Time To Peak Tension Research Articles

Эффекты кардиотоксинов кобры на папиллярной мышце и сердце крысы, перфузируемом по Лангендорфу, не связаны с выбросом адреналина

In a study of the effects of cobra cardiotoxins on myocardial tissue, both right ventricular (papillary muscle) and left ventricular contractility (isovolumic recording of left ventricular pulse pressure during Langendorff perfusion of the heart) were assessed. In papillary muscle, both toxins, at a concentration of 5 μg/mL, caused short-term increases in contractility to 200±25% and 171±15% for CTX-1 and CTX-2, respectively, at the point of maximum effect. At the same time, for CTX-1 and CTX-2, the time to peak tension (TPT) increased from 104±2 to 111±2 and from 96±2 to 104±5 ms, the relaxation time to 50%(TR50%) from 64±4 to 70±6 and from 64±6 to 69±7 ms, and the relaxation time to 95%(TR95%) from 163±10 to 190±22 and from 148±16 to 155±20 ms, respectively. This significantly differs from the positive inotropic effect of the β-adrenomimetic isoproterenol (170±31%), which causes acceleration of TPT from 106±5 to 89±4 ms, TR50% from 58±6 to 43±4 ms, and TR95% from 145±15 to 90±14 ms. When the whole heart was exposed to cardiotoxins, an increase in contractility was also observed, followed by its suppression and contracture, in contrast to isoproterenol, which caused a steady increase in contractility coupled with an increase in heart rate. Pretreatment of papillary muscles with the β-blocker propranolol 
 (10 μM) did not prevent the development of cardiotoxin effects, but completely blocked the effects of isoproterenol. Our data indicate that the temporary increase in contractility under the action of cardiotoxins is not associated with the release of endogenous adrenaline, but rather is caused by changes in calcium homeostasis in cardiomyocytes.

Swimming training attenuates the decrease of calcium responsiveness in female infarcted rats.

Aim: To evaluate the influence of swimming training on calcium responsiveness of the myocardium of rats with different infarction sizes (MI). Method: female Wistar rats, sedentary sham (SS = 14), sedentary moderate MI (SMI = 8) and sedentary large MI (SLI = 10) were compared to trained sham (TS = 16), trained moderate MI (TMI = 9) and trained large MI (TLI = 10). After 4 weeks of MI, the animals swam for 60 min/day, 5 days/week, for additional 8 weeks. Papillary muscles of the left ventricle were subjected to different concentrations of extracellular calcium. Inotropism was evaluated through the developed tension (DT), the maximum positive value of the first temporal derivation (+Td/td) and the time to peak tension (TPT). Lusitropism was evaluated by the maximum negative value of the first temporal derivation (−Td/td) and time to 50% relaxation (50%TR). Statistical significance was determined using multivariate analysis of variance and a Hotelling T2 test for the absolute power values of all four extracellular calcium concentrations (p < 0.05). Results: MI depressed inotropism (from 17% to 51%) and lusitropism (from 22% to 54%) of the sedentary rats, but exercise attenuated the losses, especially regarding + dT/dt, TPT, −dT/dt and 50%TR. Exercise attenuated the decrease in myocardial responsiveness, proportionally to the size of the MI. Conclusion: Myocardial calcium responsiveness is favorably affected in animals with moderate and large MI after swimming exercise.

Effect of Vitamin D Supplementation on Doxorubicin-Induced Cardiotoxicity in Rats

Abstract Background Doxorubicin-induced cardiotoxicity is a worldwide problem. Vitamin D is a well-known beneficial vitamin for bone growth and calcium homeostasis but recently it is also known for its cardioprotective effects. The aim of this study is to investigate the potential protective role of vitamin D on the cardiac dysfunction induced by chronic doxorubicin exposure, and to throw more light on the possible underlying mechanism (s) for such effect. Materials and Methods: 70 female Albino-rats were divided into 4 groups; control group (C), Doxorubicin-treated group (Dox): given i.p. injection of Dox in a dose of 2.5 mg/kg body weight (cumulative dose: 15 mg/kg) over 3 weeks, vitamin Dsupplemented group (Vit D): given vitamin D by oral gavage in a dose of 500 IU/kg daily, 5 days a week, also for 3 weeks and the combined Doxorubicintreated+vitamin D-supplemented group (Dox+Vit D). At the end of the experiment, ECG was recorded and in vitro isolated heart study was performed on Langendoroff preparation to measure peak tension (PT), time to peak tension (TPT), half relaxation time (HRT) and myocardial flow rate (MFR). Body and cardiac weights, plasma levels of brain naturetic peptide (BNP), cardiac troponin I (cTnI), vitamin D and total calcium and cardiac tissue heat shock protein 20, total antioxidant capacity (TAC) and malondialdehyde (MDA) were measured. Also, cardiac tissues were histopathologically assessed. Results: Dox-treated rats showed significant decrease in the final body weight (fBW), significant prolongation of the P-R interval, QRS duration, observed Q-T (Q-TO) and corrected Q-T (Q-Tc) with significant depression of the R voltage. In addition, there was a significant decrease in the in vitro heart rate, significant depression in PT, PT/LV and MFR together with significant prolongation in TPT&amp; 3 HRT. These changes were accompanied by significant elevation of plasma BNP, cTnI and in cardiac tissue MDA and a significant decrease in plasma vit D, total calcium and cardiac tissue TAC and HSP20. Histopathological examination revealed markedly distorted muscle fibers with indistinct cell borders, bright eosinophilic cytoplasm, intra-cytoplasmic vacuoles and small pyknotic nuclei or absent nuclei, together with interstitial edema &amp; aggregates of inflammatory cells and thick irregular collagen fibers in between the muscle fibers. Concomitant supplementation of vitamin D to the doxorubicin treated rats resulted in significant decrease in PR interval, QRS duration, MDA and significant increase PT, PT/LV, MFR, MFR/LV, plasma vitamin D, total calcium and TAC compared to the Dox treated rats to be insignificantly different from the control group. Plasma BNP and cTnI were significantly decreased while cardiac HSP20 was significantly increased compared to the Dox-treated rats, yet these parameters were still significant from the control group. Meanwhile, fBW, Q-TO and Q-Tc intervals, and TPT remained insignificantly changed from the DOX group. These findings were associated by regaining the normal collagen fiber distribution between cardiac muscle fibers with resolution of interstitial edema. Conclusion: Vitamin D supplementation can partially mitigate cardiac dysfunction induced by chronic doxorubicin by improving the cardiac antioxidant state and heat shock protein 20 level. Key words: Doxorubicin, cardiac dysfunction, vitamin D, isolated heart studies, BNP, HSP20.

A Possible Cardio-Protective Role of Early Remote Ischemia Preconditioning Against Ischemia Reperfusion Injury I’m Isolated Hearts of Adult Albino Rats: Possible Involvement of Hypoxia Inducible Factor

Abstract Background Inspite of the claimed cardio-protective effects of ischemic preconditioning (IPC), it is invasive and so using remote ischemic preconditioning (RIPC) may offer an alternative. Meanwhile, RIPC cardioprotective role is controversial, with an equivocal underlying mechanism. The hypoxia inducible factor 1 alpha (HIF-1-alpha) which is increased following ischemic insults is claimed as a humoral mediator for RIPC. Objective To investigate the effect of remote ischemic pre-conditioning on myocardial ischemia/reperfusion injury in rats, and to elucidate the possible role of hypoxia inducible factor in this protection. Materials and Methods The present study was performed on 28 adult female albino rats in the same estrus cycle evaluated by vaginal smear, and they were allocated into 3 groups: Group I: control rats subjected to ischemic/reperfusion injury (I/R) only, group II: early RIPC rats (RIPC 2 hours prior to I/R), group III: acriflavine-treated early RIPC rats. Acriflavine is a drug that binds directly to HIF-1 alpha and HIF-2 alpha subunits, thus inhibiting its dimerization and transcriptional activity, and it was injected IP 10 days prior to RIPC. On sacrifice day, ECG was recorded and isolated heart studies were performed. Later, cardiac chambers weight, serum HIF-1-alpha, myocardial perfusate lactate dehydrogenase, and cardiac oxidative markers: Malonaldehyde and glutathione perioxidase were measured. Results Compared to the control group, the early RIPC group showed significant increase in the heart rate (HR), QTc interval in the ECG recording, glutathione peroxidase and the HIF 1α levels together with reduction in the percent of decrease in PT and PT/LV, in the percent of prolongation in time to peak tension (TPT), perfusate lactate dehydrogenase and MDA levels, while no significant changes were recorded in the heart chronotropic activity, in the percent of half relaxation time (HRT) prolongation, or in the percent of decrease of MFR. Following acriflavine treatment, the effects of RIPC were abolished highlighting the role of HIF-1-alpha in mediating RIPC protective effects. Conclusion The non-invasive and non-pharmological remote ischemic preconditioning technique can ameliorate the cardiac ischemic reperfusion injury with an obvious role of HIF-1α in mediating these protective effects.

ERYTHROPOIETIN HAS AN ADDITIVE CYTOPROTECTIVE AND BENEFICIAL EFFECT TO SILDENAFIL IN A MODEL OF DIASTOLIC HEART FAILURE IN RATS

Development of new forms of interventions for diastolic heart failure (HFpEF) remains a challenging task. The aim: Assessing the effect of combining erythropoietin and sildenafil on the left ventricle “LV” functions and morphometry in NG-nitro-L-arginine methyl ester (L-NAME)-induced HFpEF model in rats. Method: Forty-eight female albino rats were randomly assigned to one of six treatment groups: “C” (Control), “L” (L-NAME-treated), “L+M” (L-NAME+milrinone-treated), “L+S” (L-NAME+sildenafil-treated), “L+E” (L-NAME+erythropoietin-treated), and “L+S+E” (L-NAME+sildenafil+erythropoietin-treated). Assessment was done by morphometric examination, LV ejection fraction (LVEF) and fraction of shortening (LVFS)], ECG changes, and mean time to peak tension (TPT) and to complete relaxation (TCR) of isometric contraction of LV muscle strip stimulated by single (TPT-S & TCR-S) and by repeated pulses (TPT-R & TCR-R), respectively. Results: L-NAME resulted in cardiac dysfunction with significant reduction in the mean “LVEF” and “LVFS”, and prolonged both the mean “TPT-R” and “TCR-R”. Milrinone and sildenafil treatment significantly corrected these parameters. In addition, erythropoietin significantly ameliorated “LVEF” and “LVFS” and shortened “TPT-S”. Similarly, “sildenafil+erythropoietin” treatment significantly corrected the measured parameters; however, they were insignificantly different from that of sildenafil only treatment. Morphometrically, sildenafil treatment resulted in significant but partial improvement in L-NAME-induced myocardial injury. Meanwhile, erythropoietin treatment showed more improvement. Moreover, combination treatment showed the best histologic picture in all of the treated groups. Conclusion: Sildenafil was able to improve cardiac functions mainly by accelerating diastolic relaxation. Addition of erythropoietin to sildenafil improved its cytoprotective effect.

The sag response in human muscle contraction.

We examined how muscle length and time between stimuli (inter-pulse interval, IPI) influence declines in force (sag) seen during unfused tetani in the human adductor pollicis muscle. A series of 16-pulse contractions were evoked with IPIs between 1 × and 5 × the twitch time to peak tension (TPT) at large (long muscle length) and small (short muscle length) thumb adduction angles. Unfused tetani were mathematically deconstructed into a series of overlapping twitch contractions to examine why sag exhibits length- and IPI-dependencies. Across all IPIs tested, sag was 62% greater at short than long muscle length, and sag increased as IPI was increased at both muscle lengths. Force attributable to the second stimulus increased as IPI was decreased. Twitch force declined from maximal values across all IPI tested, with the greatest reductions seen at short muscle length and long IPI. At IPI below 2 × TPT, the twitch with highest force occurred earlier than the peak force of the corresponding unfused tetani. Contraction-induced declines in twitch duration (TPT + half relaxation time) were only observed at IPI longer than 1.75 × TPT, and were unaffected by muscle length. Sag is an intrinsic feature of healthy human adductor pollicis muscle. The length-dependence of sag is related to greater diminution of twitch force at short relative to long muscle length. The dependence of sag on IPI is related to IPI-dependent changes in twitch duration and twitch force, and the timing of peak twitch force relative to the peak force of the associated unfused tetanus.

Increase in post activation potentiation in females following a cycling warmup

Post activation potentiation (PAP) is a phenomenon in which muscular force is acutely enhanced as a result of prior contractile activity. The net augmentation is dependent upon the intensity of the preceding conditioning contraction influencing calcium release and phosphorylation of the regulatory myosin light chain. This phenomenon has been recorded after various types of conditioning contractions, however the interaction of a warmup on PAP remains uncertain and whether this differs between males and females requires consideration. We investigated the effect of a cycling warmup on twitch contractile properties and PAP of the plantar flexors on males and in females using oral contraceptives. A maximal voluntary contraction (MVC) of the plantar flexors preceded and followed a 10-min cycling warmup, where supramaximal twitches were administered prior to, during and after the conditioning contractions. Twitch contractile properties of peak tension (PT), time to peak tension (TPT), half relaxation time (HRT) and contraction duration (CD) were compared between resting and potentiated twitches before and after the warmup. Ultrasonography was used to measure in vivo Achilles tendon architecture. Males were ∼30% stronger, but voluntary activation did not differ from females (p = .37). In males and females PT increased following the conditioning MVC (p = .03). The degree of potentiation was higher following the warmup in females (25.01%, p = .02) but not males (p = .24). TPT, HRT and contraction duration (p < .05) were faster after the warmup and in males (p < .001). Achilles tendon elongation was unchanged by the warmup (p = .11). Ten minutes of a cycling warmup reduced TPT, HRT, and CD in both males and females without altering the tendon. The degree of PAP was higher in females than males following the warmup. This difference might be associated with altered calcium kinetics of females on oral contraceptives as well as higher proportion of type I fibres in the active muscles.

Development and evaluation of a removable tissue-engineered muscle with artificial tendons

Tissue-engineered skeletal muscles were potentially useful as physiological and biochemical invitro models. Currently, most of the similar models were constructed without tendons. In this study, we aimed to develop a simple, highly versatile tissue-engineered muscle with artificial tendons, and to evaluate the contractile, histological and molecular dynamics during differentiation. C2C12 cells were embedded in a cold type-І collagen gel and placed between two artificial tendons on a silicone sheet. The construct shrank and tightly attached to the artificial tendons with differentiation, finally detaching from the silicone sheet within 1 week of culture onset. We successfully developed a tissue-engineered skeletal muscle with two artificial tendons from C2C12 myoblasts embedded in type-І collagen gel. The isometric twitch contractile force (TCF) significantly increased during differentiation. Time to Peak Tension (TPT) and Half-Relaxation Time (1/2RT) were significantly shortened during differentiation. Myogenic regulatory factors were maximally expressed at 2 weeks, and subsequently decreased at 3 weeks of culture. Histological analysis indicated that myotube formation increased markedly from 2 weeks and well-ordered sarcomere structures were observed on the surface of the 3D engineered muscle at 3 weeks of culture. These results suggested that robust muscle structure occurred by 3 weeks in the tissue-engineered skeletal muscle. Moreover, during the developmental process, the artificial tendons might contribute to well-ordered sarcomere formation. Our results indicated that this simple culture system could be used to evaluate the effects of various pharmacological and mechanical cues on muscle contractility in a variety of research areas.

Influence of 120-Day Stimulated Microgravity with Countermeasures on Human Muscle Musculo-Tendinous Stiffness and Contractile Properties

The effect of long-term (120-day) 5 ° head-down tilt (HDT) bed rest with countermeasures (physical training - PT) on the contractile properties and musculo-tendinous stiffness (MTS) of the human triceps surae muscle (TS) was studied in four healthy young women subjects. 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. The maximal voluntary contraction (MVC), and isometric twitch contraction (P t ), and electrically evoked tetanic tension at 150 impulses. s -1 (Ро), time-to-peak tension (TPT), and half relaxation time (1/2 RT), and total contraction time (TCT) of the twitch were determined. The difference between Ро and MVC expressed as a percentage of Ро and referred to a force deficiency (FD). The MTS was determined according to the electromechanical delay (EMD) value during the explosive voluntary contraction. Surface electrodes sensed electromyographic activity (EMG) in the soleus muscle. A separate timer was used to determine total reaction time (TRT). Pre-motor time (PMT) was taken to be the time interval from the delivery of the signal to change in EMG. Electromechanical delay (EMD) was the time interval between the change in EMG and movement muscle force production. After HDT with PT the TPT, 1/2 RT and TCT of the TS decreased by 4%, 17%, and 19%, respectively. The МVС, Р t , and Р о decreased by 3% (р>0.05), and 14%, and 9%, respectively. The FD had decreased significantly by 10 % (р<0.02). The rate of increase of electrically evoked tetanic did not change significantly during HDT with PT, but the rate of increase in isometric voluntary tension development was increased. The EMD, PMT, and TRT decreased by 12.2% (p<0.05), 5.3% and 7.3% (p<0.01), respectively. The results obtained demonstrate that PT counteracted the negative effect of mechanical unloading, but the total physical load (mainly its intensity) was obviously insufficient to prevent changes to the mechanical properties of the muscular system, although both a nervous and muscular response to PT was observed.

Contractile and metabolic properties of engineered skeletal muscle derived from slow and fast phenotype mouse muscle.

Satellite cells derived from fast and slow muscles have been shown to adopt contractile and metabolic properties of their parent muscle. Mouse muscle shows less distinctive fiber-type profiles than rat or rabbit muscle. Therefore, in this study we sought to determine whether three-dimensional muscle constructs engineered from slow soleus (SOL) and fast tibialis anterior (TA) from mice would adopt the contractile and metabolic properties of their parent muscle. Time-to-peak tension (TPT) and half-relaxation time (1/2RT) was significantly slower in SOL constructs. In agreement with TPT, TA constructs contained significantly higher levels of fast myosin heavy chain (MHC) and fast troponin C, I, and T isoforms. Fast SERCA protein, both slow and fast calsequestrin isoforms and parvalbumin were found at higher levels in TA constructs. SOL constructs were more fatigue resistant and contained higher levels of the mitochondrial proteins SDH and ATP synthase and the fatty acid transporter CPT-1. SOL constructs contained lower levels of the glycolytic enzyme phosphofructokinase but higher levels of the β-oxidation enzymes LCAD and VLCAD suggesting greater fat oxidation. Despite no changes in PGC-1α protein, SOL constructs contained higher levels of SIRT1 and PRC. TA constructs contained higher levels of the slow-fiber program repressor SOX6 and the six transcriptional complex (STC) proteins Eya1 and Six4 which may underlie the higher in fast-fiber and lower slow-fiber program proteins. Overall, we have found that muscles engineered from predominantly slow and fast mouse muscle retain contractile and metabolic properties of their native muscle.

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

Streptomycin decreases the functional shift to a slow phenotype induced by electrical stimulation in engineered muscle.

Chronic low-frequency stimulation (CLFS) has long been used to induce a fast-to-slow phenotype shift in skeletal muscle. In this study, we explore the role of frequency (10 and 20 Hz), active time (15-60%), and streptomycin in inducing a fast-to-slow shift in engineered muscle. We found that C2C12 engineered muscle could respond to CLFS with an adult-like active time of 60% and found that a constant 10 Hz train of 0.6 s, followed by 0.4 s rest, induced a partial fast-to-slow phenotype shift. Following 2 weeks of CLFS, time-to-peak tension (TPT) (control [CTL]=40.9±0.2 ms; 10 Hz=58.5±3.5 ms; 20 Hz=48.2±2.7 ms) and half-relaxation time (1/2RT) (CTL=50.4±0.6 ms; 10 Hz=76.1±3.3 ms; 20 Hz=66.6±2.3 ms) slowed significantly in frequency, but not in an active time-dependent manner. Streptomycin significantly blunted the slowing of TPT and 1/2RT induced by CLFS by minimizing the fast-to-slow shift in SERCA isoform. Streptomycin (Nonstim=-42.8%±2.5%; Stim=-38.1%±3.6%) significantly prevented the improvement in fatigue resistance seen in CTL constructs (Nonstim=-58.4%±3.6%; Stim=-27.8%±1.7%). Streptomycin reduced the increase seen in GLUT4 protein following CLFS (CTL=89.4%±6.7%; STREP=41.0%±4.3%) and prevented increases in the mitochondrial proteins succinate dehydrogenase (SDH) and ATP synthase. These data demonstrate that streptomycin significantly blunts the fast-to-slow shift induced by CLFS. In the absence of streptomycin, CLFS induced slowing of contractile dynamics and improved fatigue resistance and suggests that this model can be used to study the mechanisms underlying CLFS-induced adaptations in muscle phenotype.

Cardiovascular effects of long-term caffeine administration in aged rats

To evaluate the possible beneficial effect of long-term caffeine administration on cardiovascular system in aged rats. This study was carried out on 20 senile male albino rats, aged 18-20 months. Rats were divided into caffeine-treated group, which received 25 mg/kg caffeine by gavage daily for 6 weeks, and control group. All rats were subjected to the following in vivo measurements: body weight, arterial blood pressure, heart rate and ECG recording. In vitro measurements included studying isolated hearts in a Langendorff apparatus for their intrinsic properties as well as plasma levels of lipids, malondialdehyde and nitrate. Caffeine administration to aged rats significantly enhanced the baseline and maximum values achieved in response to isoproterenol infusion in isolated heart preparation for both maximum rate of tension development (dT/dt max) and time to peak tension (TPT). The responses of hearts isolated from caffeine group to the three doses of isoproterenol infusion also showed a significantly higher dT/dt max with shorter TPT and half relaxation time (1/2 RT) compared to controls. Plasma nitrate was significantly increased and ECG recording was nonsignificantly affected in caffeine group. The plasma levels of total cholesterol, LDL cholesterol as well as in vivo heart rate and systolic, diastolic and mean arterial blood pressures were all significantly increased associated with a significant decrease in HDL cholesterol in caffeine group. Long-term caffeine administration in aged rats increased cardiac inotropy, lusitropy and preserved NO level, which points to a promising potential favorable effect on cardiac intrinsic properties.

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.

Impaired muscle function in a mouse surgical model of osteoarthritis

Impaired muscle function in a mouse surgical model of osteoarthritis

Ligustrazine and the Contractile Properties of Soleus Muscle in Hindlimb-Unloaded Rats

In this study we investigated the effects of different dosages of ligustrazine (tetramethylpyrazine, Tmp) on soleus function and sarco(endo)plasmatic reticulum Ca(2+)-ATPase (SERCA) activity in 14-d hindlimb-unloaded (HU) rats. Female Sprague-Dawley rats were randomly divided into 4 groups (8 rats in each group): synchronous control (CON); HU plus intragastric water instillation (HU-W); HU plus different dosages of instilled Tmp (high: 42.53 mg x kg(-1), HU-TmpH; low: 21.15 mg x kg(-1), HU-TmpL). Muscle contraction force was examined in the soleus muscle. SERCA activity was assayed according to the released inorganic phosphate content. As expected, in HU-W, soleus peak twitch tension (Pt), peak tetanic tension (P0), time to 50% peak tension (TP50), time to peak tension (TPT), time from peak tension to 50% relaxation (RT50), and SERCA activity decreased, all compared with CON. HU-TmpH Pt and P0 values were 179% and 90% above HU-W, and 187% and 124% above HU-W in HU-TmpL, respectively. TP50 and TPT values were 148% and 80% slower than HU-W with HU-TmpH and 95% and 32% in the HU-TmpL group, respectively. RT50 was slower than HU-W by 21% in HU-TmpH; SERCA activity elevated by 56% with HU-TmpH and by 72% with HU-TmpL. Ligustrazine may alleviate the decrease of muscle contractile force and increase of shortening velocity in atrophied soleus, possibly by means of elevated sarcoplasmic reticulum Ca(2+)-ATPase activity.

Cократительные свойства и мышечно-сухожильная жесткость трехглавой мышцы голени и их изменения в результате продолжительного постельного режима

The effect of a 120-day 5 degree head-down tilt (HDT) bed rest on the mechanical properties and electromechanical delay (EMD) of the human triceps surae (TS) muscle was studied in four (mean age 31.5+/-1.7 yr) healthy young women subjects. The TS mechanical properties were evaluated based on the following indicators: maximal voluntary contraction (MVC), maximal strength (Po; frequency 150 Hz), peak twitch force (Poc), time-to-peak tension (TPT), half-relaxation time (1/2 RT) and tension development time to reach 25, 50, 75 and 90% of maximal tension. Force deficit (Pd) were estimated. In response to a light signal,the subject was supposed to make a voluntary foot flexion, with the instruction "to exert the fastest and greatest tension". EMD measurements were recorded from each subject during voluntary contraction. Surface electrodes sensed electromyographic (EMG) activity in the soleus muscle. A separate timer was used to determine total reaction time (TRT). Premotor time (PMT) was taken to be the time interval from the delivery of the signal to change in EMG. EMD was the time interval between the change in EMG and movement i.e. the time interval between EMG and the onset of muscle tension. After HDT Poe, MVC and Po decreased by 24.4, 36.1 and 11.5%, respectively, while Pd increased by 38.8%. TPT increased by 13.6%, while 1/2RT decreased by 19.2%. The rate of increase of voluntary contractions calculated according to a relative scale significantly increased, while the rate of development of electrically evoked contraction did not show any significant differences. The voluntary contraction EMD increased by 27.4%; PMT by 8.7%, and TRT by 13.6%. Thus, the mechanical changes suggest that weightlessness changes not only the peripheral processes associated with contractions but also the central and neural command. EMD is a simple and quick method for evaluation of muscle stiffness changes. Moreover, EMD can serve as an indicator of the functional condition of the neuromuscular system.

Evoked Contractile Properties of the Quadriceps Across a Clinical Spectrum of Knee Osteoarthritis

Evoked contractile properties of whole muscle can provide indirect information about fibre composition and may provide insight into the mechanisms of quadriceps muscle weakness in knee osteoarthritis (OA). PURPOSE: To determine if differences in evoked contractile properties exist across a clinical spectrum of knee OA. METHODS: The following parameters were measured in the knee extensors in thirty-four patients (19 female) with clinical or radiographic knee OA: 1) isometric maximal voluntary torque, 2) resting maximal twitch tension (PT), time-to-peak tension (TPT) and half-relaxation time (HRT), 3) force-frequency characteristics measured with 500 ms pulse trains of 1, 2, 5, 8, 10, 12, 15, 20, 30, 40, 50, 75 and 100 Hz, with stimulus intensity normalized to a value eliciting a torque equivalent to 20% maximal voluntary contraction at 100 Hz. In order to facilitate comparison, participants were stratified into tertiles of disease severity based on their responses to the Western Ontario and McMaster Osteoarthritis Index. The lowest, middle and highest tertiles were designated mild, moderate and severe knee OA, respectively. RESULTS: Maximal isometric strength (normalized to body mass) was significantly lower in the severe (∼45%) and moderate (∼30%) compared to mild subgroup with post-hoc testing (p<0.05). No significant differences were observed across groups for PT, TPT or HRT (p>0.05). Torque values for each subgroup were not significantly different at any of the stimulation frequencies (p>0.05). CONCLUSION: Evoked contractile properties of quadriceps were not different across a clinical spectrum of patients with knee OA, despite differences in isometric knee extensor strength. These results indicate that muscle fibre composition may not be altered in knee OA and other mechanisms may play a greater role in the observed strength losses.

Функциональные свойства нервно-мышечного аппарата человека и их изменения в результате механической разгрузки разной длительности

This study examined the effects of short- (1-, and 3-day) and long-term (7-day) 'dry' immersion (DI) on neuromuscular function of human the triceps surae muscle. The isometric twitch tension (Pt) decreased by 8.7% after 1-days, but increased by 11.5 and 9.8 % after 3- and 7-days DI, respectively. Maximal voluntary contraction (MVC) decreased by 13.6, 19.7, and 33.8% after 1-, 3-, and 7-days DI, respectively (p < 0.05-0.01), electrically evoked (frequency of 150 impulses x s(-1)) tetanic tension (Po) reduced by 1.8, 5.3, and 8.2%, respectively, (nonsignificant). The difference between Po and MVC expressed as a percentage of Po and referred to as force deficiency (Fd) was also calculated. Fd increased by 23.4, 20.2, and 78.7% after 1-, 3-, and 7-days, respectively (p < 0.05-0.001). After DI, the time-to-peak tension (TPT), half-relaxation time (1/ 2 RT), and total contraction time (TCT) was reduced. The TPT decreased by a mean value of 8.5, and 3.3% after 1- and 3-days, respectively, and after 7-day did not reveal significant changes in the curve of the TPT. 1/2 RT and TCT was shorter in the post-immersion condition than in the control value. The rate of increase of voluntary contraction calculated according to relative scale was significantly reduced after DI (p < 0.05-0.001), but for the electrically evoked contraction (frequency of 150 impulses x s(-1)) there were no substantial changes from the initial physiological state. A standard 2-min fatigue of electrically-induced intermittent test (frequency of 50 impulses x s(-1)) did not differ substantially from the initial physiological state, but the electrical M-waves reduced significantly. The relative extent of the decline in either of these two parameters can be determined from the change in the relation of the electrical M-wave to the contractile response (the E/C ratio). After long-term DI (7 day) of muscle a significantly greater decline of electrical waves is observed as compared to contractile response by a short-term DI (1-, and 3-day), respectively.

Static Stretch Training in Conditions of Simulated Microgravity Maintains Contractile Properties of Muscles?

The effect of a 60-day 6° head-down tilt (HDT) of bed rest with and without countermeasures on the mechanical properties of human the triceps surae muscle was studied in 12 healthy young men subjects. One group (n = 6; mean age (30.8 ± 3.1) years) underwent a 60-day HDT and a second group (n = 6; mean age (30.5 ± 1.9) years) underwent HDT with countermeasures (long-term passive stretching). The results shown that the contractile properties of skeletal muscle change considerably. After HDT without countermeasures the maximal voluntary contraction (MVC) declined by 33.5% (p < 0.05), the electrically evoked tetanic tension at 150 Hz (P0) and isometric twitch contraction (Pt) reduced by 18.0% (p < 0.02) and 17.3% (p < 0.05), respectively. Time-to-peak tension (TPT) of the twitch increased by 3.4%, but half-relaxation time (1/2 RT) decreased by 7.2%, and total contraction time (TCT) not significantly increased. The difference between P0 and MVC expressed as a percentage of P0 and referred to as force deficiency (Pd), has also been calculated. The Pd increased by 61% (p < 0.001). The rate of rise of voluntary contractions calculated according to an relative scale significantly reduced, but the electrically evoked contraction no substantial changes were observed. After HDT with long-term passive stretching caused decrease by 43.0% (p < 0.05) in MVC, and Pt, and in P0 by 17.0%, and by 19.4% (p < 0.05), respectively. The Pd increased significantly by 100% (p < 0.001). TPT, and 1/2 RT not change significantly, and TCT of the twitch increased by 6.5%, respectively in relation to the control condition. The rate of rise of electrically evoked tetanic tension did not change significantly during HDT with countermeasures but the rate of rise in on isometric voluntary tension development were decreased. These data indicate that prolonged passive stretching of a single muscle decreases voluntary strength. Thus, the received data specify, that the long passive stretching of a muscle does not find out preventive facilitate contractile properties of the muscular device from negative influences of mechanical unloading. This study presents evidence that prolonged passive muscle stretching can lead to some modification of contraction material behavior. In addition, altered material properties seem to affect proprioceptive feedback and, therefore, the motor unit activation in proportion to the contractile failure.