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PubMed1954

Electron microscope studies on ultrathin sections of muscle.

Thin sections of striated muscle from frog (sartorius), rabbit (psoas), rat (heart), and fly (flight muscle), and of smooth muscle from clam (adductor) have been obtained using a new microtome. Electron micrographs of them are presented. The sections are sufficiently thin to achieve a resolution of 30 to 40 A. In fly flight muscle, the myofibrils are distinct and well separated morphological units. In frog and rabbit muscle the myofibrils appear to be so closely packed under normal conditions that their identity as separate units is almost lost. In all types of striated muscle examined, it was found that the filaments are arranged within the myofibrils in a continuous and highly regular hexagonal array. The diameter of the filaments in embedded, sectioned muscle appears to be significantly less than that observed in dried shadowed material. The 400 A axial period, observed in frog and rabbit muscle, and in rat heart muscle, was found to extend across the interstitial material between the filaments. The significance of these findings is discussed.

Animals↗
PubMed1971

Does curare affect transmitter release?

1. The effect of curare on the amount of transmitter released by a nerve stimulus was studied in frog and rat nerve-muscle preparations using electrophysiological techniques.2. When the frog sartorius nerve-muscle preparation was exposed to low doses of curare, the amplitudes of spontaneous miniature end-plate potentials and end-plate currents (e.p.c.s, measured under ;voltage clamp' conditions) were reduced to the same extent, suggesting that the drug did not alter the number of transmitter quanta released by nerve stimulation.3. With higher doses of curare in frog muscle treated with glycerol to abolish twitching, quantum content was estimated from the coefficient of variation (CV) of e.p.c.s. The measured CV increased slightly in curare; this increase probably resulted from a relatively greater contribution of random noise to the observed fluctuations when the e.p.c. was reduced by curare.4. In the rat diaphragm, muscle fibres were cut to block twitching. This procedure produced, among other changes, a reduction in the muscle fibre space constant, so that junctional signals were distorted by the cable properties of the muscle fibre when, as often occurred, micro-electrodes were more than 100-200 mu from the end-plate focus. This produced errors in estimates of quantum content; when these errors were accounted for, it appeared that curare did not significantly alter quantum content.5. It is concluded that if curare affects transmitter release at all, its effect must be much smaller than its well known post-synaptic blocking action.

Animals↗
PubMed1989

The contracting muscle: a challenge for freeze-substitution and low temperature embedding.

Frog sartorius and semitendinosus muscles are quick-frozen either in the resting state or during contraction by means of a LN2 cooled falling copper block. The frozen specimens are freeze-substituted (acetone + OsO4 + uranyl acetate) in a REICHERT JUNG CS auto and either embedded in Spurr's resin and polymerised at a high temperature (60 degrees C) or embedded and polymerised in the Lowicryls K4M, K11M or HM23 at low temperatures (below -30 degrees C). Excellent morphological results are obtained when freeze-substitution, embedding and polymerisation are all carried out below -50 degrees C. Muscles in which a major portion of cellular K+ ions has been replaced by electron dense Cs+ or Tl+ ions are also cryofixed at rest or during contraction, freeze-substituted in pure acetone for 1 week at -80 degrees C and polymerised in K11M at -60 degrees C. A characteristic uneven distribution of the electron dense ions--known from earlier published control experiments--can be observed in sections of resting muscles. Electrically stimulated muscles show ion redistribution. It is concluded that freeze-substitution and low temperature embedding of quick-frozen contracting muscle may be used to investigate changes of ultrastructure, redistribution of cellular water and intracellular movements of mobile ions during muscle contraction.

Animals↗
PubMed1983

Lateral forces in the filament lattice of vertebrate striated muscle in the rigor state.

The repulsive pressure between filaments in the lattice of skinned rabbit and frog striated muscle in rigor has been measured as a function of interfilament spacing, using the osmotic pressure generated by solutions of large, uncharged polymeric molecules (dextran and polyvinylpyrrolidone). The pressure/spacing measurements have been compared with theoretically derived curves for electrostatic pressure. In both muscles, the major part of the experimental curves (100-2,000 torr) lies in the same region as the electrostatic pressure curves, providing that a thick filament charge diameter of approximately 30 nm in rabbit and approximately 26 nm in frog is assumed. In chemically skinned or glycerol-extracted rabbit muscle the fit is good; in chemically skinned frog sartorius and semitendinosus muscle the fit is poor, particularly at lower pressures where a greater spacing is observed than expected on theoretical grounds. The charge diameter is much larger than the generally accepted value for thick filament backbone diameter. This may be because electron microscope results have underestimated the amount of filament shrinkage during sample preparation, or because most of the filament charge is located at some distance from the backbone surface, e.g., on HMM-S2. Decreasing the ionic strength of the external solution, changing the pH, and varying the sarcomere length all give pressure/spacing changes similar to those expected from electrostatic pressure calculations. We conclude that over most of the external pressure range studied, repulsive pressure in the lattice is predominantly electrostatic.

Animals↗
PubMed1983

Myosin light chain and membrane protein phosphorylation in various muscles.

Phosphorylation of myosin light chain was compared in various muscles. In 32P-labeled chicken anterior latissimus dorsi and posterior latissimus dorsi the [32P]phosphate content of the 19,000-dalton and 18,000-dalton light chains, respectively, was 1.8-fold higher in muscles tetanized for 5 or 15 s than in the contralateral resting muscles. Similar results had been previously obtained with frog sartorius and semitendinosus muscles. In addition to the radioactive technique, the extent of light chain phosphorylation was also measured by densitometry after separating the phospho and dephospho forms of the light chain with two-dimensional gel electrophoresis. The extent of light chain phosphorylation in tetanized chicken muscles and caffeine-treated frog muscles was not greater than 50%. The extent of phosphorylation of the 19,000-dalton light chain in hearts from several animals (turtle, rat, frog, chicken, dog, and cat) showed major differences. At the extremes it was 76% in turtle and 10% in chicken. the polymorphism of heart light chain was also demonstrated. Not only myosin light chains but also membrane proteins were detected to be phosphorylated. Some of the membrane proteins exhibited increases in phosphorylation during muscle contraction.

Animals↗
PubMed2001

Proprioceptive modulation of hip flexor activity during the swing phase of locomotion in decerebrate cats.

This study examined the influence of proprioceptive input from hip flexor muscles on the activity in hip flexors during the swing phase of walking in the decerebrate cat. One hindlimb was partially denervated to remove cutaneous input and afferent input from most other hindlimb muscles. Perturbations to hip movement were applied either by 1) manual resistance or assistance to swing or by 2) resistance to hip flexion using a device that blocked hip flexion but allowed leg extension. Electromyographic recordings were made from the iliopsoas (IP), sartorius, and medial gastrocnemius muscles. When the hip was manually assisted into flexion, there was a reduction in hip flexor burst activity. Conversely, when hip flexion was manually resisted or mechanically blocked during swing, the duration and amplitude of hip flexor activity was increased. We also found some specificity in the role of afferents from individual hip flexor muscles in the modulation of flexor burst activity. If the IP muscle was detached from its insertion, little change in the response to blocking flexion was observed. Specific activation of IP afferent fibers by stretching the muscle also did not greatly affect flexor activity. On the other hand, if conduction in the sartorius nerves was blocked, there was a diminished response to blocking hip flexion. The increase in duration of the flexor bursts still occurred, but this increase was consistently lower than that observed when the sartorius nerves were intact. From these results we propose that during swing, feedback from hip flexor muscle afferents, particularly those from the sartorius muscles, enhances flexor activity. In addition, if we delayed the onset of flexor activity in the contralateral hindlimb, blocking hip flexion often resulted in the prolongation of ipsilateral flexor activity for long periods of time, further revealing the reinforcing effects of flexor afferent feedback on flexor activity. This effect was not seen if conduction in the sartorius nerves was blocked. In conclusion, we have found that hip flexor activity during locomotion can be strongly modulated by modifying proprioceptive feedback from the hip flexor muscles.

Animals↗
PubMed1980

Myosin light chain phosphorylation during the contraction cycle of frog muscle.

Changes in the [32P]phosphate content of proteins during contraction were investigated with sartorius and semitendinosus muscles dissected from live frogs injected with [32P]orthophosphate. During a single tetanus, the only significant change was the increase in the [32P]phosphate content of the 18,000-dalton light chain of myosin. The extent of light chain phosphorylation was a function of stimulus duration and it amounted maximally to 0.35 mol of [32P]phosphate transferred per mol of light chain. The extent of phosphorylation in stimulated and stretched semitendinosus muscles, which were unable to produce active tension, was nearly identical to that in muscles stimulated at standard rest length, when the time of stimulation was over a half-second. Maximal light chain phosphorylation was also observed in muscles treated with caffein. These results provide evidence for the activation of the light chain kinase in the intact muscle through a process involving Ca2+. The phosphorylation of the light chain associated with tetanic stimulation was reversible. After short tetanuses, dephosphorylation of light chain approximately followed relaxation and after longer tetanuses, dephosphorylation lagged behind relaxation. The role of light chain phosphorylation was investigated in caffeine-treated and untreated muscles by measuring the Ca content of actin and the [32P]phosphate content of light chain. Phosphorylation of light chain protected the actin-bound Ca against removal by EDTA stoichiometrically. It is postulated that the physiological role of light chain phosphorylation is to increase the rate of combination of the cross-bridges with the actin filaments in the contracting phase of the mechanical activity.

Animals↗
PubMed1982

Release of creatine kinase and lactate dehydrogenase from frog skeletal muscles treated with imipramine.

Frog sartorius and extensor longus digiti IV ("toe") muscles were mounted in sample collecting units, isometric tension was recorded and the activities of creatine kinase and lactate dehydrogenase released into the bathing medium were measured. Addition of imipramine (greater than 0.2 mM) to the control medium induced muscle contractures and increased the rates of enzyme release. Electronmicrographs of muscles exposed to imipramine (0.5--1.0 mM) showed fibers in which the extracellular marked horseradish peroxidase was detected in the sarcoplasm. Both the enzyme-releasing and the contractile effects of imipramine were inhibited by procaine (but not by lidocaine) and were enhanced by replacement of external chloride ions with propionate. The data are consistent with the suggestion that events associated with tension development contribute greatly to the imipramine-induced loss of sarcoplasmic enzymes from frog skeletal muscles. The elevated Ca++ concentration in the sarcoplasm during the imipramine-induced contracture is thought to lead to changes in the plasma membrane that account for the increased enzyme loss and for the penetration of horseradish peroxidase into the sarcoplasm.

Animals↗
PubMed1989

Histochemical fiber types in the thigh muscles of 4 chicken inbred lines.

Distribution, frequency and diameter of fiber types were ascertained in the thigh muscles of I, C, W and M chicken inbred lines. The iliotibialis posterior muscle is composed of FOG and FG types uniformly distributed over the whole muscle cross-section. Three fiber types are demonstrated in the sartorius and semimembranosus muscles. In the superficial regions, the FOG and FG types are present only. Avian SO type appears down into the depth of the muscles. The frequency of this type and FOG type gradually increases in this direction whereas the proportion of FG type decreases. Semimembranosus muscle shows generally higher percentage of FOG fibers and lower frequency of remaining two types. Differences between inbred lines in fiber type frequencies are mostly insignificant. However, the M line with the highest live and muscle weights shows larger fiber diameter of FG and FOG types than I, C and W lines.

Animals↗
PubMed1987

Cat hindlimb motoneurons during locomotion. II. Normal activity patterns.

Activity patterns were recorded from 51 motoneurons in the fifth lumbar ventral root of cats walking on a motorized treadmill at a range of speeds between 0.1 and 1.3 m/s. The muscle of destination of recorded motoneurons was identified by spike-triggered averaging of EMG recordings from each of the anterior thigh muscles. Forty-three motoneurons projected to one of the quadriceps (vastus medialis, vastus lateralis, vastus intermedius, or rectus femoris) or sartorius (anterior or medial) muscles of the anterior thigh. Anterior thigh motoneurons always discharged a single burst of action potentials per step cycle, even in multifunctional muscles (e.g., sartorius anterior) that exhibited more than one burst of EMG activity per step cycle. The instantaneous firing rates of most motoneurons were lowest upon recruitment and increased progressively during a burst, as long as the EMG was still increasing. Firing rates peaked midway through each burst and tended to decline toward the end of the burst. The initial, mean, and peak firing rates of single motoneurons typically increased for faster walking speeds. At any given walking speed, early recruited motoneurons typically reached higher firing rates than late recruited motoneurons. In contrast to decerebrated cats, initial doublets at the beginning of bursts were seen only rarely. In the 4/51 motoneurons that showed initial doublets, both the instantaneous frequency of the doublet and the probability of starting a burst with a doublet decreased for faster walking speeds. The modulations in firing rate of every motoneuron were found to be closely correlated to the smoothed electromyogram of its target muscle. For 32 identified motoneurons, the unit's instantaneous frequencygram was scaled linearly by computer to the rectified smoothed EMG recorded from each of the anterior thigh muscles. The covariance between unitary frequencygram and muscle EMG was computed for each muscle. Typically, the EMG profile of the target muscle accounted for 0.88-0.96 of the variance in unitary firing rate. The EMG profiles of the other anterior thigh muscles, when tested in the same way, usually accounted only for a significantly smaller fraction of the variance. Brief amplitude fluctuations observed in the EMG envelopes were usually also reflected in the individual motoneuron frequencygrams. To further demonstrate the relationship between unitary frequencygrams and EMG, EMG envelopes recorded during walking were used as templates to generate depolarizing currents that were applied intracellularly to lumbar motoneurons in an acute spinal preparation.(ABSTRACT TRUNCATED AT 400 WORDS)

Action Potentials↗
PubMedDate not supplied

[Effect of verapamil and anesthetics on the level of sodium and potassium ions in frog muscles. Role of hydrophobic interactions].

Verapamil, general and local anesthetics influences on ionic contents of frog sartorius and cardiac muscles in respect with these drugs hydrophobicity were studied to clarify the role of verapamil hydrophobic interactions in its physiological activity. It was found that concentration thresholds of the agents toxicities were linearly linked with their hydrophobicity (in logarithmic scale). This relationship provides support for our conclusion that verapamil, general and some local anesthetics are the members of a single drug family. It is a reason to believe that a hydrophobic mechanism of general anesthetic action on cellular structure is the same as a mechanism of verapamil activity in muscles. It is possible that verapamil is accepted as medical drug exactly due to optimum combination of high verapamil hydrophobicity with its structural complementarity to receptor site responsible for use-dependent channel blocking.

Anesthetics↗
PubMed2004

Ectopic expression of Hoxd10 in thoracic spinal segments induces motoneurons with a lumbosacral molecular profile and axon projections to the limb.

Hox genes encode anterior-posterior identity during central nervous system development. Few studies have examined Hox gene function at lumbosacral (LS) levels of the spinal cord, where there is extensive information on normal development. Hoxd10 is expressed at high levels in the embryonic LS cord but not the thoracic cord. To test the hypothesis that restricted expression of Hoxd10 contributes to the attainment of an LS identity, and specifically an LS motoneuron identity, Hoxd10 was ectopically expressed in thoracic segments in chick embryos by means of in ovo electroporation. Regional motoneuron identity was assessed after the normal period of motoneuron differentiation. Subsets of motoneurons in transfected thoracic segments developed a molecular profile normally shown by LS motoneurons, including Lim 1 and RALDH2 expression. In addition, motoneurons in posterior thoracic segments showed novel axon projections to two muscles in the anterodorsal limb, the sartorius and anterior iliotibialis muscles. At thoracic levels, we also found a decrease in motoneuron numbers and a reduction in gonad size. These last findings suggest that early and high levels of Hox expression impeded motoneuron development and neural-mesodermal interactions. Despite these adverse effects, our data indicate that Hoxd10 expression is sufficient to induce LS motoneuron identity and axon trajectories characteristic of motoneurons in the LS region.

Aldehyde Oxidoreductases↗
PubMed1993

Use of mu-conotoxin GIIIA for the study of synaptic transmission at the frog neuromuscular junction.

We have looked at the effect of synthetic mu-conotoxin GIIIA, a selective blocker of muscle Na channels, on various parameters of synaptic transmission at the frog sartorius nerve-muscle preparation. We found that 5 microM mu-conotoxin consistently blocked muscle action potentials, but had no effect on nerve action potentials. The toxin also had no effect on the amplitude or frequency of miniature endplate potentials (MEPPs), on the amplitude or time course of endplate potentials (EPPs), or on stimulation-induced changes in EPP amplitude. The lack of an effect of synthetic mu-conotoxin GIIIA on transmitter release makes this toxin an invaluable tool in the study of neuromuscular transmission under conditions of normal levels of release.

Action Potentials↗
PubMed1975

Enzyme activities in red and white muscles of guinea-pigs and rabbits indigenous to high altitude.

The activities of several enzymes functioning in different areas of fuel catabolism were measured under standardized conditions, using crude homogenates of sartorius and ventricular muscle from outbred guinea-pigs and rabbits indigenous to high or low altitude. The activities of sartorius and myocardium were found to reflect the metabolic patterns known to be associated with white and red muscle. Both species had right ventricular hypertrophy at high altitude. The enzyme activities in the high altitude guinea-pig were not significantly different from those in the sea level animals. In the high altitude rabbit, compared with the low altitude rabbit, the activities of glyceraldehyde-3-phosphate deydrogenase and phosphofructokinase were greater in both the sartorius and myocardium. In addition, mitochondrial glycerol-3-phosphate dehydrogenase activity was greater in the sartorius at high altitude, while aspartate aminotransferase and beta-hydroxyacylcoenzyme A dehydrogenase activities were greater in the myocardium at high altitude. Succinate dehydrogenase activity was comparable at the two altitudes for both tissues. There was a greater proportion of skeletal muscle type lactate dehydrogenase in the high altitude rabbit myocardium but no difference was found with the guinea-pig.

Alcohol Oxidoreductases↗
PubMed1990

Depression of posttetanic twitch potentiation by low calcium and calcium channel antagonists.

The purpose of this investigation was to determine if antagonizing extracellular calcium influx altered posttetanic twitch potentiation (PTP). Whole muscles and muscle fiber bundles (less than or equal to 25 fibers) dissected from frog sartorius and semitendinosus muscles were mounted at optimal length in a normal Ringer solution (NR). To determine PTP, isometric twitches were evoked every 10 s (0.1 Hz) before and after a 2.5-s tetanic contraction (80 Hz). To antagonize calcium influx, low-calcium Ringer [LCR, calcium replaced by 3 mM magnesium and 1 mM ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid], NR plus diltiazem (Dilt, 30 microM), NR plus nifedipine (Nif, 10 microM), and NR plus D 600 (30 microM) were also used (n = 8 for each condition). These conditions altered pretetanic twitch tension by only -1.2 +/- 2.4, 4.2 +/- 2.3, 4.7 +/- 3.7, and 1.6 +/- 3.7% (SE), (LCR, Dilt, Nif, and D 600, P greater than 0.05) but caused a noticeable decrease in tension at the end of the tetanus. Under NR conditions, twitches evoked immediately after the tetanus were potentiated by 49.5 +/- 0.4% with the peak rate of tension development (dP/dt) increased by 44.9 +/- 0.5% (P less than 0.05). Antagonizing calcium influx depressed the PTP response by 59.8 +/- 6.2, 55.9 +/- 10.1, 73.2 +/- 6.8, and 29.8 +/- 3.6% (P less than 0.05) and increased dP/dt by 65.8 +/- 11.1, 45.7 +/- 8.6, 55.6 +/- 4.4% and 49.0 +/- 10.5% (P less than 0.05). Addition of drugs immediately after the tetanus only slightly reduced PTP but accelerated recovery of the twitch.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1981

Effects of hyperosmotic solutions on the filament lattice of intact frog skeletal muscle.

The effect of increasing the osmotic strength of the extracellular solution on the fifament lattice of living frog sartorius and semitendinosus muscle has been studied using low-angle x-ray diffraction to measure the lattice spacing. As the extracellular osmotic strength is increased, the filament lattice shrinks like an osmometer until a minimal spacing between the thick filaments is reached. This minimal spacing varies from 20 to 31 nm, depending on the sarcomere length. Further increase in the osmotic strength produces little further shrinkage. The osmotic shrinkage curve indicates, for both muscles, an osmotically-inactive volume of approximately 30% of the volume in normal Ringer's solution. Shrinkage appears to be independent of temperature and the type of particle used to increase the osmotic strength (glucose, sucrose, small ions). The rate at which osmotic equilibruim is reached depends on muscle size, being slower for greater muscle diameters. Equilibrium spacings are approached exponentially with time constants ranging from 20 to 60 min. Independent of osmotic equilibrium, the lattice tends to shrink slowly by approximately 3% over the first few hours after dissection, probably because of a leakage of K+ ions from inside the muscle cells. This can be partly prevented by using an extracellular solution which contains a higher concentration of K+ ions or which is hypoosmotic. The volume of the muscle filament lattice (1.155d10(2) . S) is constant over a very wide range of sarcomere lengths, and is equal to approximately 3.6 x 10(6) nm3 for a range of amphibian muscle types.

Animals↗
PubMed1988

Proton spin-lattice relaxation time of Duchenne dystrophy skeletal muscle by magnetic resonance imaging.

By means of proton MRI, the spin-lattice relaxation times (T1 values) of pelvic and leg muscles were measured in Duchenne muscular dystrophy (DMD) patients and normal controls. The bound water fraction (BWF) was calculated from the T1 value obtained. In normal children, the T1 value decreased, and BWF increased with age. In DMD, the T1 value rapidly decreased, from an abnormally high value in the early stages, with the progress of the disease. This reduction of the T1 value in DMD was not the same for all muscles; it was most prominent in the gluteus maximus and least prominent in the sartorius and gracilis muscles. BWF was below normal in the early stages of DMD. It is suggested that both regenerating and degenerating muscle fibers, together with the increased muscle water content, cause the high T1 value and low BWF in the early stages of DMD, whereas replacement of muscle by fat causes the decreased T1 value in the advanced stages.

Child↗