Effect of inhibitors of arachidonic acid metabolism on efflux of intracellular enzymes from skeletal muscle following experimental damage

Sternocleidomastoid size and upper trapezius muscle thickness in congenital torticollis patients: A retrospective observational study

The purpose of this study was to investigate the upper trapezius muscle thickness (UTMT) in congenital muscular torticollis (CMT) patients and determine the correlation among sternocleidomastoid muscle thickness (SCMT), accessory nerve (AN) cross-sectional area (CSA), and UTMT in CMT.This retrospective study consisted of 2 participant groups: Group 1 (SCM mass CMT, n = 20) and Group 2 (Postural CMT, n = 22). For both groups, B-mode ultrasound was performed by a physiatrist to measure the SCMT and UTMT and calculate the CSA of the AN. The correlation among SCMT, CSA of the AN, and UTMT in both groups was evaluated.The between-group comparison revealed that Group 1 had significantly greater SCMT, UTMT, and CSA of the AN on the affected side than Group 2 (P < .05). The intragroup comparison between the affected and unaffected sides also revealed that, in Group 1, the SCMT, UTMT, and CSA of the AN were significantly higher on the affected side than on the unaffected side (P < .05), whereas no significant differences were observed in Group 2. In Group 1, a positive correlation (r = 0.55) was observed between the UTMT and CSA of the AN on the affected side, but not observed between the SCMT and CSA of the AN.The findings of the study indicate that sternocleidomastoid muscle size may impact the thickness of the upper trapezius muscle via the accessory nerve in patients with congenital torticollis.

Myostatin dysfunction impairs force generation in extensor digitorum longus muscle and increases exercise-induced protein efflux from extensor digitorum longus and soleus muscles

Myostatin dysfunction promotes muscle hypertrophy, which can complicate assessment of muscle properties. We examined force generating capacity and creatine kinase (CK) efflux from skeletal muscles of young mice before they reach adult body and muscle size. Isolated soleus (SOL) and extensor digitorum longus (EDL) muscles of Berlin high (BEH) mice with dysfunctional myostatin, i.e., homozygous for inactivating myostatin mutation, and with a wild-type myostatin (BEH+/+) were studied. The muscles of BEH mice showed faster (P < 0.01) twitch and tetanus contraction times compared with BEH+/+ mice, but only EDL displayed lower (P < 0.05) specific force. SOL and EDL of age-matched but not younger BEH mice showed greater exercise-induced CK efflux compared with BEH+/+ mice. In summary, myostatin dysfunction leads to impairment in muscle force generating capacity in EDL and increases susceptibility of SOL and EDL to protein loss after exercise.

Efflux of creatine kinase from isolated soleus muscle depends on age, sex and type of exercise in mice

Elevated plasma creatine kinase (CK) activity is often used as an indicator of exercise-induced muscle damage. Our aim was to study effects of contraction type, sex and age on CK efflux from isolated skeletal muscles of mice. The soleus muscle (SOL) of adult (7.5-month old) female C57BL/6J mice was subjected to either 100 passive stretches, isometric contractions or eccentric contractions, and muscle CK efflux was assessed after two-hour incubation in vitro. SOL of young (3-month old) male and female mice was studied after 100 eccentric contractions. For adult females, muscle CK efflux was larger (p < 0.05) after eccentric contractions than after incubation without exercise (698 ± 344 vs. 268 ± 184 mU·h(-1), respectively), but smaller (p < 0.05) than for young females after the same type of exercise (1069 ± 341 mU·h(-1)). Eccentric exercise-induced CK efflux was larger in muscles of young males compared to young females (2046 ± 317 vs 1069 ± 341 mU · h(-1), respectively, p < 0.001). Our results show that eccentric contractions induce a significant increase in muscle CK efflux immediately after exercise. Isolated muscle resistance to exercise-induced CK efflux depends on age and sex of mice. Key pointsMuscle lengthening contractions induce the highest CK efflux in vitro compared with similar protocol of isometric contractions or passive stretches.Muscle CK efflux in vitro is applicable in studying changes of sarcolemma permeability/integrity, a proxy of muscle damage, in response to muscle contractile activity.Isolated muscle resistance to exercise-induced CK efflux is greater in female compared to male mice of young age and is further increased in adult female mice.

Regenerated soleus muscle shows reduced creatine kinase efflux after contractile activity in vitro

Regenerated skeletal muscles show less muscle damage after strenuous muscle exercise. The aim of the studies was to investigate if the regeneration is associated with reduced muscle creatine kinase (CK) efflux immediately after the exercise. Cryolesion was applied to the soleus muscle of 3-month-old C57BL/6J male mice. Then total CK efflux was assessed in vitro in the regenerated muscles without exercise or after 100 eccentric contractions. The same measurements were performed in the control muscles, which were not exposed to cryolesion. Regenerated muscles generated weaker (P < 0.05) twitches, but stronger (P < 0.05) 150-Hz and 300-Hz tetani with prolonged (P < 0.01) contraction times compared with the control muscles. There was no difference between regenerated and control muscles in the total CK efflux without exercise, but only control muscles showed an increase (P < 0.001) in the CK efflux after the exercise. Our results suggest that muscle regeneration is associated with modulation of contractile properties and improvement in muscle resistance to damage after eccentric exercise.

Diagnostic value of real-time sonoelastography in congenital muscular torticollis

OBJECTIVES

The purpose of this study was to evaluate the possible use of real-time sonoelastography in infants with congenital muscular torticollis for predicting treatment outcomes.

METHODS

The study included 20 infants with a sternocleidomastoid muscle thickness of greater than 10 mm, a sonoelastographic score of 4, and involvement of the entire length of the muscle (group 1) and 30 infants with a sternocleidomastoid muscle thickness of less than 10 mm, a sonoelastographic score of 3, and involvement of only part of the muscle (group 2). A physiatrist performed B-mode sonography and sonoelastography together, measured the thickness of the sternocleidomastoid muscle, and calculated the cross-sectional area of the involved muscle in both groups. On color scale sonoelastography, the sonoelastographic score of the sternocleidomastoid muscle was graded from 1 (purple to green: soft) to 4 (red: stiff), and the color histogram of the muscle was subsequently analyzed.

RESULTS

The thickness and cross-sectional area of the sternocleidomastoid muscles in group 1 were significantly greater than those in group 2 (P = .001). On the color histograms, the median red pixel values in group 1 were significantly greater than those in group 2 (P = .001). In group 1, the mass in the affected muscle completely disappeared in 16 infants (80%), and a residual mass was detected in 4 (20%) on B-mode sonography at the final outcome. However, in group 2, the mass in the affected sternocleidomastoid muscle completely disappeared in all of the infants.

CONCLUSIONS

These findings suggest that real-time sonoelastography, although an ancillary technique to conventional sonography, may predict treatment outcomes of congenital muscular torticollis.

Stretch-induced ERK2 phosphorylation requires PLA2 activity in skeletal myotubes

Mechanical stretch rapidly activates multiple signaling cascades, including phospholipases and kinases, to stimulate protein synthesis and growth. The purpose of this study was to determine whether PLA2 activation contributes to stretch-induced phosphorylation of ERK2 in skeletal muscle myotubes. Myotubes derived from neonatal C57 mice were cultured on silicone membranes and subjected to brief cyclic stretch. Inhibition of PLA2 prevented ERK2 phosphorylation, while inhibition of prostaglandin or leukotriene synthesis did not. ERK2 phosphorylation was also blocked by genistein and PD98059, implicating the canonical raf-MEK-ERK cassette. It appears that PLA2, but not further metabolism of arachidonic acid, is required for stretch-induced activation of ERK2. Exposure to exogenous arachidonic acid had no effect on ERK2 phosphorylation, but exposure to lysophosphatidylcholine, the other metabolite of PLA2, caused a dose-dependent increase in ERK2 phosphorylation. These results suggest that stretch-induced activation of ERK2 may result from an interaction between PLA2 derived lysophosphatidylcholine and membrane receptors.

Effect of indomethacin on force responses and sarcoplasmic reticulum function in skinned skeletal muscle fibers and cytosolic [Ca2+] in myotubes

In this study, the effects of phospholipase A2 (PLA2) inhibitors on excitation-contraction coupling (ECC) and sarcoplasmic reticulum (SR) function were examined in skinned extensor digitorum longus (EDL) muscle fibers of the rat. The nonspecific PLA2 inhibitor indomethacin (200 microM) significantly increased the peak (approximately 2-fold, P = 0.02) and the width (approximately 6-fold, P = 0.008) of depolarization-induced force responses (DIFRs) elicited in the fibers (n = 4). Exposure of the skinned EDL fibers to indomethacin (200 microM) (n = 7) and another PLA2 inhibitor quinacrine (200 microM) (n = 5) resulted in the return of large DIFRs after use-dependent rundown. However, aristolochic acid (100 microM), an inhibitor of secretory PLA2, failed to return DIFRs after rundown. Indomethacin did not protect against the loss of DIFRs induced by exposure to elevated myofibrillar [Ca2+]. Indomethacin (200 microM) produced a small but significant increase in the Ca2+ sensitivity of the contractile apparatus of skinned EDL fibers and the maximum force production. Indomethacin (200 microM) also had significant effects on SR function, increasing SR Ca2+ loading in the skinned fibers (117.2 +/- 3.0% of controls, P = 0.0008, n = 8) and inducing intracellular Ca2+ release in isolated intact flexor digitorum brevis (FDB) fibers (n = 7) and C2C12 myotubes (n = 6). These data suggest that intracellular PLA2 may be an important modulator of ECC in skeletal muscle.

Myopathy in broiler chickens: a role for Ca(2+)-activated phospholipase A2?

The role of Ca(2+)-dependent phospholipase A2 (PLA2) in the mechanism of skeletal muscle damage in broiler chickens was examined in vitro using a novel, synthetic, PLA2-specific inhibitor Ro31-499/001 (Ro31). Muscle damage was assessed by measurement of creatine kinase (CK) efflux from isolated muscles into the incubation medium. Treatment with the specific Ca(2+)-ionophore 4-Br-A23187 (5 microM) caused a 72% elevation (P<0.05) in muscle 45Ca2+ accumulation, which was associated with a marked increase (P<0.001) in muscle CK efflux (7.6-fold). Incubation with Ro31 (50 microM) reduced (P<0.001) CK efflux from muscles treated with ionophore (45%) but was without effect on 45Ca accumulation. Treatment with the Na+ ionophore monensin (100 microM) induced 55% (P< 0.05) elevation in 45Ca2+ accumulation with a concomitant 2.5-fold increase (P<0.001) in CK loss. Muscles incubated with monensin in the presence of Ro31 exhibited a 49% reduction (P<0.001) in CK leakage but showed no change in 45Ca2+ uptake. The results indicate that increasing external Ca2+ entry, directly or indirectly, and elevation of intracellular Ca2+, significantly alters sarcolemmal integrity resulting in increased CK efflux from broiler skeletal muscle. This process is, at least in part, dependent upon activation of PLA2 activity and thus inhibitable by Ro31. It is further proposed that muscle damage in poultry induced by a range of stresses, and insults may also be mediated by a Ro31 sensitive, PLA2-dependent component. The findings have implications for strategies to reduce or prevent myopathies in poultry affecting bird welfare and product quality.

Electro-membrane microcurrent therapy reduces signs and symptoms of muscle damage

PURPOSE

Delayed onset muscle soreness (DOMS) occurs after unaccustomed physical activity or competitive sport, resulting in stiff, painful muscles with impaired function. Acustat electro-membrane microcurrent therapy has been used to treat postoperative pain and soft tissue injury; however, its efficacy in reducing symptoms of muscle damage is not known.

METHODS

Thirty healthy men were recruited for a double-blind, placebo-controlled trial. The muscles of their nondominant arms were damaged using an eccentric-exercise protocol. Subjects were then randomly assigned to treatment with either Acustat or a matching placebo membrane for 96 h and monitored for a total of 168 h.

RESULTS

Subjects in both groups experienced severe pain and swelling of the elbow flexors after the eccentric exercise. After 24 h, the elbow joint angle of the placebo group had increased significantly more than those in the Acustat group (13.7 +/- 8.9 degrees vs 7.5 +/- 5.5 degrees; placebo vs Acustat, P < 0.05), possibly as a consequence of the elbow flexor muscles shortening. For the first 48 h after exercise, maximum voluntary contraction of the elbow flexor muscles was significantly impaired in the placebo group by up to 25% (P < 0.05), whereas muscle function was unchanged in the Acustat group. Peak plasma creatine kinase activity was also lower in the Acustat group (peak = 777 +/- 1438 U.L-1) versus the placebo group (peak = 1918 +/- 2067 U.L-1; (P < 0.05). The membranes were well tolerated by the subjects in both groups without any adverse effects.

CONCLUSION

These data show that treatment of muscle damage with Acustat electro-membrane microcurrent therapy reduces the severity of the symptoms. The mechanisms of action are unknown but are likely related to maintenance of intracellular Ca2+ homeostasis after muscle damaging exercise.

Succinylcholine-associated postoperative myalgia

The subject of postoperative myalgia associated with the use of succinylcholine is reviewed. We discuss the mechanisms of succinylcholine-induced myalgia and the techniques available to prevent and treat the myalgia. In situations where patients are at risk of developing myalgia and succinylcholine is the neuromuscular blocker of choice, the use of a combination of techniques may prove to be a useful strategy.

In vivo microdialysis-A technique for analysis of chemical activators of muscle pain

The accurate measurement of the chemical activators of pain in skeletal muscle has proved to be a major challenge. This study examined the applicability of microdialysis to the measurement of pain-producing substances in skeletal muscle using a defined model of ischemia and reperfusion in the rat. Microdialysis probes were placed into muscle of anesthetized rats. Ischemia was induced for 4 h, followed by reperfusion for 1 h. Perfusates were analyzed for hypoxanthine, potassium, prostaglandin (PG) E(2) and histamine. A 20-fold increase in perfusate hypoxanthine concentration was seen prior to reperfusion (70.1 +/- 27.1 microM for ischemic versus 3.7 +/- 1.9 microM for control; P < 0.05). An initial increase in PGE(2) concentration was seen during ischemia (7.4 +/- 2.0 nM versus 3.4 +/- 1.4 nM; P < 0.05) and immediately post-reperfusion (17.9 +/- 5.2 nM versus 4.0 +/- 1.1 nM; P < 0.05). Potassium concentration was significantly increased following occlusion and reperfusion. This indicates the applicability of microdialysis to the measurement of pain-producing substances in muscle during ischemia and reperfusion. Further use will provide novel information on muscle pain both in defined model systems and in clinical situations in humans.

Evidence of a temperature-sensitive step in the release of prostaglandin E2 in calcium ionophore-stimulated rat muscle

Recent studies have shown that mild hypothermia (32-35 degrees C) confers striking protection against ischemic muscle and neuronal injuries, although the mechanisms are unknown. We previously demonstrated that the release of prostaglandin E2 (PGE2) from metabolically stressed muscles was dependent on calcium and was abolished at or below 35 degrees C. In this study, we examined the temperature response of the release of arachidonic acid (AA) and its cyclooxygenase metabolites, PGE2 and prostaglandin F2 alpha (PGF2 alpha) from rat skeletal muscle in the presence of calcium ionophore A23187, an agent that directly elevates intracellular calcium. Calcium ionophore markedly stimulated the release of AA, PGE2 and PGF2 alpha at 37 degrees C, as expected. Reducing the temperature to 35 degrees C and below sharply decreased PGE2 and PGF2 alpha release but not AA release. The activity of phospholipase A2 stimulated by calcium ionophore was unaffected when temperature of incubation was lowered from 37 to 32 degrees C. The results suggest that reducing temperature from 37 degrees C to 35 degrees C or below inhibits the conversion from free arachidonate to PGs in calcium ionophore-stimulated muscle.

Mechanical stimulation of skeletal muscle increases prostaglandin F2 alpha production, cyclooxygenase activity, and cell growth by a pertussis toxin sensitive mechanism

Repetitive mechanical stimulation of differentiated skeletal muscle in tissue culture increased the long-term production of prostaglandin F2 alpha, an anabolic stimulator of myofiber growth. Within 4 h of initiating mechanical stimulation, the enzymatic activity of cyclooxygenase (prostaglandin GH synthase [PGHS]), a regulatory enzyme in prostaglandin synthesis, was increased 82% (P < .005), and this increase was maintained for at least 24 h. Kinetic analysis of stretch-activated cyclooxygenase activity indicated a two to threefold decrease in the enzyme's Km, with little change in its Vmax. Immunocytochemical analysis of the cell cultures indicated the presence of high levels of the mitogen-inducible isoform of cyclooxygenase (PGHS-2) in the skeletal myofibers compared to the interstitial fibroblasts. While the stretch-induced increase in cyclooxygenase enzymatic activity was not inhibited by tetrodotoxin and therefore was independent of cellular electrical activity, the G protein inhibitor pertussis toxin prevented stretch-induced cyclooxygenase activation. Pertussis toxin also inhibited stretch-induced increases in PGF2 alpha production, phospholipase D activation, and cell growth. It is concluded that stretch of skeletal muscle increases muscle cell growth through a G protein-dependent process involving the activation of cyclooxygenase, an immediate early gene product.

Evidence of two mechanisms of prostaglandin release in an in vitro model of muscle damage. Possible therapeutic implications

In spite of recent progress, treatment of muscle disease based on specific gene therapy is not yet available. An alternative approach is to develop treatment which affords non-specific protection against general factors involved in cell damage. This approach is used effectively to prevent neuronal damage in experimental brain ischemia in animals and has been proposed for human trials. The most effective intervention is the use of mild (35 degrees C) hypothermia. An in vitro model to study muscle cell damage employs the rat epitrochlearis muscle exposed to low concentrations of 2:4-dinitrophenol, an uncoupler of oxidative phosphorylation. The efflux of prostaglandin E2 (PGE2) from the muscle is used as an indicator of muscle damage. We now show that there are two types of PGE2 release. "Basal" efflux gradually declines with decreasing temperatures and is not affected by removal of calcium from the medium. The efflux of PGE2 in response to metabolic stress is dependent on the presence of calcium and is abolished by mild hypothermia of 35 degrees C. The latter effect suggests that cell death is muscle and neurons have features in common and that muscle may be a useful tissue in which to investigate this phenomenon further.

Effects of calcium channel antagonists on the release of prostaglandin E2 from metabolically stressed muscle

Calcium influx plays a critical role in the activation of the arachidonic cascade in muscle damage. We examined the effects of L-type calcium channel antagonists on the release of prostaglandin E2 (PGE2), a bioactive metabolite of arachidonic acid metabolism, from skeletal muscle. The basal release of PGE2 was not affected by calcium channel inhibitors, such as nifedipine and verapamil. The release of PGE2 induced by dinitrophenol, an uncoupler of oxidative phosphorylation, was abolished by nifedipine and verapamil at 50 and 150 microM, respectively. It was not necessary to include the calcium channel blockers in the medium before or at the time of dinitrophenol stimulation to produce the effect on PGE2 release. The release of PGE2 was prevented for as long as calcium channel blockers were present in the medium after the dinitrophenol stress.

Lipase inhibitors abolish contractions and cause depolarization in frog skeletal muscle fibres

Single, intact frog muscle fibers were exposed to bromophenylacylbromide (BPB) or nordihydroguairetic acid (NDGA). Fibres first became unable to respond to electrical stimulation and then depolarized; this process was accelerated by repeated activation. In addition BPB, but not NDGA, eventually induced a contracture in the fibre. The contractile response to direct Ca-release from the sarcoplasmic reticulum by caffeine was unaffected by the drugs.

Mild hypothermia preserves contractile function and inhibits prostaglandin E2 release from metabolically stressed skeletal muscle

An in vitro model of muscle damage was used to investigate the protective effect of mild hypothermia in muscle injury. Rat epitrochlearis muscles were dissected in their entirety and suspended in Krebs-Ringer solution and DNP, a mitochondrial uncoupler, was added. PGE2 and lactate release and the contractile response to stimulation were measured and compared to untreated controls. Experiments were done at 37, 35, 33 and 27 degrees C. At 37 degrees C, DNP stimulated muscle releases large amounts of PGE2 and lactate and is unable to contract. As the temperature is reduced, there is progressive preservation of contractile force, although high lactate levels at the lowest temperatures indicate that the metabolic stress is still present. In contrast, DNP stimulated PGE2 release is completely inhibited at or below 35 degrees C and may be related to a similar protective phenomenon seen in experimental ischemic neuronal death.

Muscle pains and biochemical changes following suxamethonium administration after six pretreatment regimens

The incidence of muscle pains and changes in serum concentrations of potassium, calcium and creatine kinase following suxamethonium were investigated after no pretreatment or pretreatment with intravenous tubocurarine 0.05 mg.kg-1, intravenous chlorpromazine 0.1 mg.kg-1, alphatocopherol (vitamin E) 600 mg in three divided doses orally, aspirin 600 mg orally or intravenous calcium chloride 5 mg.kg-1 in groups of 20 patients each. The incidence of myalgia was reduced significantly by tubocurarine, chlorpromazine and alphatocopherol. However, the increase in creatine kinase was attenuated only in the groups of patients who received tubocurarine and chlorpromazine. The changes in serum potassium and calcium concentrations were within acceptable limits. The intubating conditions were not as good in the patients who received tubocurarine as in the other groups. Effectiveness of chlorpromazine in preventing both the myalgia and the biochemical changes suggests the involvement of phospholipases in the pathogenesis of suxamethonium-induced muscle damage.

Mechanisms of exercise-induced muscle fibre injury

Exercise for which a skeletal muscle is not adequately conditioned results in focal sites of injury distributed within and among the fibres. Exercise with eccentric contractions is particularly damaging. The injury process can be hypothesised to occur in several stages. First, an initial phase serves to inaugurate the sequence. Hypotheses for the initial event can be categorised as either physical or metabolic in nature. We argue that the initial event is physical, that stresses imposed on sarcolemma by sarcomere length inhomogeneities occurring during eccentric contractions cause disruption of the normal permeability barrier provided by the cell membrane and basal lamina. This structural disturbance allows Ca++ to enter the fibre down its electrochemical gradient, precipitating the Ca++ overload phase. If the breaks in the sarcolemma are relatively minor, the entering Ca++ may be adequately handled by ATPase pumps that sequester and extrude Ca++ from the cytoplasm ('reversible' injury). However, if the Ca++ influx overwhelms the Ca++ pumps and free cytosolic Ca++ concentration rises, the injury becomes 'irreversible'. Elevations in intracellular Ca++ levels activate a number of Ca(++)-dependent proteolytic and phospholipolytic pathways that are indigenous to the muscle fibres, which respectively degrade structural and contractile proteins and membrane phospholipids; for instance, it has been demonstrated that elevation of intracellular Ca++ levels with Ca++ ionophores results in loss of creatine kinase activity from the fibres through activation of phospholipase A2 and subsequent production of leukotrienes. This autogenetic phase occurs prior to arrival of phagocytic cells, and continues during the inflammatory period when macrophages and other phagocytic cells are active at the damage site. The phagocytic phase is in evidence by 2 to 6 hours after the injury, and proceeds for several days. The regenerative phase then restores the muscle fibre to its normal condition. Repair of the muscle fibres appears to be complete; the fibres adapt during this process so that future bouts of exercise of similar type, intensity, and duration cause less injury to the muscle.

The nature of the proteins lost from isolated rat skeletal muscle during experimental damage

Sodium dodecyl sulfate-polyacrylamide gel analysis of the incubation media surrounding isolated rat soleus muscles has been used to determine the nature of the proteins lost from skeletal muscle during damage. Following various forms of experimental trauma only selected proteins are lost to the medium when compared to the protein composition of the muscle cytosol. The proteins released do not appear to be released in a size dependent manner and their release is partly inhibited by an absence of calcium in the extracellular medium. alpha-Tocopherol entirely prevents the release of cytosolic enzymes induced by intracellular calcium overload.

Time course of muscle adaptation after high force eccentric exercise

The repeated bout effect on changes in muscle damage indicators was examined in two groups of subjects following two bouts of 70 maximal eccentric actions of the forearm flexors. Fourteen college age female subjects were placed into two groups. The two bouts were separated by 6 weeks (n = 6), and 10 weeks (n = 8). The subjects performed the same amount of work for the bouts. The muscle damage indicators were isometric strength (STR), relaxed elbow joint angle (RANG), flexed elbow joint angle (FANG), perceived muscle soreness ratings (SOR), and plasma creatine kinase activity (CK). These measures were obtained pre-exercise and 5 days following each bout. The first bout showed significant changes in all measures over time for both groups (P less than 0.01). For the 6-week group, significantly smaller changes in RANG (P less than 0.01), SOR (P less than 0.05), and CK (P less than 0.01), as well as significantly faster recoveries (P less than 0.05) for STR and FANG were produced in the second bout. For the 10-week group, significantly smaller changes in RANG (P less than 0.05) and CK (P less than 0.01) were demonstrated by the second bout, but not significant difference was found for STR, FANG, and SOR between bouts 1 and 2. Changes in CK were still significantly smaller than that of the first bout when 6 subjects (3 subjects from each group) performed the same exercise 6 months after the second bout, but no difference in other measures.(ABSTRACT TRUNCATED AT 250 WORDS)

Effects of calcium ionophore on vitamin E-deficient rat muscle

Damage to skeletal muscles may be mediated via free radicals or intracellular calcium overload. To look for inter-relationships between these pathways we have examined the effect of intracellular Ca overload on muscles from rats fed on either a vitamin E-deficient or vitamin E-sufficient diet and assessed the non-enzymic lipid peroxidation in these muscles by examining the production of thiobarbituric acid reactive substances by homogenates. Vitamin E-deficient muscles were more susceptible to Ca-induced intracellular enzyme efflux and this was acutely corrected by supplementation of the external medium with 230 mumol alpha-tocopherol/l. Vitamin E-deficient muscles showed increased levels of basal lipid peroxides and were more susceptible to iron-catalysed lipid peroxidation. Addition of the Ca ionophore A23187 increased lipid peroxidation in vitamin E-deficient muscle homogenates, but had the opposite effect in vitamin E-sufficient muscles. These results demonstrate that vitamin E-deficient muscle has an increased susceptibility to intracellular Ca overload, but that this effect cannot be explained by a direct stimulatory effect of the ionophore on non-enzymic lipid peroxidation.

Protein turnover is elevated in muscle of mdx mice in vivo

mdx mice lack the protein dystrophin, the absence of which causes Duchenne muscular dystrophy in humans. To examine how mdx mice maintain muscle mass despite dystrophin deficiency, we measured protein turnover rates in muscles of mdx and wild-type (C57BL/10) mice in vivo. At all ages studied, rates of muscle protein synthesis and degradation were higher in mdx than in C57BL/10 mice.

Mechanisms of creatine kinase release from isolated rat skeletal muscles damaged by propylene glycol and ethanol

The organic cosolvents propylene glycol and ethanol are found to cause skeletal muscle damage and creatine kinase release following intramuscular injection. The mechanisms of this organic cosolvent-induced enzyme release have not been elucidated. Cosolvent-induced creatine kinase release was enhanced by the addition of calcium to the incubation medium, and inhibited, albeit modestly, by dibucaine, a nonspecific phospholipase A2 inhibitor. The temporal pattern of creatine kinase release further suggested that cosolvent-induced enzyme release from skeletal muscles may be caused by an intracellular mechanism rather than by a direct solubilization of sarcolemma. This intracellular mechanism may involve the mobilization of calcium.

Muscle glutamine concentration and protein turnover in vivo in malnutrition and in endotoxemia

A comparison of the changes in the concentration of glutamine [Gln] in skeletal muscle in a variety of catabolic states with the attendant changes in rates of protein synthesis and degradation indicates a number of substantial correlations which provide insight into both the way in which [Gln] is regulated in muscle and possible regulatory influences of [Gln] on protein balance. There is a striking direct correlation between [Gln] and the rate of protein synthesis in the whole data set. Further examination of this relationship in protein deficiency shows that the changes in [Gln] correlate mainly with the reductions in ribosomal concentration (RNA/protein) and with the decrease in the rate of protein degradation. Because the fall in [Gln] in protein deficiency is also correlated with the decrease in free T3 concentrations, it is suggested that in this case the correlations of [Gln] with rates of protein turnover may be incidental, reflecting thyroidal influences on both protein turnover and glutamine transport. In contrast, in endotoxemia the changes in [Gln] were highly correlated with the ribosomal activity, kRNA, and in this case [Gln] was inversely correlated with the rate of protein degradation. Similar correlated changes occur in starvation and in response to glucocorticoids, and it is suggested that the reductions in [Gln] in endotoxemia could be causally related to the development of insulin resistance and the inhibition of the translational phase of protein synthesis which occurs in these circumstances. The mechanism of the reduction in [Gln] and any linked inhibition of protein synthesis is unknown, but it is shown to be independent of prostaglandin production.(ABSTRACT TRUNCATED AT 250 WORDS)

Oxidative stress and muscular dystrophy

Oxidative stress may be the fundamental basis of many of the structural, functional and biochemical changes characteristic of the inherited muscular dystrophies in animals and humans. The presence of by-products of oxidative damage, and the compensatory increases in cellular antioxidants, both indicate oxidative stress may be occurring in dystrophic muscle. Changes in the proportions and metabolism of cellular lipids, abnormal functions of cellular membranes, altered activity of membrane-bound enzymes such as the SR Ca2+-ATPase, disturbances in cellular protein turnover and energy production and a variety of other changes all indicate that these inherited muscular dystrophies appear more like the results of oxidative stress to muscle than any other type of underlying muscle disturbance. Particular details of these altered characteristics of dystrophic muscle, in combination with current knowledge on the processes of oxidative damage to cells, may provide some insight into the underlying biochemical defect responsible for the disease, as well as direct research towards the ultimate goal of an effective treatment.

Inhibition of Ca2+-induced cytosolic enzyme efflux from skeletal muscle by vitamin E and related compounds

1. Efflux of an intracellular enzyme (creatine kinase) from normal rat skeletal muscles was induced by treatment with the Ca2+ ionophore A23187. Addition of alpha-tocopherol (230 microM) to the incubation medium was found to significantly diminish this efflux, and this effect was mimicked by alpha-tocopherol acetate, phytol and isophytol, but not by Trolox C (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid). 2. Analysis of muscle cation content has shown that these protective effects of alpha-tocopherol etc. are not due to an inhibition of the Ca2+ accumulating effects of the ionophore. 3. Non-enzymic lipid peroxidation of skeletal-muscle homogenates was found to be inhibited by alpha-tocopherol and Trolox C, partially inhibited by phytol and isophytol, but unaffected by alpha-tocopherol acetate. 4. The activity of lipoxygenase enzymes was partially inhibited by alpha-tocopherol, phytol and isophytol, but not by alpha-tocopherol acetate or Trolox C. 5. Prostaglandin E2 efflux from isolated skeletal muscles was stimulated by treatment with the Ca2+ ionophore, but this was unaffected by alpha-tocopherol treatment.

Dystrophin and nebulin in the muscular dystrophies

Skeletal muscle from patients with 5 different forms of muscular dystrophy and from 6 fetuses at high risk (95%) for Duchenne muscular dystrophy (DMD) were probed with specific antibodies for the presence of dystrophin and nebulin. Dystrophin was absent in all 5 patients with DMD and 4 of 6 fetuses at high risk for DMD and present in trace amounts in the remaining two. Dystrophin was also undetectable in one borderline DMD/Becker muscular dystrophy (BMD) case and reduced in 2 of 4 cases of BMD. In contrast, dystrophin was present in all 16 biopsies from 4 other types of muscular dystrophy (congenital, limb girdle, Emery-Dreifuss and facioscapulohumeral). Nebulin profiles varied with the type, severity and duration of the dystrophic process. Nebulin was present in 5 of 6 DMD fetal samples but vastly reduced or absent in all samples of clinically manifest DMD.

Lethal injury by diquat redox cycling in an isolated hepatocyte model

Hepatocyte isolated by collagenase perfusion of livers of male Fischer-344 rats, and treated with 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) (50 microM for 30 min at 37 degrees C) to inhibit glutathione reductase, were significantly more vulnerable to cytotoxicity of the bipyridyl herbicide diquat than similarly treated cells of Sprague-Dawley rats. Without compromise of cell defenses by BCNU, diquat was not cytotoxic to hepatocytes from either strain. Microsomal enzyme induction with phenobarbital (80 mg/kg ip for 3 days before hepatocyte isolation) did not potentiate killing of Fischer hepatocytes by diquat. Specific activities of NADPH-cytochrome P-450 reductase in isolated Fischer and Sprague-Dawley rat liver microsomes utilizing 1 mM diquat as acceptor were 0.085 +/- 0.017 and 0.076 +/- 0.028 mumol/mg.min (mean +/- SEM, N = 5), respectively, indicating the capacity for very active redox cycling of diquat by this route in both strains. The serine protease inhibitor, phenylmethylsulfonyl fluoride (100 microM), had no effect on diquat cytotoxicity, but both leupeptin (100 micrograms/ml) and antipain (50 or 100 microM) were able to delay, through not completely prevent, diquat-induced cell death. The phospholipase inhibitors, chlorpromazine (50 or 100 microM) and dibucaine (50 or 100 microM), similarly delayed but did not prevent cell death. Diquat increased the rate of hepatocyte phospholipid hydrolysis, measured as release into the suspending medium of [14C]arachidonic acid previously incorporated into hepatocyte lipids, but although chlorpromazine decreased phospholipid hydrolysis to the control rate, only partial protection against diquat cytotoxicity was seen. These data suggest that activation of phospholipase A2 and proteases by elevation of cytosolic free Ca2+ cannot account entirely for the loss of cell viability observed in the presence of cytotoxic concentrations of diquat.

Effects of dietary-fish-oil feeding on muscle growth and damage in the rat

1. Giving diets containing 100 g fully-refined, non-hydrogenated fish oil/kg to rats caused substantial modification of skeletal-muscle-membrane fatty acid composition compared with control animals fed on an equivalent diet containing 100 g maize oil/kg. 2. Total muscle arachidonic acid (20:4 omega 6) was reduced from 138 (SD 25) mg/g total fatty acids to 15 (SD 2) mg/g and phospholipid arachidonic acid content showed equivalent changes. 3. Reduction in muscle arachidonic acid content had no influence on the growth of individual muscles. 4. Variation in muscle fatty acid composition exacerbated the response of muscle to calcium-induced damage assessed by efflux of intracellular creatine kinase (EC 2.7.3.2). 5. It is concluded that metabolites of arachidonic acid are unlikely to be primary controlling factors of muscle growth or specific mediators of muscle sarcolemmal damage leading to enzyme efflux.

Calcium ionophore enhances the electron spin resonance signal from isolated skeletal muscle

Electron spin resonance studies of the free radical signal from isolated skeletal muscle during experimental damage have shown that elevation of muscle intracellular calcium with the calcium ionophore A23187 induced an average 61% increase in the amplitude of the signal of g value 2.0047 compared to paired, untreated control muscles, accompanied by a large efflux of intracellular creatine kinase to the external medium. Inhibitors of the calcium-induced loss of cell viability leading to enzyme efflux, i.e., chlorpromazine, phenidone and nordihydroguaiaretic acid had variable effects on the signal, suggesting that the free radical signal obtained from skeletal muscle by electron spin resonance techniques is stimulated by intracellular calcium overload, but is not directly related to the mechanisms by which calcium overload leads to a loss of cell viability leading to intracellular enzyme efflux.

Antibody-induced modulation of the CD3/T cell receptor complex causes T cell refractoriness by inhibiting the early metabolic steps involved in T cell activation

We investigated the mechanism involved in T cell unresponsiveness that follows the monoclonal antibody-induced surface modulation of the CD3-TCR complex. We determined whether modulation of CD3-TCR affected the early metabolic steps such as [Ca2+]i rise and InsP3 formation. A strong inhibition of the increase on [Ca2+]i mediated by either anti-TCR or anti-CD2 mAbs was detected. In contrast, surface modulation of CD2 molecules did not prevent the [Ca2+]i increase induced by anti-TCR mAb. Similarly, InsP3 increase was strongly reduced only after modulation of CD3-TCR complex (but not of CD2 molecules). Therefore, it appears that surface modulation of CD3-TCR complex causes T cell refractoriness by inhibiting the very early metabolic events that follow receptor-ligand interactions.