Tetanic Tension Research Articles

Do bupivacaine, clindamycin, and gentamicin at their clinical concentrations enhance rocuronium-induced neuromuscular block?

BackgroundBupivacaine, clindamycin, and gentamicin inhibit neuromuscular (NM) conduction. When they are combined, they may synergistically reduce the effective concentration of each to the therapeutic concentration in augmenting rocuronium-induced NM block. Thus, the aim of this study was to investigate whether combinations of the three drugs, at around their therapeutic concentrations, potentiate rocuronium-induced NM block.MethodsFifty-seven left-phrenic nerve hemidiaphragms (Male S-D rats, 150-250 g) were hung in a 20-ml organ bath filled with Krebs solution. Three consecutive single-twitch tensions (0.1 Hz) and one tetanic tension (50 Hz for 1.9 s) were obtained. A Krebs solution was premixed with concentration sets of bupivacaine and clindamycin, bupivacaine and gentamicin, or bupivacaine, clindamycin and gentamicin. Then, the concentration of rocuronium was cumulatively increased in the Krebs solution (1, 3, 5, 7, 9, 12, 14, 16, 18, and 20 µM) until an 80% to 90% reduction in single twitch was attained. The effective concentrations for each experiment were determined with the probit model.ResultsThe combinations of bupivacaine, clindamycin, and gentamicin enhanced rocuronium-induced NM block. When the three drugs were applied simultaneously, their concentrations were reduced to near-therapeutic levels in potentiating the action of rocuronium.ConclusionsBupivacaine, clindamycin, and gentamicin blocked NM conduction, and when all three drugs were applied together, they augmented rocuronium-induced NM block at their near-therapeutic concentrations. Clinicians should be aware of the cooperability in NM block between drugs that interrupt NM conduction.

Differential effects of targeted tongue exercise and treadmill running on aging tongue muscle structure and contractile properties

Age-associated changes in tongue muscle structure and strength may contribute to dysphagia in elderly people. Tongue exercise is a current treatment option. We hypothesized that targeted tongue exercise and nontargeted exercise that activates tongue muscles as a consequence of increased respiratory drive, such as treadmill running, are associated with different patterns of tongue muscle contraction and genioglossus (GG) muscle biochemistry. Thirty-one young adult, 34 middle-aged, and 37 old Fischer 344/Brown Norway rats received either targeted tongue exercise, treadmill running, or no exercise (5 days/wk for 8 wk). Protrusive tongue muscle contractile properties and myosin heavy chain (MHC) composition in the GG were examined at the end of 8 wk across groups. Significant age effects were found for maximal twitch and tetanic tension (greatest in young adult rats), MHCIIb (highest proportion in young adult rats), MHCIIx (highest proportion in middle-aged and old rats), and MHCI (highest proportion in old rats). The targeted tongue exercise group had the greatest maximal twitch tension and the highest proportion of MHCI. The treadmill running group had the shortest half-decay time, the lowest proportion of MHCIIa, and the highest proportion of MHCIIb. Fatigue was significantly less in the young adult treadmill running group and the old targeted tongue exercise group than in other groups. Thus, tongue muscle structure and contractile properties were affected by both targeted tongue exercise and treadmill running, but in different ways. Studies geared toward optimizing dose and manner of providing targeted and generalized tongue exercise may lead to alternative tongue exercise delivery strategies.

Tongue muscle plasticity following hypoglossal nerve stimulation in aged rats

Age-related decreases in tongue muscle mass and strength have been reported. It may be possible to prevent age-related tongue muscle changes using neuromuscular electrical stimulation (NMES). Our hypothesis was that alterations in muscle contractile properties and myosin heavy chain composition would be found after NMES. Fifty-four young, middle-aged, and old 344/Brown Norway rats were included in this study. Twenty-four rats underwent bilateral electrical stimulation of the hypoglossal nerves for 8 weeks and were compared with control or sham rats. Muscle contractile properties and myosin heavy chain (MHC) in the genioglossus (GG), styloglossus (SG), and hyoglossus (HG) muscles were examined. Compared with unstimulated control rats, we found reduced muscle fatigue, increased contraction and half-decay times, and increased twitch and tetanic tension. Increased type I MHC was found, except for in GG in old and middle-aged rats. Transitions in tongue muscle contractile properties and phenotype were found after NMES.

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.

Loss of muscle strength during sepsis is in part regulated by glucocorticoids and is associated with reduced muscle fiber stiffness

Sepsis is associated with impaired muscle function but the role of glucocorticoids in sepsis-induced muscle weakness is not known. We tested the role of glucocorticoids in sepsis-induced muscle weakness by treating septic rats with the glucocorticoid receptor antagonist RU38486. In addition, normal rats were treated with dexamethasone to further examine the role of glucocorticoids in the regulation of muscle strength. Sepsis was induced in rats by cecal ligation and puncture, and muscle force generation (peak twitch and tetanic tension) was determined in lower extremity muscles. In other experiments, absolute and specific force as well as stiffness (reflecting the function of actomyosin cross bridges) were determined in isolated skinned muscle fibers from control and septic rats. Sepsis and treatment with dexamethasone resulted in reduced maximal twitch and tetanic force in intact isolated extensor digitorum longus muscles. The absolute and specific maximal force in isolated muscle fibers was reduced during sepsis together with decreased fiber stiffness. These effects of sepsis were blunted (but not abolished) by RU38486. The results suggest that muscle weakness during sepsis is at least in part regulated by glucocorticoids and reflects loss of contractility at the cellular (individual muscle fiber) level. In addition, the results suggest that reduced function of the cross bridges between actin and myosin (documented as reduced muscle fiber stiffness) may be involved in sepsis-induced muscle weakness. An increased understanding of mechanisms involved in loss of muscle strength will be important for the development of new treatment strategies in patients with this debilitating consequence of sepsis.

Effect of Shengmai injection (生脉注射液) on diaphragmatic contractility in doxorubicin-treated rats

To explore the diaphragmatic toxicity in doxorubicin (DOX)-treated rats and the related mechanisms, as well as the effects of Shengmai Injection (SMI, ) on the diaphragmatic dysfunction. Thirty Sprague-Dawley male rats were randomly divided into three groups: control, DOX-treated and DOX+SMI treated groups. DOX was given to rats in DOX and DOX+SMI groups in 6 equal doses [2.5 mg/kg, intraperitoneal injection (i.p.)], on alternate days, over a period of 2 weeks for a cumulative dose of 15 mg/kg. SMI was given to DOX+SMI rats in 12 doses (3 mL/kg, i.p.) for a period of 2 weeks before the administration of DOX and 2 weeks during the administration of DOX. The rats in the control group received equal volume of normal saline. Subsequently, the twitch and tetanic characteristics and force-frequency relationships, and the malondialdehyde (MDA) levels and the superoxide dismutase (SOD) activities, as well as the mRNA content and proteins of inducible nitric oxide synthase (iNOS) were determined. The DOX-treated rats had decreased the peak twitch tension (Pt), maximal tetanic tension (P0) and force-frequency relationship as compared with the control rats (P<0.01), while the diaphragm contractility in rats treated with SMI were significantly higher than that in DOX-treated rats (P<0.01). The DOX-treated rats had increased MAD levels and decreased SOD activities (P<0.05), and SMI decreased the MDA levels and increased the SOD activities in DOX-treated rats (P<0.05). Ultrastructure of diaphragm in the DOX-treated rats revealed typical alterations including fracture of diaphragm fibers, and edema and degeneration of mitochondria; these changes were relieved by SMI treatment. The mRNA content and protein of iNOS in DOX-treated rats were remarkably higher than those in control rats (P<0.01), while SMI decreased the mRNA expression level of iNOS in DOX-treated rats (P<0.05). Lipid peroxidation is responsible for DOX-induced diaphragm toxicity. SMI protects diaphragm muscles and their function from DOX impairment, and these beneficial effects may be somehow correlated with the decrease in expression of iNOS and lipid peroxidation.

Tension cost correlates with mechanical and biochemical parameters in different myocardial contractility conditions

OBJECTIVES:Tension cost, the ratio of myosin ATPase activity to tension, reflects the economy of tension development in the myocardium. To evaluate the mechanical advantage represented by the tension cost, we studied papillary muscle contractility and the activity of myosin ATPase in the left ventricles in normal and pathophysiological conditions.METHODS:Experimental protocols were performed using rat left ventricles from: (1) streptozotocin-induced diabetic and control Wistar rats; (2) N-nitro-L-arginine methyl ester (L-NAME) hypertensive and untreated Wistar rats; (3) deoxycorticosterone acetate (DOCA) salt-treated, nephrectomized and salt- and DOCA-treated rats; (4) spontaneous hypertensive rats (SHR) and Wistar Kyoto (WKY) rats; (5) rats with myocardial infarction and sham-operated rats. The isometric force, tetanic tension, and the activity of myosin ATPase were measured.RESULTS:The results obtained from infarcted, diabetic, and deoxycorticosterone acetate-salt-treated rats showed reductions in twitch and tetanic tension compared to the control and sham-operated groups. Twitch and tetanic tension increased in the N-nitro-L-arginine methyl ester-treated rats compared with the Wistar rats. Myosin ATPase activity was depressed in the infarcted, diabetic, and deoxycorticosterone acetate salt-treated rats compared with control and sham-operated rats and was increased in N-nitro-L-arginine methyl ester-treated rats. These parameters did not differ between SHR and WKY rats. In the studied conditions (e.g., post-myocardial infarction, deoxycorticosterone acetate salt-induced hypertension, chronic N-nitro-L-arginine methyl ester treatment, and streptozotocin-induced diabetes), a positive correlation between force or plateau tetanic tension and myosin ATPase activity was observed.CONCLUSION:Our results suggest that the myocardium adapts to force generation by increasing or reducing the tension cost to maintain myocardial contractility with a better mechanical advantage.

Muscle excursion does not correlate with increased serial sarcomere number after muscle adaptation to stretched tendon transfer

Chronic skeletal muscle stretch typically increases serial muscle fiber sarcomere number. Since serial sarcomere number correlates with functional excursion in normal muscle, observed changes in sarcomere number are often extrapolated to their new assumed function. However, this has not been well demonstrated experimentally. Thus, we measured the functional properties of muscles stretched due to tendon transfer surgery. Muscle active and passive length-tension curves were measured 1 week and 4 weeks after surgery, and then each muscle was further examined to determine structural adaptation as well as single fiber and fiber bundle passive mechanical properties. We found a disconnect between the functional and structural muscle properties. Specifically, muscle excursion was significantly lower in the transferred muscle compared to controls, even though serial sarcomere number had increased. Furthermore, maximum tetanic tension was significantly reduced, though the two groups had similar physiological cross sectional areas. Passive tension increased in the transferred muscle, which was deemed to be due to proliferation of extracellular matrix. These data are the first to report that muscle morphological adaptation after chronic stretch does not accurately predict the muscle's functional properties. These data have significant implications for examining muscle physiological properties under surgical interventions.

Levo-carnitine supplementation normalizes skeletal muscle functions in type 2 diabetic rats

Levo-carnitine is known to improve skeletal muscle contractile functions in healthy humans and rats. It has also been claimed to correct metabolic derangements in type 2 diabetes mellitus (T2DM). This randomized control trial was designed to determine the effect of levo-carnitine on isometric contraction, force frequency relationship and fatigue of skeletal muscles along with oxidative stress in T2DM. Sprague-dawley rats (n=90) were randomly divided in three equal groups. Control group remained healthy while T2DM was induced in the diabetic and carnitine groups. Then, carnitine group was administered levo-carnitine 200mg/kg/day intraperitonealy for 6 days. At 28th day, extensor digitorum longus (EDL) 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) levels. Regarding muscle parameters, no significant difference was found in maximum isometric twitch tension, time-to-peak twitch tension and time-to-relax to 50% of the peak twitch tension amongst the three groups. However, 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 when compared with diabetic group. Serum MDA levels were reduced in carnitine group as compared to the diabetic group. These findings suggest that levo-carnitine supplementation reduces oxidative stress, improves work capacity and delays fatigue in T2DM.

Effects of selenium supplementation on the muscle contractile properties, fatigue and antioxidant enzymes activities of gastrocnemius muscles in trained and untrained rats

Selenium (Se) is an important component of cellular seleno ‐compounds andan integral component of glutathione Peroxidase (GPx), which catalyzes thereduction of harmful radicals produced during muscular exercise. The currentstudy was carried out to evaluate the muscle contractile properties andfatigue resistance of gastrocnemius muscle under selenium supplementationschemes in sedentary and exercise protocols as well as measure the antioxidantenzymes activity and lipid peroxidation. Rats were divided into fourgroups; sedentary Selenium supplementation (S), exercise Selenium (SE)groups, sedentary control (SC) and exercise control (EC) groups. The ratswere fed with 80 μg/kg body weights selenium for six weeks. The exerciseprotocol consisted the 40 jumps up to the height of 40 cm for 6 ‐week. Themuscle fatigue protocol consisted the trains of pulses of 40 Hz at every secondfor at least 2 min. Significant (P&lt;0.05) increase was observed in treatedgroups than control in the muscle contractile properties like twitch tension(Pt), contraction time (CT) and twitch/tetanic tension Ratio (Pt/Po Ratio),tetanic tension (Po) and EMG amplitude. Decreased EMG failure and increasedfatigue index were observed in ES group. Moreover, a significant(P&lt;0.05) increase and decrease in the GPx activity and lipid peroxidation respectivelywas also reported than SC and EC group. While there were nochanges reported in the activity of CAT and SOD enzymes. This study revealedthat the Se with jumping exercise induces muscle contractile propertiesand decreases the muscular fatigue.

Genistein attenuates genioglossus muscle fatigue under chronic intermittent hypoxia by down‐regulation of oxidative stress level and up‐regulation of antioxidant enzyme activity through ERK1/2 signaling pathway

This study aims to investigate the effects of genistein on contractile properties of genioglossus under chronic intermittent hypoxia (CIH) conditions and its relationship with oxidative stress, antioxidant enzyme, and ERK1/2 signaling pathway. Fifty female Sprague-Dawley rats were randomly divided into five groups 1 week after ovariectomy: the normal control group, the CIH group, the CIH with low-dose, medium-dose, and high-dose genistein groups. Rats in the latter four groups were exposed to CIH for 5 weeks. Twitch tension, tetanic tension, and fatigue resistance of genioglossus were investigated. Malondialdehyde (MDA) and mitochondrial reactive oxygen species (ROS), enzymatic activity of superoxide dismutase (SOD), glutathione peroxidase (GPx), catalase (CAT), and ERK1/2 were detected. Muscle fatigue resistance and enzymatic activity of GPx, CAT, and SOD were reduced after CIH exposure and improved by different doses of genistein at different degrees. CIH increased the level of ROS and MDA, and they were returned to normal by genistein. The expression of phospho-ERK1/2 is opposite to the changes in muscle fatigue resistance. Chronic intermittent hypoxia decreases fatigue resistance of genioglossus, and genistein treatment reverses the fatigability of genioglossus by down-regulation of oxidative stress level and up-regulation of antioxidant enzymatic activity probably through ERK1/2 signaling pathway.

Role of acetylcholinesterase on the structure and function of cholinergic synapses: insights gained from studies on knockout mice.

Electrophysiological and ultrastructural studies were performed on phrenic nerve-hemidiaphragm preparations isolated from wild-type and acetylcholinesterase (AChE) knockout (KO) mice to determine the compensatory mechanisms manifested by the neuromuscular junction to excess acetylcholine (ACh). The diaphragm was selected since it is the primary muscle of respiration, and it must adapt to allow for survival of the organism in the absence of AChE. Nerve-elicited muscle contractions, miniature endplate potentials (MEPPs) and evoked endplate potentials (EPPs) were recorded by conventional electrophysiological techniques from phrenic nerve-hemidiaphragm preparations isolated from 1.5- to 2-month-old wild-type (AChE(+/+)) or AChE KO (AChE(-/-)) mice. These recordings were chosen to provide a comprehensive assessment of functional alterations of the diaphragm muscle resulting from the absence of AChE. Tension measurements from AChE(-/-) mice revealed that the amplitude of twitch tensions was potentiated, but tetanic tensions underwent a use-dependent decline at frequencies below 70 Hz and above 100 Hz. MEPPs recorded from hemidiaphragms of AChE(-/-) mice showed a reduction in frequency and a prolongation in decay (37%) but no change in amplitude compared to values observed in age-matched wild-type littermates. In contrast, MEPPs recorded from hemidiaphragms of wild-type mice that were exposed for 30 min to the selective AChE inhibitor 5-bis(4-allyldimethyl-ammoniumphenyl)pentane-3-one (BW284C51) exhibited a pronounced increase in amplitude (42%) and a more marked prolongation in decay (76%). The difference between MEPP amplitudes and decays in AChE(-/-) hemidiaphragms and in wild-type hemidiaphragms treated with BW284C51 represents effective adaptation by the former to a high ACh environment. Electron microscopic examination revealed that diaphragm muscles of AChE(-/-) mice had smaller nerve terminals and diminished pre- and post-synaptic surface contacts relative to neuromuscular junctions of AChE(+/+) mice. The morphological changes are suggested to account, in part, for the ability of muscle from AChE(-/-) mice to function in the complete absence of AChE.

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.

Association of muscle hardness with muscle tension dynamics: a physiological property

This study aimed to investigate the relationship between muscle hardness and muscle tension in terms of length-tension relationship. A frog gastrocnemius muscle sample was horizontally mounted on the base plate inside a chamber and was stretched from 100 to 150% of the pre-length, in 5% increments. After each step of muscle lengthening, electrical field stimulation for induction of tetanus was applied using platinum-plate electrodes positioned on either side of the muscle submerged in Ringer's solution. The measurement of muscle hardness, i.e., applying perpendicular distortion, was performed whilst maintaining the plateau of passive and tetanic tension. The relationship between normalised tension and normalised muscle hardness was evaluated. The length-hardness diagram could be created from the modification with the length-tension diagram. It is noteworthy that muscle hardness was proportional to passive and total tension. Regression analysis revealed a significant correlation between muscle hardness and passive and total tension, with a significant positive slope (passive tension: r = 0.986, P < 0.001; total tension: r = 0.856, P < 0.001). In conclusion, our results suggest that muscle hardness depends on muscle tension in most ranges of muscle length in the length-tension diagram.

A rehabilitation exercise program to remediate skeletal muscle atrophy in an estrogen-deficient organism may be ineffective

To determine rehabilitation exercise program effects under hormone deficient (ovariectomy or OVX) and hormone supplemented [OVX + 17-beta estradiol (E2)] conditions. Mature female rats (n = 123) were assigned to OVX or OVX + E2-supplemented groups. OVX and OVX + E2 groups were allocated to one of four conditions: (1) control, (2) hindlimb unweighted (HLU) for 4 weeks to induce muscle atrophy, (3) cage Recovery for 2 weeks after HLU, and (4) Recovery with 2 weeks of rehabilitation exercise program after 4 weeks of HLU. Atrophy following HLU was comparable for OVX and OVX + E2-supplemented rats and was significant in all muscles examined (soleus, tibialis anterior, plantaris, gastrocnemius, quadriceps). Also significant with HLU was the decline in muscle force (P < 0.05) in soleus, plantaris, gastrocnemius and tibialis anterior (quadriceps not tested). There were trends toward return of muscle mass in Recovery OVX and Recovery OVX + E2 groups but only the E2 supplemented OVX rats had return of muscle mass (4/5 muscles studied) with exercise. Peak tetanic tension (Po) returned to control values in the E2 supplemented Exercise rats but not in the unsupplemented Exercise group. For example, gastrocnemius Po for OVX HLU, OVX Recovery and OVX-Exercise groups was 82%*, 82%* and 76%* of control. Gastrocnemius Po for E2 supplemented HLU, Recovery and Exercise groups was 72%*, 95% and 106% of control (*P < 0.05 compared to control). H&E cross-sections from OVX-Exercise rats showed central nuclei. In conclusion, a rehabilitation exercise program to remediate acute atrophy in females appears more effective if E2 is present.

The reversal by pyridostigmine of neuromuscular block produced by soman.

The effect of pyridostigmine on neuromuscular block produced by soman was studied in the isolated phrenic nerve-diaphragm preparation. In the rat, soman produced an irreversible reduction in tetanic tension and functional acetylcholinesterase (AChE) activity. Pretreatment with pyridostigmine before exposure of the diaphragm to soman, followed by removal of the anticholinesterase from the organ bath, produced a return of tetanic tension and an increase of 5% in functional AChE activity. Similar results were obtained in the guinea-pig. The changes in synaptic AChE activity were verified pharmacologically by showing a decrease in the blocking activity of acetylcholine in preparations pretreated with pyridostigmine in comparison to those given soman alone following removal of the anti-cholinesterase. The blocking dose of carbachol did not change in these two groups indicating that desensitization was not a component of the protective action. A comparison was also made of the results obtained by measuring inhibition of AChE in situ with those obtained from muscle homogenates. The implications of these results are discussed.

Melatonin improves muscle function of the dystrophic mdx5Cv mouse, a model for Duchenne muscular dystrophy

Duchenne muscular dystrophy (DMD) is a severe X-linked muscle-wasting disease caused by the absence of the cytoskeletal protein dystrophin. In addition to abnormal calcium handling, numerous studies point to a crucial role of oxidative stress in the pathogenesis of the disease. Considering the impressive results provided by antioxidants on dystrophic muscle structure and function, we investigated whether melatonin can protect the mdx(5Cv) mouse, an animal model for DMD. Male mdx(5Cv) mouse pups were treated with melatonin by daily intraperitoneal (i.p.) injection (30 mg/kg body weight) or by subcutaneous (s.c.) implant(s) (18 or 54 mg melatonin as Melovine® implants) from 17/18 to 28/29 days of age. Isometric force of the triceps surae was recorded at the end of the treatment. The i.p. treatment increased the phasic twitch tension of mdx(5Cv) mice. The maximal tetanic tension was ameliorated by 18 mg s.c. and 30 mg/kg i.p. treatments. Melatonin caused the dystrophic muscle to contract and relax faster. The force-frequency relationship of melatonin-treated dystrophic mice was shifted to the right. In accordance with improved muscle function, melatonin decreased plasma creatine kinase activity, a marker for muscle injury. Melatonin treatment increased total glutathione content and lowered the oxidized/reduced glutathione ratio, indicating a better redox status of the muscle. In light of the present investigation, the therapeutic potential of melatonin should be further considered for patients with DMD.

Muscles Underlying the Elevation of the Hyolaryngeal Complex

IntroductionA critical event in the pharyngeal phase of swallowing is the elevation of the hyolaryngeal complex opening the upper esophageal sphincter. Current swallowing theory assigns this function to the suprahyoid (mylohyoid, geniohyoid, digastrics, and stylohyoid) and thyrohyoid muscles. The role of the long pharyngeal muscles (stylopharyngeus, palatopharyngeus, and salpingopharyngeus) that insert into the thyroid cartilage and distal pharynx is uninvestigated in humans. This study uses a cadaver model to document the structural properties of muscles to analyze their potential for elevating the hyolaryngeal complex.MethodsMeasurements to determine physiological cross‐sectional areas (PCSAs) of suprahyoid, thyrohyoid and long pharyngeal muscles were taken from hemisected head and neck formalin‐fixed cadaver specimens (n = 14). Coordinates of muscle attachment sites and PCSAs were used to calculate unit force vectors representing the relative maximum tetanic tension muscles in the superior direction. Force vectors of muscle samples were compared by an analysis of variance to evaluate their potential for force in elevating the hyolaryngeal complex.ResultsAn ANOVA with Tukey HSD post hoc analysis of unit force vectors in the superior direction showed the following results: suprahyoid (1.54±0.34 cm2) &gt; long pharyngeal (.74±0.20 cm2) (p&lt;.01), and long pharyngeal &gt; thyrohyoid (.49±0.17 cm2) (p&lt;.05).DiscussionThe morphology of these muscles suggests that while the suprahyoid muscles have the most potential for force in elevating the hyolaryngeal complex, the long pharyngeal muscles contribute significantly more to UES opening than the thyrohyoid. If verified by physiological data, this data would add to the current understanding of swallowing.Grant Funding Source: n/a

Thick-Filament Strain and Interfilament Spacing in Passive Muscle: Effect of Titin-Based Passive Tension

We studied the effect of titin-based passive tension on sarcomere structure by simultaneously measuring passive tension and low-angle x-ray diffraction patterns on passive fiber bundles from rabbit skinned psoas muscle. We used a stretch-hold-release protocol with measurement of x-ray diffraction patterns at various passive tension levels during the hold phase before and after passive stress relaxation. Measurements were performed in relaxing solution without and with dextran T-500 to compress the lattice toward physiological levels. The myofilament lattice spacing was measured in the A-band ( d 1,0) and Z-disk ( d Z) regions of the sarcomere. The axial spacing of the thick-filament backbone was determined from the sixth myosin meridional reflection (M6) and the equilibrium positions of myosin heads from the fourth myosin layer line peak position and the I 1,1/I 1,0 intensity ratio. Total passive tension was measured during the x-ray experiments, and a differential extraction technique was used to determine the relations between collagen- and titin-based passive tension and sarcomere length. Within the employed range of sarcomere lengths (∼2.2–3.4 μm), titin accounted for >80% of passive tension. X-ray results indicate that titin compresses both the A-band and Z-disk lattice spacing with viscoelastic behavior when fibers are swollen after skinning, and elastic behavior when the lattice is reduced with dextran. Titin also increases the axial thick-filament spacing, M6, in an elastic manner in both the presence and absence of dextran. No changes were detected in either I 1,1/I 1,0 or the position of peaks on the fourth myosin layer line during passive stress relaxation. Passive tension and M6 measurements were converted to thick-filament compliance, yielding a value of ∼85 m/N, which is several-fold larger than the thick-filament compliance determined by others during the tetanic tension plateau of activated intact muscle. This difference can be explained by the fact that thick filaments are more compliant at low tension (passive muscle) than at high tension (tetanic tension). The implications of our findings are discussed.

Presynaptic facilitatory adenosine A2A receptors mediate fade induced by neuromuscular relaxants that exhibit anticholinesterase activity

1. Pancuronium, cisatracurium and vecuronium are antinicotinic agents that, in contrast with d-tubocurarine and hexamethonium, exhibit anticholinesterase activity. Pancuronium-, cisatracurium- and vecuronium-induced fade results from blockade of facilitatory nicotinic receptors on motor nerves, but fade produced by such agents also depends on the presynaptic activation of inhibitory muscarinic M2 receptors by acetylcholine released from motor nerve terminals and activation of inhibitory adenosine A1 receptors by adenosine released from motor nerves and muscles. The participation of presynaptic facilitatory A2A receptors in fade caused by pancuronium, cisatracurium and vecuronium has not yet been investigated. In the present study, we determined the effects of ZM241385, an antagonist of presynaptic facilitatory A2A receptors, on fade produced by these neuromuscular relaxants in the rat phrenic nerve-diaphragm (PND) preparation. 2. The muscles were stimulated indirectly at 75±3Hz to induce a sustained tetanizing muscular contraction. The lowest concentration at which each antinicotinic agent produced fade without modifying initial tetanic tension (presynaptic action) was determined. 3. d-Tubocurarine-induced fade occurred only at 55 nmol/L, a concentration that also reduced maximal tetanic tension (post-synaptic action). At 10 nmol/L, ZM 241385 alone did not produce fade, but it did attenuate pancuronium (0.32 μmol/L)-, cisatracurium (0.32 μmol/L)- and vecuronium (0.36 μmol/L)-induced fade. 4. The fade induced by the 'pure' antinicotinic agents d-tubocurarine (55 nmol/L) and hexamethonium (413 μmol/L) was not altered by 10 nmol/L ZM 241385, indicating that presynaptic adenosine A2A receptors play a significant role in the fade produced by antinicotinic agents when such agents have anticholinesterase activity.