: below the age of seven; group 2: seven years and older and ambulant; group 3: non-ambulant). While patients of the first group still showed improvement of motor abilities, in group 2 the largest effect size (1.2) was found in the D1 subscore (standing and transfer function) of the MFM, and in group 3 the largest effect size was found for the total MFM score (0.66). In contrast, the effect sizes using qMRI was much larger consisting of 1.6 in group 1 (all thigh muscles), 4.1 in group 2 (hamstrings), and 2.3 in group 3 (knee extensors). These data suggest that qMRI has an added value compared to clinical outcome measures when designing therapeutic clinical trials in patients with DMD. Power analysis suggest that there are only a few needed patients to show an effect of a putative novel treatment when using quantitive muscle MRI in DMD. O11 Estimation of the muscle fiber density from the motor unit action potential I. Goker1, T. Artug2, O. Osman2, B. Baslo3 1Istanbul Arel University, Biomedical Engineering, Istanbul, Turkey; 2Istanbul Arel University, Electrical and Electronics Engineering, Istanbul, Turkey; 3Istanbul University, Medical Faculty, Istanbul, Turkey Introduction: The aim of this study is the estimation of the muscle fiber density (FD) from the Motor Unit Action Potentials (MUAP) to form a method for monitoring the progress of neuromuscular diseases. Methods: Data groups representing motor units of neurogenic (n=5), myopathic (n=5) and healthy cases (n=5) were created via EMG Simulator v3.6. MUAPs generated from each data group have been detected through a concentric needle electrode of a scanning EMG system. The spikes of the single fiber action potentials within the MUAPs have been found by computing the second-order derivative of MUAPs to estimate the detected number of fibers. MUAPs from 20 different locations within a Motor Unit Territory (MUT) have been acquired. The fiber density (FD) has been computed by taking the average of these numbers of fibers. True FDs have been computed for each MUT. Mean Square Errors (MSE) have been computed for each data group to determine the sensitivity of the method. Results: The test statistics of the FDs (mean ± SD) have been found as 4.13±1.31 (Min: 2 and Max: 8), 2.37±0.98 (Min: 1 and Max: 5) and, 2.40±0.70 (Min: 1 and Max: 4) for neurogenic, myopathic and healthy cases respectively. Mean true fiber densities have been 5.66, 2.57 and 1.50 and MSE have been 4.02, 0.15 and, 0.86 for neurogenic, myopathic and healthy cases respectively. These MSE values have been suggested that this method is more selective for myopathic cases compared to neurogenic and healthy cases. Conclusion: Computation of FD via the second-order derivative of MUAPs can be considered as a beneficial preliminary research. Nevertheless, this method might be extended by taking into account other variables such as maximum amplitude to increase the sensitivity for neurogenic cases.

Effects of lipopolysaccharide‐induced systemic inflammation on the contractile properties of the fast twitch extensor digitorum longus muscle in mice (1102.19)

Chronic sepsis, which includes a large inflammatory response, leads to muscle wasting, decreased muscle contractile forces and an increase in fatigability (Lanone, et al., 2005; Rossignol, et al., 2008). The effects of lower levels of systemic inflammation on muscle contractile properties have not been well studied. We tested the hypothesis that contractile properties of skeletal muscles are altered by lower levels of systemic inflammation using an in vitro adult mouse extensor digitorum longus muscle preparation. We tested the response to inflammation caused by a high dose of lipopolysaccharide (LPS; 7.5 x 10^5 Endotoxin Units/ kg IP 18 hrs before sacrifice; n=6) with or without a 1 month exposure to low LPS (7.5 x 104 EU/kg; 2/wk, n=4). Controls were given a saline injection 18 hrs before sacrifice (n=6). Twitch and tetanic contractions were induced by bath electrodes and a 10 min fatigue test (.5 ms pulse width, 60 Hz, 350 ms train at supramaximal voltage every 3 s) was performed. Muscle contractile properties including time to peak contraction, half‐relaxation time and fatigue index (40th train tension/maximal tetanic tension) were not significantly different from control values following high LPS, even when it was preceded by a month of low LPS. Future studies will increase the sample size and confirm that LPS‐induced systemic inflammation at our doses does not alter contractile properties.Grant Funding Source: Supported by a CSUPERB President's Commission Fellowship (RGM) and a CSUPERB New Investigator (KAW)

Diaphragmatic Function Is Preserved during Severe Hemorrhagic Shock in the Rat

Acute diaphragmatic dysfunction has been reported in septic and cardiogenic shock, but few data are available concerning the effect of hemorrhagic shock on diaphragmatic function. The authors examined the impact of a hemorrhagic shock on the diaphragm. Four parallel groups of adult rats were submitted to hemorrhagic shock induced by controlled exsanguination targeting a mean arterial blood pressure of 30 mmHg for 1 h, followed by a 1-h fluid resuscitation with either saline or shed blood targeting a mean arterial blood pressure of 80 mmHg. Diaphragm and soleus strip contractility was measured in vitro. Blood flow in the muscle microcirculation was measured in vivo using a Laser Doppler technique. Muscle proinflammatory cytokine concentrations were also measured. Hemorrhagic shock was characterized by a decrease in mean arterial blood pressure to 34 ± 5 mmHg (-77 ± 4%; P< 0.05) and high plasma lactate levels (7.6 ± 0.9 mM; P < 0.05). Although tetanic tension of the diaphragm was not altered, hemorrhagic shock induced dramatic impairment of tetanic tension of the soleus (-40 ± 19%; P < 0.01), whereas proinflammatory cytokine levels were low and not different between the two muscles. Resuscitation with either blood or saline did not further modify either diaphragm or soleus performance and proinflammatory cytokine levels. The shock-induced decrease in blood flow was much more pronounced in the soleus than in the diaphragm (-75 ± 13% vs. -17 ± 10%; P = 0.02), and a significant interaction was observed between shock and muscle (P < 0.001). Diaphragm performance is preserved during hemorrhagic shock, whereas soleus performance is impaired, with no further impact of either blood or saline fluid resuscitation.

The effect of heat stress on skeletal muscle contractile properties

An elevated heat-shock protein (HSP) content protects cells and tissues, including skeletal muscles, from certain stressors. We determined if heat stress and the elevated HSP content that results is correlated with protection of contractile characteristics of isolated fast and slow skeletal muscles when contracting at elevated temperatures. To elevate muscle HSP content, one hindlimb of Sprague-Dawley rats (21-28days old, 70-90g) was subjected to a 15min 42°C heat-stress. Twenty-four hours later, both extensor digitorum longus (EDL) and soleus muscles were removed, mounted in either 20°C or 42°C Krebs-Ringer solution, and electrically stimulated. Controls consisted of the same muscles from the contra-lateral (non-stressed) hindlimbs as well as muscles from other (unstressed) animals. Isolated muscles were twitched and brought to tetanus every 5min for 30min. As expected, HSP content was elevated in muscles from the heat-stressed limbs when compared with controls. Regardless of prior treatment, both EDL and soleus twitch tensions were lower at 42°C when compared with 20°C. In addition, when incubated at 42°C, both muscles showed a drop in twitch tension between 5 and 30min. For tetanic tension, both muscles also showed an increase in tension between 5 and 30min when stimulated at 20°C regardless of treatment but when stimulated at 42°C no change was observed. No protective effect of an elevated HSP content was observed for either muscle. In conclusion, although heat stress caused an elevation in HSP content, no protective effects were conferred to isolated contracting muscles.

Adiponectin alleviates contractile dysfunction of genioglossus in rats exposed to chronic intermittent hypoxia

Background Genioglossal dysfuntion takes an important role in pathogenesis of obstructive sleep apnea hypopnea syndrome (OSAHS) in which chronic intermittent hypoxia (CIH) is the major pathological origin. Recent studies have suggested genioglossal injury induced by CIH might be improved by adiponectin. The aim of this study was to investigate the effects of adiponectin on genioglossus contractile properties in rats exposed to CIH. Methods Thirty-nine healthy male Wistar rats were randomly divided into three groups: normal control (NC), CIH and adiponectin supplement (CIH+Ad) with 13 rats in each. Rats in NC were kept breathing normal air, while rats in CIH and CIH+Ad experienced the same CIH environment eight hours per day for 35 successive days. Rats in CIH+Ad were given intravenous adiponectin of 10 μg twice a week for 30 successive days. Rats in the NC and CIH were injected with normal saline as a control. After 35 days' CIH exposure, the levels of serum adiponectin and genioglossus contractile properties were compared. Results Serum adiponectin level was significantly lower in CIH than in NC (1210 ng/ml vs. 2236 ng/ml). Serum adiponectin level in CIH+Ad (1844 ng/ml) was significantly higher than CIH but lower than NC. Twitch tension, time to peak tension, half relaxation time and tetanic tension were significantly lower in CIH than NC and improved in CIH+Ad. All mean tetanic fatigue indices decreased more rapidly in the first 20 seconds than during the subsequent 100 seconds. Tetanic fatigue indices in NC and CIH+Ad were significantly higher compared to CIH. Conclusions CIH could lead to hypoadiponectinaemia, impaired genioglossus contractile properties and decreased fatigue resistance in rats. Such changes could be partially offset by supplementation of adiponectin.

Nonsurgically induced disuse muscle atrophy and neuromuscular dysfunction upregulates alpha7 acetylcholine receptors

Previous models of muscle disuse have invariably used surgical methods that require the repetitive application of plaster casts. A method of disuse atrophy that does not require such repetitive applications is described herein. Modified plastic pipette tubing was applied to a single hindlimb (mouse), from thigh to foot, resulting in immobilization of the knee in the extension position, and the ankle in the plantar flexion position. This method resulted in the loss of soleus muscle to 11%, 22%, 39%, and 45% of its original mass at 3, 7, 14, and 21 days, respectively, in association with a significant decrease of tibialis twitch (25%) and tetanic tensions (26%) at 21 days, compared with the contralateral side and (or) sham-immobilized controls. Immunohistochemical analysis of the soleus using fluorescent α-bungarotoxin revealed a significant increase in the number of synapses per unit area (818 + 31 compared with 433 + 16/mm(2)) and an increase in muscle fibers per unit area (117 compared with 83/mm(2)), most likely related to the atrophy of muscle fibers bringing synapses closer. A 3-fold increase in alpha7 acetylcholine receptor (α7AChR) protein expression, along with increased expression of α1AChR subunit in the immobilized side compared with the contralateral side was observed. The physiology and pharmacology of the novel finding of upregulation of α7AChRs with disuse requires further study.

Prolonged Administration of Pyridostigmine Impairs Neuromuscular Function with and without Down-regulation of Acetylcholine Receptors

The acetylcholinesterase inhibitor, pyridostigmine, is prophylactically administered to mitigate the toxic effects of nerve gas poisoning. The authors tested the hypothesis that prolonged pyridostigmine administration can lead to neuromuscular dysfunction and even down-regulation of acetylcholine receptors. Pyridostigmine (5 or 25 mg·kg·day) or saline was continuously administered via osmotic pumps to rats, and infused for either 14 or 28 days until the day of neuromuscular assessment (at day 14 or 28), or discontinued 24 h before neuromuscular assessment. Neurotransmission and muscle function were examined by single-twitch, train-of-four stimulation and 100-Hz tetanic stimulation. Sensitivity to atracurium and acetylcholine receptor number (quantitated by I-α-bungarotoxin) provided additional measures of neuromuscular integrity. Specific tetanic tensions (Newton [N]/muscle weight [g]) were significantly (P < 0.05) decreased at 14 (10.3 N/g) and 28 (11.1 N/g) days of 25 mg·kg·day pyridostigmine compared with controls (13.1-13.6 N/g). Decreased effective dose (0.81-1.05 vs. 0.16-0.45 mg/kg; P < 0.05) and decreased plasma concentration (3.02-3.27 vs. 0.45-1.37 μg/ml; P < 0.05) of atracurium for 50% paralysis (controls vs. 25 mg·kg·day pyridostigmine, respectively), irrespective of discontinuation of pyridostigmine, confirmed the pyridostigmine-induced altered neurotransmission. Pyridostigmine (25 mg·kg·day) down-regulated acetylcholine receptors at 28 days. Prolonged administration of pyridostigmine (25 mg·kg·day) leads to neuromuscular impairment, which can persist even when pyridostigmine is discontinued 24 h before assessment of neuromuscular function. Pyridostigmine has the potential to down-regulate acetylcholine receptors, but induces neuromuscular dysfunction even in the absence of receptor changes.

The effects of bupivacaine injection and oral nitric oxide on extraocular muscle in the rabbit

Nitric oxide (NO) plays a key role in muscle regeneration, which is the primary response, observed during bupivacaine-induced extraocular muscle (EOM) hypertrophy. Our aims were to investigate the effects of bupivacaine injection into the rabbit EOM and the interaction with NO. Superior rectus (SR) muscles of 24 New Zealand albino rabbits were studied. Single muscle twitch tension (SMTT) and tetanic muscle tensions at 50, 75, and 100 Hz were recorded using a 15 V stimuli. The rabbits were equally allocated into three groups. Measurements were performed without any drug treatments in group 1. In groups 2 and 3, bupivacaine, 0.5 ml of a 0.50 % solution, was injected into the EOM, and after 21 days, measurements were performed. Oral isosorbide dinitrate (NO donor) at 20 mg/day was given each day prior to measurements in group 3. SMTTs were 69.9 (66.7-77.6), 187.7 (114.9-252.1) and 204.2 (135.3-311.6) mg in groups 1, 2, and 3 respectively. SMTTs for both groups 2 and 3 were significantly higher than that for group 1 (p < 0.05). Compared with group 1, group 2 exhibited a 3.8-11.7 % increase in the tetanic tensions at 50, 75, and 100 Hz, but none of these differences were statistically significant. The increase was 47.5-137.5 % in group 3 relative to group 2, and the differences were statistically significant except at 100 Hz. The enlargement of the muscle fibers after bupivacaine injection was shown histopathologically. Bupivacaine injection increased the EOM tension in rabbits to some extent. NO augmented the effect of bupivacaine.

Изменение сократительных свойств трехглавой мышцы голени и электромеханической задержки под влиянием 120-суточной моделируемой микрогравитации с использованием физической тренировки

The effect of a 120-day -5 degrees head-down tilt (HDT) bed rest with countermeasures (physical training) on the mechanical properties of the human triceps surae muscle was studied in four healthy young women aged 28.0. The results showed that the contractile properties of the skeletal muscle studied changed considerably. After HDT without countermeasures the maximal voluntary contraction (MVC) had decreased by 36% (P < 0.05), and the electrically evoked tetanic tension at 150 Hz (P) and isometric twitch contraction (P(t)) had decreased by 24% (P < 0.05) and 12 % (P < 0.05), respectively. Time-to-peak tension (TPT) of the twitch had significantly increased by 14% (P < 0.05), but half-relaxation time (1/2 RT), and total contraction time (TCT) had decreased by 19% (P < 0.05) and 18% (P < 0.05), respectively. The difference between P(o) and MVC expressed as a percentage of P(o) and referred to as force deficiency (P(d)), was also calculated. The P(d) had increased by 40% (P < 0.001). The rate of increase of voluntary contractions calculated according to a relative scale had significantly reduced, but for the electrically evoked contraction no substantial changes were observed. After HDT with countermeasures TPT, 1/2 RT and TCT had decreased by 4%, 7%, 19%, respectively in relation to the control condition. Training had caused a decrease of 3% (P > 0.05) in MVC, and P(t) and in P(o) of 14%, and of 9% (P > 0.05), respectively. The Pd had decreased significantly by 10% (P < 0.05). The rate of increase of electrically evoked tetanic tension did not change significantly during HDT with countermeasures but the rate of increase in isometric voluntary tension development was increased. Physical training provided a reserve of neuromuscular function, which attenuated the effect of bed rest. The experimental findings indicated that neural as well as muscle adaptation occurred in response to HDT with countermeasures.

Modulation of Skeletal Muscle Performance and SERCA by Exercise and Adiponectin Gene Therapy in Insulin-Resistant Rat

This study addresses the potential application of adiponectin gene therapy and exercise in protection against skeletal muscle dysfunction in type 2 diabetes mellitus (T2DM) while focusing on the role of sarco and endoplasmic reticulum Ca(+2) ATPase (SERCA) and Glut4. 50 rats were divided into five groups: control, T2DM, T2DM treated with either adiponectin gene or exercise or a combination of both. Serum glucose, insulin, HOMA index, triglycerides, and cholesterol were measured. Weight gain%, muscle contractile parameters {(peak twitch tension (Pt), peak tetanic tension (PTT), half relaxation time (HRT)}, and gene expression of SERCA, Glut4, and adiponectin were assessed in gastrocnemius muscle. Diabetic rats treated with either adiponectin gene or exercise showed significant reduction in all serum parameters and wt gain%. There was significant elevation in Pt and PTT with shortening in HRT. Furthermore, a significant increase in SERCA, Glut4, and adiponectin gene expression was noticed in both groups. Combination therapy caused marked gene expression of SERCA, GLUT4, and greater improvement in muscle contractility than either of the monotherapies. Skeletal muscle dysfunction in T2DM is mediated via impaired SERCA and Glut 4. Combination therapy offered best protection against muscle dysfunction and provides a novel promising strategy for a complete cure of muscle dysfunction in T2DM.

The Effectiveness of Contralateral C7 Nerve Root Transfer for the Repair of Avulsed C7 Nerve Root in Total Brachial Plexus Injury: An Experimental Study in Rats

The aim of this study was to evaluate the feasibility and effectiveness of transferring the contralateral C7 root to repair avulsed C7 nerve root. Thirty rats were randomized into three groups. In group A, rats underwent whole-root avulsion of the left brachial plexus and contralateral C7 root transfer to the avulsed C7 nerve root. In group B, rats underwent whole-root avulsion and contralateral C7 root transfer to the radial nerve. In group C, rats underwent whole-root avulsion of the left brachial plexus without nerve transfer. Functional outcomes were measured by electrophysiological studies, muscle tetanus contraction force, muscle mass, and histology. Six months postoperatively, increased amplitude and shortened latency of compound muscle action potentials, larger maximum tetanic contractile tension, heavier muscle mass, and larger cross-sectional area of the muscle fibers were observed in the triceps, extensor carpi radialis brevis, and extensor digitorum in groups A and B when compared with group C (p < 0.01). There were no significant differences between group A and B (p > 0.05). Contralateral C7 nerve transfer to repair avulsed C7 nerve root was feasible and effective in this rat model. It should be considered as an option for the treatment of brachial plexus injuries.

The effect of mesenchymal stem cells in a PEGylated fibrin gel seeded on an extracellular matrix on skeletal muscle recovery in a volumetric muscle loss model

This study investigated the effect of mesenchymal stem cells (MSCs) in a PEGylated fibrin gel (PEG) seeded into an acellular extracellular matrix (ECM) on recovery of skeletal muscle following volumetric muscle loss (VML) injury. Approximately 1/3 of the mass of the lateral gastrocnemius (LGAS) was removed from 6–9 month male Sprague‐Dawley rats, and immediately replaced with an ECM of the same dimensions. One week later, animals were injected with: saline (SAL), MSCs, PEG, or MSCs in PEG (PEG+MSC). Fifty‐six days after injury, LGAS maximal isometric tetanic tension (Po) of the PEG+MSC treated group was significantly higher compared to all other treatments due to greater mass. The specific tension (N/cm2) however, was only significantly higher compared to SAL and PEG groups. Myofiber cross‐sectional area (CSA) was evaluated throughout the implanted scaffold. Cell‐treated groups trended towards a greater percentage of larger myofibers compared to SAL and PEG groups. These findings suggest that MSCs provide the main regenerative stimulus when infused at 7 days, and demonstrates their importance in regeneration in VML injury models. Functional assessments via neural stimulation demonstrated neural regeneration, however long–term viability is yet to be determined.

Investigation of Bisphenol A administration on skeletal muscle force generation in mice

Bisphenol A (BPA) is a chemical used in the manufacturing of numerous products including plastics and food‐contact materials and is classified as an endocrine disruptor because it can mimic actions of estrogen in the body. The purpose of this study was to examine BPA effects on muscle force generation since estrogen may influence muscle contractile properties. Eight‐week old male CD‐1 mice were housed in polypropylene cages and provided a soybean oil‐free diet (AIN‐93G) (control; C) for two weeks. Thereafter, animals were randomly assigned to C (n=5), C+BPA (BPA; 50 mg BPA/kg diet; n=4), or C+ethinyl estradiol (EE; 0.1 ppb; n=5) diets for one month. Soleus muscles were harvested for measurement of twitch and tetanic force generation (N/cm2) in vitro. Peak twitch tension of EE (3.5±0.1) was greater (p&lt;0.05) than BPA (2.6±0.1) and C (2.8±0.2). Peak tetanic tension of EE (24.8±1.2) was greater (p&lt;0.05) than BPA (19.2±0.7) but was similar (p&gt;;0.05) to C (22.31±0.3). Soleus force generation between BPA and C was similar (p&gt;;0.05). Post‐experiment animal body mass and soleus muscle mass did not differ between groups (p&gt;;0.05). Preliminary findings revealed augmented force generation of the soleus following administration of EE, but not BPA. Therefore, BPA administration does not appear to influence twitch or maximal force generation of mouse soleus muscle.Supported by the Hill Collaboration on Environmental Medicine (KCD)

Train-of-Four and Tetanic Fade Are Not Always a Prejunctional Phenomenon as Evaluated by Toxins Having Highly Specific Pre- and Postjunctional Actions

Nerve-stimulated fade in muscle is generally accepted as a prejunctional phenomenon mediated by block of prejunctional acetylcholine receptors (AChRs) at the nerve terminal, whereas decrease of twitch tension is considered a postjunctional effect due to block of muscle AChRs. Using ligands with specific pre- or postjunctional effects only, we tested the hypothesis that fade is not necessarily a prejunctional phenomenon. Neuromuscular function in rats was evaluated after IM (2.5 U) or IV (12.0 U) injection of botulinum toxin (Botx), or IV (250 μg/kg) α-bungarotoxin (α-BTX) alone. The acute neuromuscular effects of IV 2 mg/kg dihydro-β-erythroidine (DHβE), alone and in combination with α-BTX, were also tested. Botx decreases vesicular release of ACh, and α-BTX binds to postjunctional nicotinic AChRs only, whereas DHβE binds specifically to prejunctional α3β2 AChRs only. In view of the lack of acute effects of Botx even at 2 hours after IV injection, its neuromuscular effects were also evaluated at 24 hours after IM injection (0.6 U) and compared with IM injection of α-BTX (25 μg/kg) or saline also given 24 hours earlier. The sciatic nerve-tibialis muscle preparation, during train-of-four and tetanic stimulation, was used to test neuromuscular effects in vivo. IV and IM Botx had no observable neuromuscular effects at 2 hours. IV α-BTX caused twitch depression within a few minutes, and significant fade (P = 0.002) at 75% of baseline twitch tension; these effects persisted until the end of the observation period of 2 hours. IV DHβE alone caused no significant change in single twitch (P = 0.899) or train-of-four ratio (P = 0.394), but significantly enhanced the fade of IV α-BTX (P = 0.001 at 75% of baseline twitch tension). IM Botx or α-BTX, at 24 hours after their injection, resulted in a significant decrease of single twitch and tetanic tensions (P < 0.0001), but Botx did not cause fade, whereas α-BTX caused significant (P < 0.0001) fade at 24 hours. The tibialis muscle weights and protein expression of α1 subunit of AChR (Western blots) did not differ between Botx, α-BTX and saline-injected groups at 24 hours but increased in denervated muscle (positive control). Botx-induced decreased ACh release in and of itself does not cause fade but does cause decrease of absolute tensions. Decrease of available (functional) postjunctional AChRs by α-BTX did induce fade. The prejunctional fade effects of DHβE on α3β2 AChRs become manifest only when the margin of safety was decreased by concomitant administration of α-BTX. Thus, fade during repetitive stimulation is not always a prejunctional phenomenon and may also reflect the decreased margin of safety of neurotransmission, which can be due to a pure postjunctional AChRs block or to a combination of both pre- and postjunctional AChRs block. Block of prejunctional α3β2 AChRs alone is not necessary and sufficient to cause fade.

Serum levo-carnitine levels and skeletal muscle functions in type 2 diabetes mellitus in rodents.

To study serum levo-carnitine (l-carnitine) levels and isometric contraction, force frequency relationship and fatigue of rodent skeletal muscles in type 2 diabetes mellitus. Randomized controlled trial. Physiology Department, Army Medical College, Rawalpindi, from January 2009 to January 2010. Sixty Sprague-Dawley rats were randomly divided into two groups; group I (control), fed on normal diet ad libitum and Group II (diabetic), fed on high fat diet and administered streptozocin to induce type 2 diabetes mellitus (T2DM). At 21st day, plasma glucose and TG/HDL ratio were measured to confirm the development of T2DM in group II. At 28th day, blood was drawn by intracardiac puncture to estimate serum levo-carnitine levels. Contractile functions of skeletal muscles were assessed by using iWorx AHK/214 physiological data acquisition unit. Simple muscle twitches, maximum isometric twitch tension (MITT), time-to-peak twitch tension (TPTT) and time-to-relax to 50% of the peak twitch tension (1/2RT) of extensor digitorum muscles were recorded. Muscles were stimulated at higher frequencies to determine maximum fused tetanic tension (MFTT), maximum fused tetanic tension after fatigue protocol (TTFP) and recovery from fatigue (RF). Serum levo-carnitine level decreased significantly in the diabetic group. Both groups had similar MITT, TPTT and 1/2RT but decline in MFTT, TTFP and RF was significant in the diabetic rats. T2DM adversely affected serum levo-carnitine levels and the contractile functions of rodent skeletal muscle at high frequency stimulation.

Levo-carnitine reduces oxidative stress and improves contractile functions of fast muscles in type 2 diabetic rats.

Metabolic derangements in type 2 diabetes mellitus (T2DM) are likely to affect skeletal muscle contractile functions adversely. Levo-carnitine improves muscle contractile functions in healthy humans and rats and corrects metabolic derangements in T2DM. Therefore, it is likely to improve muscle contractile functions in T2DM as well. This study was designed to determine the effect of levo-carnitine on serum levo-carnitine levels, oxidative stress and contractile parameters of fast muscle in T2DM. Ninety Sprague-Dawley rats were randomly divided into three equal groups. Healthy rats served as the controls, while T2DM was induced in diabetic and carnitine groups. The carnitine group was administered levo-carnitine 200 mg/kg/day intraperitoneally for 6 days. At 28th day, extensor digitorum longus muscles were removed and their functions were assessed using iWorx data acquisition unit (AHK/214). Blood obtained by intra-cardiac sampling at 28th day was used for estimation of serum malondialdehyde (MDA) and levo-carnitine levels. Maximum isometric twitch tension, time-to-peak twitch tension and time-to-relax to 50% of the peak twitch tension were not significantly different amongst the groups. Carnitine group showed significant improvement in maximum fused tetanic tension, maximum fused tetanic tension after fatigue protocol and recovery from fatigue after 5 minutes of rest period compared to the diabetic group. Serum MDA levels were reduced, while serum levo-carnitine levels were elevated significantly in carnitine group as compared to the diabetic group. Levo-carnitine supplementation increases serum levo-carnitine levels which decreases oxidative stress. This action improves contractile force but delays fatigue in fast muscles of diabetic rats.