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PubMed1989

A comparison of muscle precursor replication in crush-injured skeletal muscle of Swiss and BALBc mice.

Muscle precursor replication in Swiss mice, in which muscle regeneration is exceptionally vigorous, was compared with previous data for regeneration in BALBc mice. The tibialis anterior muscles of 23 male and 15 female inbred Swiss SJL/J mice were crush injured, and tritiated thymidine injected into mice at various times after injury to label replicating muscle precursors. Lesion samples were taken 10 days after injury, processed for autoradiography, and grain counts of myotube nuclei analysed. Muscle regeneration was more vigorous in male compared with female Swiss mice, and in both was strikingly greater than that in BALBc mice in which there was extensive fibrous connective tissue throughout the lesions. Autoradiographic analysis showed that muscle precursor replication started at 24 hours in Swiss mice, 6 hours earlier than the onset at 30 hours in BALBc mice. Muscle precursor replication appeared to be more active 96 hours after injury in female Swiss compared with male BALBc and male Swiss mice respectively, although numbers of precursor cells replicating at other times were similar. It is not known whether the slight difference in onset of muscle precursor replication can alone account for the more complete muscle regeneration seen in Swiss mice. Similar studies were carried out in 11 male and 10 female F1 hybrid (SJL/J x BALBc) mice. Analysis of labelled myotube nuclei showed that muscle precursors did not synthesise DNA prior to 30 hours after injury, and regeneration resembled that of the parental BALBc strain.

Animals↗
PubMed1989

Muscle precursor replication after repeated regeneration of skeletal muscle in mice.

We propose that when skeletal muscle regenerates after injury, myogenic precursor cell replication commences earlier if the muscle has undergone a recent previous cycle of regeneration. To test this a series of muscles in mice were crush-injured and allowed to regenerate. Then either 7 or 28 days after the initial injury, the muscles were reinjured. The onset of DNA synthesis in myogenic precursor cells was determined by injecting each mouse once with tritiated thymidine at a specific time after the second injury. All reinjured muscles were left for 10 days to regenerate to the myotube stage. The presence of autoradiographically labelled myotube nuclei indicated that these nuclei were the progeny of myogenic precursors labelled at the time of injection of tritiated thymidine. Thus the onset of muscle precursor cell replication was determined. A similar series of experiments was conducted on muscle autotransplants, injured at 28 days after transplantation and sampled 10 days later. In none of these situations did muscle precursor cell replication occur earlier than in control muscles, which were injured only once, where myogenesis commenced between 24 and 30 h after injury. The autoradiographic data do not support our hypothesis. We conclude that the increased numbers of muscle precursors reported (by various authors) after repeated cycles of regeneration, are not due to the earlier initiation of DNA synthesis in myogenic precursor cells.

Animals↗
PubMed1978

Effect of inhibitors of slow calcium current on rested state contraction of papillary muscles and post rest contractions of atrial muscle of the cat and rabbit hearts.

Effect of Ni, Co and Mn ions and of D-600 on rested state contractions (RSCs) of cat and rabbit papillary muscles and on post rest contractions (PRCs) of cat and rabbit atrial muscle was investigated. Ni and Co in concentration 2 mmol/l reduced the force of RSCs in papillary muscles by 78%, increased the dip between the phase 1 and 2 of respective action potentials (APs), lowered the level of plateau and decreased the total duration of AP. Strong PRCs in atrial muscle were reduced by Ni only by 25%, while the subsequent beats were strongly inhibited. Ni completely inhibited RSCs in papillary muscles increased by caffeine (10 mmol/1) or by reduction in Na concentration by 50%. Mn ions in concentration 1--2 mmol/l inhibited strongly both RSCs in papillary muscles and strong PRCs in atrial muscle, increased the dip between phase 1 and 2 and increased total duration of AP. Mn ions stimulated 45Ca efflux from papillary muscles and atrial strips. D-600 did not affect RSCs nor the shape of respective APs. It is concluded that RSCs in papillary muscles are directly activated by Ca inflow during the respective excitation while strong PRCs in atrial muscle are activated mostly by Ca released from intracellular stores.

Action Potentials↗
PubMed1985

Comparative study of myosins present in the lateral muscle of some fish: species variations in myosin isoforms and their distribution in red, pink and white muscle.

Myosin isoforms and their distribution in the various fibre types of the lateral muscle of eight teleost fish (representing a wide range of taxonomic groups and lifestyles) were investigated electrophoretically, histochemically and immunohistochemically. Polyclonal antisera were raised against slow (red muscle) and fast (white muscle) myosins of the mullet, and used to stain sections of lateral muscle. Antisera specific for fast and slow myosin heavy chains only (anti-FHC and anti-SHC respectively) and for whole fast and slow myosins (anti-F and anti-S respectively) were obtained, and their specificity was confirmed by immunoblotting against electrophoretically separated myofibrillar proteins. The ATPase activity of myosin isoforms was examined histochemically using methods to demonstrate their acid- and alkali-lability and their Ca-Mg dependent actomyosin ATPase. As expected, the predominant myosin (and fibre) type in the red muscle showed an alkali-labile ATPase activity, reacted with the anti-S and anti-SHC sera (but not anti-F or anti-FHC) and contained two 'slow' light chains, whereas the predominant myosin (and fibre) type in the white muscle showed an alkali-stable ATPase activity, reacted with anti-F and anti-FHC sera (but not anti-S or anti-SHC) and contained three 'fast' light chains. However, superimposed upon this basic pattern were a number of variations, many of them species-related. On analysis by two-dimensional gel electrophoresis fish myosin light chains LC1s, LC2s and LC2f migrated like the corresponding light chains of mammalian myosins, but fish LC1f consistently had a more acidic pI value than mammalian LC1f. Fish LC3f varied markedly in Mr in a species-related manner: in some fish (e.g. eel and mullet) the Mr value of LC3f was less than that for the other two light chains (as in mammalian myosin), whereas in others it was similar to that of LC2f (e.g. cat-fish) or even greater (e.g. goldfish). Species differences were also seen in the relative intensity of LC1f and LC3f spots given by the fish fast myosins. In most of the fish examined the red muscle layer showed some micro-heterogeneity, containing (in addition to the typical slow fibres) small numbers of fibres with a histo- and immunohistochemical profile typical of white muscle (fast) fibres. However, other immunohistochemically distinct minority fibres were found in the red muscle of the goldfish. Three types of pink muscle were distinguished: a mosaic of immunohistochemically typical red and white fibres (e.g. grey mullet).(ABSTRACT TRUNCATED AT 400 WORDS)

Anguilla↗
PubMed1994

Muscle phosphoglycerate mutase (PGAM) deficiency in the first Caucasian patient: biochemistry, muscle culture and 31P-MR spectroscopy.

Muscle phosphoglycerate mutase (PGAM) deficiency has been so far identified in only six patients, five of these being African Americans. We report the results of clinical, morphological, biochemical, muscle culture and 31P-MR spectroscopy studies in the first Caucasian patient with muscle PGAM deficiency. A 23-year-old man had a 10-year history of cramps after physical exertion with one episode of pigmenturia. Neurological examination and EMG study were normal. ECG and echocardiography revealed hypertrophy of the interventricular septum and slight dilation of the left chambers of the heart. Muscle biopsy revealed increased glycogen content and some accumulation of mitochondria. Muscle PGAM activity was markedly decreased (6.5% and 9.7% of control value in two different biopsies). Citrate synthase and other mitochondrial respiratory chain enzyme activities were much higher than normal. In contrast to the marked decrease of PGAM activity observed in muscle biopsy, total enzyme activity in the patient's aneural muscle culture was normal, being represented exclusively by BB isoenzyme. The deficiency of PGAM-MM isoenzyme was reproduced in the patient's innervated muscle culture. Muscle 31P-MR spectroscopy showed accumulation of phosphomonoesters only on fast "glycolytic" exercise. On "aerobic" exercise, Vmax, calculated from the work-energy cost transfer function, showed an increase consistent with the morphological and biochemical evidence of mitochondrial proliferation. This might represent a sort of compensatory aerobic effort in an attempt to restore muscle power.

Adult↗
PubMed1994

Low energy charge and high adenosine content in smooth muscle of human bladder in comparison with striated muscle.

This study determined the energy charge, adenosine and inosine content of human bladder smooth muscle in comparison with striated muscle of the same individual. Biopsies were obtained from 21 women who were subjected to urethrocystopexy because of urinary stress incontinence. We found that the ATP content of bladder smooth muscle was only about one-eighth of that of striated muscle. The energy charge of bladder smooth muscle was 0.78 +/- 0.13, which is low compared with striated muscle (0.92 +/- 0.02). The adenosine content of bladder smooth muscle was 6.7 times higher than striated muscle and the adenosine/ATP ratio was 1:9 compared with 1:450 for striated muscle. These findings were in accordance with our previous studies on uterine smooth muscle.

Adenosine↗
PubMed1987

Developmental expression of the muscle-specific isozyme of phosphoglycerate mutase in human muscle cultured in monolayer and innervated by fetal rat spinal cord.

The electrophoretic pattern of phosphoglycerate mutase of adult innervated normal human muscle is composed predominantly of the muscle-specific isozyme, whereas the electrophoretic pattern of aneurally cultured human muscle is composed only of the brain-specific isozyme. We studied the transition of the isozymes (phosphogluterate mutase) in human muscle cultured in monolayer and innervated for 20 to 83 days by rat embryo spinal cord explants. In this culture system, regions of innervated muscle fibers in close proximity to the ventral part of the spinal cord explant continuously contracted and the contractions were reversibly blocked by 1 mM d-tubocurarine. In those innervated cultured human muscle fibers, the total activity of phosphoglycerate mutase was increased and the muscle-specific isozyme was expressed. The amount of muscle-specific isozyme directly correlated with the duration of innervation. This study demonstrated that expression of the gene for the muscle-specific isozyme of phosphoglycerate mutase in human muscle cultured in monolayer is influenced by de novo innervation.

Animals↗
PubMed1982

Incorporation of donor muscle precursor cells into an area of muscle regeneration in the host mouse.

Normal muscle precursor cells, prepared by the enzymatic disaggregation of neonatal mouse muscle, were implanted into an area of regenerating muscle in a genetically different inbred strain. This was done in an attempt to determine, first, whether donor muscle precursor cells prepared in this way would fuse with the developing muscle fibres of the host; and second, whether in the "mosaic" muscle fibres thus formed donor as well as host genes were expressed. As markers of the host and donor genes we used the allelic isoenzyme variants of glucose-6-phosphate isomerase (GPI). In 43 out of 60 grafts we detected the presence of a "hybrid" isoenzyme intermediate between host and donor types. This "hybrid" indicated that donor muscle precursor cells had fused with regenerating host muscle cells, and had expressed their GPI genes within the resulting mosaic muscle fibres. We have developed this technique with a view to inserting normal genes into genetically abnormal myopathic muscle.

Animals↗
PubMed1996

Relation of systemic and local muscle exercise capacity to skeletal muscle characteristics in men with congestive heart failure.

OBJECTIVES: The present study was undertaken to further characterize changes in skeletal muscle morphology and histochemistry in congestive heart failure and to determine the relation of these changes to abnormalities of systemic and local muscle exercise capacity. BACKGROUND: Abnormalities of skeletal muscle appear to play a role in the limitation of exercise capacity in congestive heart failure, but information on the changes in muscle morphology and biochemistry and their relation to alterations in muscle function is limited. METHODS: Eighteen men with predominantly mild to moderate congestive heart failure (mean +/- SEM New York Heart Association functional class 2.6 +/- 0.2, ejection fraction 24 +/- 2%) and eight age- and gender-matched sedentary control subjects underwent measurements of peak systemic oxygen consumption (VO2) during cycle ergometry, resistance to fatigue of the quadriceps femoris muscle group and biopsy of the vastus lateralis muscle. RESULTS: Peak VO2 and resistance to fatigue were lower in the patients with heart failure than in control subjects (15.7 +/- 1.2 vs. 25.1 +/- 1.5 ml/min-kg and 63 +/- 2% vs. 85 +/- 3%, respectively, both p < 0.001). Patients had a lower proportion of slow twitch, type I fibers than did control subjects (36 +/- 3% vs. 46 +/- 5%, p = 0.048) and a higher proportion of fast twitch, type IIab fibers (18 +/- 3% vs. 7 +/- 2%, p = 0.004). Fiber cross-sectional area was smaller, and single-fiber succinate dehydrogenase activity, a mitochondrial oxidative marker, was lower in patients (both p < or = 0.034). Likewise, the ratio of average fast twitch to slow twitch fiber cross-sectional area was lower in patients (0.780 +/- 0.06 vs. 1.05 +/- 0.08, p = 0.019). Peak VO2 was strongly related to integrated succinate dehydrogenase activity in patients (r = 0.896, p = 0.001). Peak VO2, resistance to fatigue and strength also correlated significantly with several measures of fiber size, especially of fast twitch fibers, in patients. None of the skeletal muscle characteristics examined correlated with exercise capacity in control subjects. CONCLUSIONS: These results indicate that congestive heart failure is associated with changes in the characteristics of skeletal muscle and local as well as systemic exercise performance. There are fewer slow twitch fibers, smaller fast twitch fibers and lower succinate dehydrogenase activity. The latter finding suggests that mitochondrial content of muscle is reduced in heart failure and that impaired aerobic-oxidative capacity may play a role in the limitation of systemic exercise capacity.

Aged↗
PubMed2006

The effects of botulinum neurotoxin A induced muscle paresis during a critical period upon muscle and spinal cord development in the rat.

The second postnatal week is a critical period in rat motor development. The expansion of corticospinal innervation coincides with elimination of polyneuronal innervation of muscles, onset of quadrupedal locomotion and refinement of muscle afferent input to the ventral horn. Such developmental events are believed to be activity-dependent. In the present study, muscle afferent activity was temporarily reduced by injecting distal forelimb muscles with botulinum toxin A (BTX). Injections of toxin or saline were made unilaterally on postnatal day (P) 7 which in BTX-treated animals lead to a profound loss of movement in the affected limb over the next week before function returned. The neural tracer cholera toxin B (CTB) was injected into the extensor digitorum communis (EDC) at either P14 or P28. Allowing 3 days for tracer transport, the spinal cords were sectioned and immunostained for CTB and cJun. In separate experiments, behavioural testing of the forelimb was carried out between P35 and P49. Then, sections of EDC muscle were immunostained for slow myosin. An increased density of ventral horn muscle afferent boutons was observed at P17 in BTX-treated animals compared to controls, however, by P31, this difference was not significant. However, CTB labelling also revealed significantly increased motor axon terminals in the ventral Renshaw cell region in BTX-treated animals at P31, accompanied by raised expression of cJun in ipsilateral motoneurones. BTX-treated animals showed deficits in ladder walking, and their muscles contained a higher density and significantly more clustering of slow myosin expressing muscle fibres than controls. Temporary reduction in activity did not significantly alter muscle afferent development, but temporary blockade of neuromuscular junctions did affect both muscle and motor axon, in the longer term.

Age Factors↗
PubMed2006

Unilateral lateral rectus muscle recession and medial rectus muscle resection with or without advancement for postoperative consecutive exotropia.

PURPOSE: To evaluate the effectiveness of unilateral lateral rectus muscle recession and medial rectus muscle resection with or without advancement in treating postoperative consecutive exotropia. METHODS: We performed a retrospective review on 31 patients with consecutive exotropia who were treated with unilateral lateral rectus muscle recession and medial rectus muscle resection (17 patients) or unilateral lateral rectus muscle recession and medial rectus muscle partial resection combined with advancement (14 patients). All patients had exotropia with a less than 10 prism diopters (PD) distance near-disparity. The characteristics studied before surgery included type of esotropia surgery, detection of amblyopia, presence of an "A" or "V" pattern, dissociated vertical deviation, limitation of adduction, deviation angle measurement, and forced duction testing. Ocular alignment and status of adduction postoperatively at the last follow-up were recorded. RESULTS: Nineteen patients (61.3%) had amblyopia, 17 patients (54.8%) had limitation of adduction, 8 patients (25.8%) had dissociated vertical deviation, and 5 patients (16.1%) had an "A" or "V" pattern. The mean preoperative exodeviation was 47.3 PD. Overall 21 (67.7%) of 31 patients achieved a successful postoperative result (alignment within 10 PD of orthophoria). There was no significant difference in successful alignment in patients treated with unilateral medial rectus muscle resection compared with those treated with unilateral medial rectus muscle partial resection combined with advancement. There was no influence of amblyopia on the result. Twelve (70.6%) of the 17 patients with limited adduction preoperatively showed normalization of adduction postoperatively. CONCLUSIONS: Unilateral lateral rectus muscle recession and medial rectus muscle resection with or without advancement is an effective alternative for treating postoperative consecutive exotropia.

Adolescent↗
PubMed1998

Skeletal muscle myosin heavy chain expression in rats with monocrotaline-induced cardiac hypertrophy and failure. Relation to blood flow and degree of muscle atrophy.

BACKGROUND: In congestive heart failure (CHF) the skeletal muscle of the lower limbs develops a myopathy characterised by atrophy and shift from the slow to the fast type fibres. The mechanisms responsible for these changes are not clear yet. OBJECTIVES: We investigated the influence of blood flow and degree of muscle atrophy on the myosin heavy chains (MHC) composition of the soleus and extensor digitorum longus (EDL) of rats with right ventricle hypertrophy and failure. METHODS: CHF was induced in 16 rats by injecting 30 mg/kg monocrotaline. Eight animals had the same dose of monocrotaline but resulting in compensated right ventricle hypertrophy. Two age- and diet-matched groups of control animals (nine and five respectively) were also studied. The relative percentage of MHC1 (slow isoform), MHC2a (fast oxidative) and MHC2b (fast glycolytic) was determined by densitometric scan after electrophoretic separation. The relative weights of soleus and EDL (muscle weight/body weight) were taken as an index of muscle atrophy. Skeletal muscle blood flow was measured by injecting fluorescent micropheres. RESULTS: CHF and Control (Con) rats showed similar degree of atrophy both in soleus (0.40 +/- 0.06 vs. 0.44 +/- 0.06 p = NS), and EDL (0.47 +/- 0.04 vs. 0.45 +/- 0.02, p = 0.09). In CHF rats these two muscles showed a statistically significant MHCs redistribution toward the fast type isozymes. In fact in EDL of CHF rats MHC2a was 30.5 +/- 6.1% vs. 35.8 +/- 8.6% of the Con (p < 0.05). MHC2b was however higher (68.5 +/- 6.6% vs. 61.0 +/- 9.6%, p = 0.017). In the soleus of CHF rats MHC1 was decreased (87.6 +/- 3.4% vs. 91.9 +/- 5.2%, p = 0.02), while MHC2a was increased (12.04 +/- 3.5% vs. 7.9 +/- 5.2%; p = 0.028). Similar changes were not found in the muscles of the compensated hypertrophy animals. No correlation was found between MHC pattern and the relative muscle weight in the CHF animals. Soleus blood flow in CHF rats was significantly lower than that of Con (0.11 +/- 0.03 ml/min/g vs. 0.22 +/- 0.03 p < 0.05), while no differences were found in EDL (0.06 +/- 0.02 ml/min/g vs. 0.08 +/- 0.02, p = NS). CONCLUSIONS: In rats with CHF a skeletal muscle myopathy characterised by a shift of the MHCs toward the fast type isoforms occurs. The magnitude of the shift correlates neither with the degree of atrophy, nor with the skeletal muscle blood flow, suggesting that these two factors do not play a pivotal role in the pathogenesis of the myopathy.

Animals↗
PubMed2000

Muscle sparing thoracotomy: a biomechanical analysis confirms preservation of muscle strength but no improvement in wound discomfort.

OBJECTIVES: This study compares the posterior auscultatory triangle thoracotomy incision (muscle sparing) with full posterolateral thoracotomy (where latissimus dorsi muscle is always cut across its full width), with particular attention to the difference between latissimus dorsi muscle strength, post operative pain and chronic wound related symptoms. METHODS: Ten patients who had undergone auscultatory triangle thoracotomy (ATT) at least 1 year previously were matched with ten patients who had undergone posterolateral thoracotomy (PLT). Each pair was matched for age, sex, dominant hand, side of the operation, time since operation and presence or absence of history of previous muscle training. Latissimus dorsi muscle strength was assessed by testing the shoulder adduction strength through an arc of 90-0 degrees using isokinetic technique. Early post-operative pain was assessed indirectly by calculating the analgesic requirement in the first 5 post-operative days. A subjective assessment of chronic post-thoracotomy pain was made using a questionnaire presented to the patients at the time of muscle testing. Variability of the torque curves, recorded as coefficient of variance at the time of muscle strength testing, provided objective measurements of chronic pain. Data were analysed using two sample t-tests. RESULTS: All patients reported at least one chronic post-thoracotomy symptom. There was no significant difference between the two groups in terms of acute or chronic wound pain and other long term wound related symptoms. Shoulder adduction strength was 24% greater in ATT than PLT (95% confidence limits=1-43%, P=0.04). CONCLUSIONS: All thoracotomy patients have long term wound related symptoms. This situation is not improved by performing a muscle sparing incision. However thoracotomy through the triangle of auscultation can preserve latissimus dorsi strength which is compromised in a posterolateral thoracotomy incision. We therefore recommend that a muscle sparing thoracotomy be considered for patients where preservation of muscle strength is deemed important, providing the operation is not compromised due to inadequate access.

Adolescent↗
PubMed1983

Muscle pioneers: large mesodermal cells that erect a scaffold for developing muscles and motoneurones in grasshopper embryos.

During embryonic development, muscles differentiate in the appropriate places and motoneurone growth cones find the appropriate muscles; both events occur concurrently and with remarkable specificity. What are the cellular interactions that orchestrate this coordinated development of nerve and muscle? In the development of vertebrate skeletal muscles, motoneurone growth cones arrive in the periphery along stereotyped routes and enter the appropriately located masses of mesodermal cells usually before differentiated muscle fibres appear and before the masses cleave into separate muscles. We find that a similar sequence of events occurs in the grasshopper embryo. We are interested in how mesodermal cells become organized into the appropriate muscles and what guides motoneurone growth cones to their appropriate targets. Fortunately, in the grasshopper embryo the mesodermal cells in the periphery and motoneurones in the central nervous system (CNS) are large, accessible and in many cases individually identifiable from early in their development. We report here the discovery of a class of large mesodermal cells, which we call muscle pioneers, that arise early in development when the embryonic environment is relatively simple and distances short. By their growth and association with particular sites along the ectoderm, the muscle pioneers appear to erect a scaffold for later developing muscles and motoneurone growth cones.

Animals↗
PubMedDate not supplied

Light-chain phosphorylation controls the conformation of vertebrate non-muscle and smooth muscle myosin molecules.

Phosphorylation of the 20,000-molecular weight (Mr) light chains of vertebrate non-muscle (thymus) and smooth muscle (gizzard) myosins regulates the assembly of these myosins into filaments in vitro. At physiological ionic strength and pH, nonphosphorylated smooth muscle and non-muscle myosin filaments are disassembled by stoichiometric levels of MgATP, forming species having sedimentation coefficients of approximately 11S (range 10-12S; myosin monomers in high salt sediment at 6S). When the 20,000 (20K)-Mr light chains on these 11S myosin species are phosphorylated by the light-chain kinase/calmodulin-Ca2+ complex, the inhibitory effect of the light chains on filament formation is removed and the myosins reassemble into filaments which are stable in MgATP. It was originally suggested that the 11S myosin species was a dimer, previously suggested as a building block for smooth muscle and non-muscle myosin filaments. It has since been shown, however, that 11S smooth muscle myosin is monomeric and has a folded conformation rather than the extended shape characteristic of monomeric myosin in high salt. Here we show that 11S non-muscle myosin is also folded and that phosphorylation of the 20K-Mr light chains of both vertebrate non-muscle (thymus) and vertebrate smooth muscle (gizzard) myosins causes these folded 11S molecules to unfold into the conventional extended monomeric form, which is able to assemble into filaments.

Animals↗
PubMed1995

Ischaemia-induced expression of bFGF in normal skeletal muscle: a potential paracrine mechanism for mediating angiogenesis in ischaemic skeletal muscle.

To test the hypothesis that induction of endogenous bFGF can lead to angiogenesis in ischaemic skeletal muscle, we studied the expression of bFGF after transposition of a well-vascularized muscle flap onto an ischaemic hindlimb in the rabbit. The results indicated a marked induction of bFGF mRNA throughout the myoblasts of the well-perfused muscle flap but not the myoblasts of the ischaemic muscle. bFGF protein was detected in the muscle flap, particularly in the myoblasts located closest to a newly formed, adjacent interface, and in the interface itself. In contrast, bFGF expression was not induced after transposition of a well-perfused muscle flap onto healthy muscle tissue. These data provide evidence that the juxtaposition of ischaemic skeletal muscle with healthy mesenchymal tissue triggers an increased expression of bFGF in the myoblasts of the well-perfused muscle. This paracrine induction of bFGF, in turn, leads to increased angiogenesis and regeneration of the ischaemic skeletal muscle.

Animals↗
PubMed1994

Expression of vesicle-associated membrane protein 2 (VAMP-2)/synaptobrevin II and cellubrevin in rat skeletal muscle and in a muscle cell line.

Molecular studies have identified a family of synaptic vesicle-associated membrane proteins (VAMPs, also known as synaptobrevins) which have been implicated in synaptic vesicle docking and/or fusion with plasma membrane proteins. Here we demonstrate the expression of two members of this family, VAMP-2/synaptobrevin II and cellubrevin, in skeletal muscle, a tissue with both constitutive and regulated membrane traffic. The 18 kDa VAMP-2 polypeptide was detected in purified membrane fractions from adult skeletal muscle and from L6 myotubes in culture, demonstrating that the presence of this protein in the isolated muscle membrane fractions is not the result of contamination by ancillary tissues such as peripheral nerve. Furthermore, skeletal muscle and the muscle cell line also expressed cellubrevin, a VAMP-2 homologue of 17 kDa; which is much less abundant in brain cells. Both VAMP-2 and cellubrevin were preferentially isolated in membrane fractions rich in plasma membranes, and were less concentrated in light microsomes and other internal membrane fractions of mature muscle or muscle cells in culture. Interestingly, both VAMP-2 and cellubrevin were much more abundant in the differentiated L6 myotubes than in their precursor myoblasts, suggesting that they are required for functions of differentiated muscle cells. The identity of both polypeptides was further confirmed by their susceptibility to proteolysis by Clostridium tetanus toxin. Expression of these products was further established by the presence of mRNA transcripts of VAMP-2 and cellubrevin, but not of VAMP-1, in both skeletal muscle and L6 myotubes. In contrast, other synaptic vesicle and docking/fusion components were undetectable, such as VAMP-1, SNAP25 and syntaxin 1A/1B, as were synaptophysin and synapsin Ia/Ib, proteins which are believed to be involved in sensing the signal for neuronal exocytosis. It is concluded that VAMP-2 and cellubrevin are expressed in skeletal muscle cells and may each participate in specific processes of intracellular membrane traffic.

Amino Acid Sequence↗
PubMed1999

Ex vivo evaluation of a roller screw linear muscle actuator for an implantable ventricular assist device using trained and untrained latissimus dorsi muscles.

In this study, the power output and contraction length of trained and untrained canine latissimus dorsi (LD) muscles were measured using a roller screw linear muscle actuator (RSLMA). The RSLMA consisted of a roller screw-nut assembly and translation unit to convert the linear pull force of the muscle into an axial displacement of the roller screw. When a cable wound around a spool attached at each end of the roller screw nut was pulled in either direction, the nut was rotated which in turn advanced the roller screw in the axial direction. Under anesthesia, a Telectronics myostimulator (Model 7220) was implanted in the subcutaneous area of the canine left thoracic region with its bipolar intramuscular leads implanted around the thoracodorsal nerve and the distal muscle. A total of 6 dogs went through the myostimulator implantation, followed with 8 weeks of continuous stimulation. After completion of the training, the contraction lengths of the trained and untrained LD muscles were measured, and they were 4.25 and 5.5 cm, respectively, while the instantaneous power outputs were 4.24 and 8 W, respectively. Although untrained muscles could provide much higher instantaneous power immediately following the start of the stimulation, it diminished rapidly. On the other hand, the trained muscle showed prolonged fatigue resistance. The thoracolumbar and humeral approaches in attaching the actuator cable did not show a difference with respect to muscle power output. The trained LD muscle can provide sufficient power in the range of 3-4 W to drive a left heart assist device, but its long-term evaluation awaits development of an appropriate muscle-device interface for chronic in vivo application.

Animals↗