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At least 523 records · Page 29Linked to original sources

PubMed1989

Neuronal control of extrajunctional acetylcholine receptor-channels induced by injury in frog skeletal muscle fibres.

(1) Frog Sartorius muscles were transected to form two muscles: a neural segment (tibial part) containing all the endplates, and an aneural segment (pelvic part). The acetylcholine receptor-channels which appear at both new ends of the muscle fibres were studied by spectral analysis of membrane current fluctuations elicited by acetylcholine (ACh). (2) During the first two weeks after muscle transection, the ACh-receptors at the new muscle-tendon junction of the neural segment opened channels which had a long open time, similar to that of extrajunctional ACh-receptor channels induced by denervation of non-transected muscles. Subsequently, the open time of the new channels became shorter, and, about three weeks post-transection, it resembled that of channels at innervated endplates of normal muscles. The characteristics of the end-plate channels were not appreciably altered by the transection. (3) Similar results were observed when the muscle was crushed instead of being transected; and the change from slow to fast channel kinetics occurred earlier. (4) Denervation of neural segments prevented the change from slow to fast channel kinetics. The channels in the new muscle-tendon junction of the aneural segment remained slow up to three months post-transection. (5) These results indicate that the motor nerve controls the properties of the ACh-receptors induced by muscle transection.

Animals↗

PubMed1978

Caffeine contracture and iodoacetate rigor in frog skeletal muscle. A comparison.

Frog sartorius muscle treated with 5.0 mM or greater caffeine exhibits stiffness similar to that obtained from muscle in iodoacetate rigor. The data provide quantitative evidence that suggests that caffeine at irreversible contracture-producing concentrations somehow induces a rigor or rigorlike state in skeletal muscle.

Animals↗

PubMed1976

A reexamination of the thermoelastic effect in active striated muscle.

Isolated Rana pipiens sartorius muscles at 0degreeC were stimulated via their nerves and small stretches or releases applied during the plateau of the isometric tetanus at lo. Extra heat above the isometric maintenance heat was produced during the drop in tension caused by release and, for very small releases (delta less than or equal to 0.5% lo), was completely reabsorbed during tension recovery. The extra heat was always directly proportional to the tension change. Heat absorption proportional to the tension change was also observed during the increase in tension produced by small stretches in the range 0.5% lo less than or equal to deltal less than or equal to 3.0% lo. The mean heat:tension ratio R in seven experiments was -0.0084, which is within the range of values reported previously by Woledge. In addition, it was found that during tension recovery after small releases of 1.0% lo less than or equal to deltal less than or equal to 3.0% lo the "contractile" component seems able to shorten about 1% lo without producing shortening heat.

Animals↗

PubMed1982

Action of caffeine in excitation-contraction coupling of frog skeletal muscle fibres.

1. Frog sartorius muscle bathed in 1 mM-caffeine generates brief asynchronous contraction of individual sarcomeres, 'sarcomeric oscillations', and propagated contractile waves. 2. Analysis of cinematographic records shows that during sarcomeric oscillations the sarcomere length decreases and the distribution of sarcomere lengths is wider than in controls. 3. Caffeine can produce sarcomeric oscillations in K depolarized muscle fibres and, to a limited extent, in glycerol-treated muscle fibres. 4. Treatment of muscle with dantrolene sodium blocks production of sarcomeric oscillations by caffeine. 5. In caffeine-treated muscle fibres, electrically produced depolarization could initiate or increase the frequency of sarcomeric oscillations, and electrical hyperpolarization diminishes the frequency or stops sarcomeric oscillations. 6. Caffeine solution bathing a muscle undergoing sarcomeric oscillations (the perfusate), when applied to a fresh muscle, initiates sarcomeric oscillations with a relatively short latency. 7. An U.V.-absorbance peak at 245 nm develops in the caffeine solution bathing a muscle undergoing sarcomeric oscillations. 8. It was found that a contraction-regulating substance (oscillogen) is released from a muscle undergoing sarcomeric oscillations. From results of selective dialysis and gel permeation chromatography, the molecular weight of the oscillogen is estimated to be between 700-1000 daltons. 9. It is proposed that the oscillogen is a normally occurring substance which functions in excitation-contraction coupling at the T-tubule terminal cistern junction in skeletal muscle.

Animals↗

PubMed2004

A phenomenological model for estimating metabolic energy consumption in muscle contraction.

A phenomenological model for muscle energy consumption was developed and used in conjunction with a simple Hill-type model for muscle contraction. The model was used to address two questions. First, can an empirical model of muscle energetics accurately represent the total energetic behavior of frog muscle in isometric, isotonic, and isokinetic contractions? And second, how does such a model perform in a large-scale, multiple-muscle model of human walking? Four simulations were conducted with frog sartorius muscle under full excitation: an isometric contraction, a set of isotonic contractions with the muscle shortening a constant distance under various applied loads, a set of isotonic contractions with the muscle shortening over various distances under a constant load, and an isokinetic contraction in lengthening. The model calculations were evaluated against results of similar thermal in vitro experiments performed on frog sartorius muscle. The energetics model was then incorporated into a large-scale, multiple-muscle model of the human body for the purpose of predicting energy consumption during normal walking. The total energy estimated by the model accurately reflected the observed experimental behavior of frog muscle for an isometric contraction. The model also accurately reproduced the experimental behavior of frog muscle heat production under isotonic shortening and isokinetic lengthening conditions. The estimated rate of metabolic energy consumption for walking was 29% higher than the value typically obtained from gait measurements.

Animals↗

PubMed1979

The actions of 5-hydroxytryptamine on isolated skeletal muscle preparations.

The effects of 5-hydroxytryptamine (5HT) on the mouse phrenic nerve--hemidiaphragm and frog sartorius muscle preparations were studied using twitch tension and intracellular recording methods. Between 1--7.5 mM 5HT transiently augmented the twitch response of the diaphragm to indirect, but not direct, stimulation. Above 5 mM 5HT the augmentation was followed by a concentration-dependent twitch blockade. The blockade was more apparent in anticholinesterase-treated preparations, and was seen to a lesser extent in directly stimulated muscles. Intracellular recording from diaphragm muscles revealed that 5HT depressed the amplitudes of both miniature endplate potentials (m.e.p.p.s.) and endplate potentials (e.p.p.s.), this effect being more pronounced in the presence of neostigmine. 5HT also greatly prolonged the duration of the e.p.p.s. In the sartorius muscles, 1--5 mM 5HT slowed and depressed action potentials. It is suggested that 5HT facilitates transmission by an anticholinesterase action and inhibits by blockade of receptor ion channels.

Action Potentials↗

PubMed1983

The effect of cellular energy reserves and internal calcium ions on the potassium conductance in skeletal muscle of the frog.

The increase in K+ conductance induced by repetitive stimulation in metabolically poisoned sartorius muscle fibres of the frog was investigated, using a two-micro-electrode voltage-clamp technique. After the inhibition of creatine kinase by 0.4 mM-1-fluoro-2,4-dinitrobenzene (FDNB) and a complete and irreversible exhaustion of contractility, a nearly linear current-voltage relation was measured between -100 and 0 mV. In the presence of CN- (4 mM) an 'intermediate state' could be established by repetitive stimulation towards complete mechanical exhaustion. In this labile state, the high and potential-independent K+ conductance could be induced by repetitive voltage-clamp pulses (100 ms duration) from -85 to 0 mV membrane potential. After the pulses had ceased, fibres regained their original membrane conductance within several minutes. After the electrophoretic injection of the Ca2+-chelating agent H2EGTA2- into fibres in the intermediate state, an increase in membrane conductance by repetitive voltage-clamp pulses could no longer be induced. Fibres in the intermediate state into which H2EGTA2- -buffered Ca2+ (free Ca2+ approximately 10(-5) M) was injected, or to which external caffeine (1.5 mM) was applied, showed a spontaneous and reversible increase in membrane conductance. In metabolically poisoned and mechanically exhausted sartorius muscles the concentrations of creatine phosphate (CP) and ATP were estimated using biochemical standard methods. The concentration of CP remained basically unchanged after FDNB poisoning. In solutions containing CN- plus iodoacetate CP fell below the detectable concentration of about 0.5-1% of the normal value. ATP decreased to slightly less than 20% under both conditions. It is concluded that internal free Ca2+ promotes the activation of the K+ conductance in exhausted muscle fibres, and that a shortage of energy reserves increases the 'sensitivity' of K+ channels to Ca2+ ions.

Adenosine Triphosphate↗

PubMed1990

Microvascular response to ischemia, and tissue structure, in normal and atrophied skeletal muscle.

The objective of this study was to explain why the normally observed reactive hyperemia in frog sartorius muscle following ischemia is absent when this muscle atrophies. Two possibilities were addressed: (1) absence is due to lowered O2 consumption, making the muscle more tolerant to ischemia, and (2) absence is linked to impaired vascular function in atrophy. We used 10 frogs after 2-3 months and 8 frogs after 7-14 months of laboratory captivity. Animals in the latter group had a significantly lower sartorius muscle weight, i.e., 85 +/- 33 vs 24 +/- 11 SD mg. Using intravital video microscopy, we measured red cell velocity in capillaries at the muscle surface, and densities of capillaries with moving (NCPER) and stationary red cells (NCSTAT) before and after 30 min ischemia. Ischemia induced a significant temporary increase in overall velocity (from 0.10 to 0.27 mm/sec) in normal muscles, but no increase in atrophied muscles. It resulted in no difference in NCPER between the two groups (preischemic levels in both groups: 15.0 cap/mm of test line), but in a significant difference in NCSTAT (3.8 vs 11.5 cap/mm in atrophy). Using light and electron microscopy, we also measured structural and ultrastructural parameters in both groups. In atrophied muscles the mean fiber cross-sectional area was lower (568 vs 1935 microns 2) and anatomical capillary density higher (892 vs 282 cap/mm2) than in normal muscles. Mitochondrial volume density was not statistically different from the 1.5% level in the normal muscle, while the lipid droplet volume density was larger (2.33 vs 0.58%). The percentage of capillaries with damaged endothelium was larger (33.5 vs 12.6%). Using histology, the white cell volume density per capillary volume was also found to be larger in atrophy (1.96 vs 0.83%). From the discrepancy between the lack of intergroup difference in preischemic NCPER and the 3.2-fold difference in anatomical capillary density we estimate that about 60% of capillaries were perfused with red cells in atrophied muscles. Although the preischemic rate of perfusion in these capillaries was comparable between the two groups, the postischemic response was not: reactive hyperemia was absent in atrophy. Our mitochondrial and lipid volume density data do not support the possibility that this absence was due to lowered O2 consumption, as these densities did not decrease with atrophy.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1980

[Electrical and cholinoreceptive properties of muscle fiber membranes following blockade of axoplasmic transport by colchicine].

The electrical properties and acetylcholine sensitivity in frog sartorius muscle fibres were investigated after denervation and after single application of colchicine to the nerve. Similar changes followed both kinds of the nerve injury. No changes developed in the contralateral sartorius muscle. The injection of colchicine into the lymphatic sac of the frog induced extrasynaptic acetylcholine sensitivity but did not change the electrical properties of the membrane. The data obtained are considered as additional suggestion for the role of exoplasmatic transport of materials in the denervation changes in muscle if excitation transmission is intact.

Acetylcholine↗

PubMed1983

Effects of kava on neuromuscular transmission and muscle contractility.

The effects of kava, a native drink from Oceania, on neuromuscular transmission and muscle contractility have been examined in mouse phrenic nerve-hemidiaphragm and frog sartorius muscle preparations using twitch tension and intracellular recording techniques. The extent of muscle paralysis induced by kava was similar in both directly and indirectly stimulated mouse hemidiaphragms. The neuromuscular blockade produced was poorly reversed by calcium and by neostigmine. Intracellular recordings from frog sartorius muscles showed that kava depressed the amplitude of both miniature end-plate potentials (mepps) and end-plate potentials (epps) but had no effect on the frequency of mepps. Kava greatly prolonged the duration of mepps and epps and also slowed and depressed directly elicited muscle action potentials. It is concluded that kava causes paralysis by mechanisms similar to local anaesthetics.

Action Potentials↗

PubMed1989

Organ culture of frog muscle: maintenance of mass, enzyme levels, and contractile force.

This paper describes an organ culture system that maintains frog sartorius muscles in good condition for 5 days. In the absence of serum and insulin, muscles maintained at approximately 93% of resting length atrophied with significant decreases in dry weight, protein content, and contractile force, and in the levels of activity of citrate synthase, lactate dehydrogenase, and creatine kinase. Inclusion of 1.0 mU/ml of insulin in the culture medium prevented the decreases in muscle mass, twitch tension, and citrate synthase activity and minimized the decreases in lactate dehydrogenase, creatine kinase, and tetanic tension. Inclusion of 10% serum, in addition to 1 mU/ml insulin, in the medium did not have clear cut additional benefits. Stretching muscles to 110% of resting length (L0) resulted in marked deterioration with decreases in total protein, enzyme levels, and contractile force. Keeping muscles at approximately 93% L0 was as effective as maintenance at L0 in preventing atrophy and loss of contractile force and enzyme activities. This organ culture procedure, which maintains frog sartorius muscle in good condition without serum for at least 5 days, may provide a useful model for studying the regulatory mechanisms responsible for a variety of adaptations in muscle.

Animals↗

PubMed1975

Structural dynamics of frog muscle during isometric contraction.

Intensity fluctuation autocorrelation functions of laser light scattered by actively contracting muscle were measured at points in the scattered field. They were reproducible and showed characteristics which depended on the physiological state of the muscle and the parameters of the scattering geometry. The autocorrelation functions had large amplitudes and decay rates that varied significantly with the phase of the contraction-relaxation cycle. The dependence of the autocorrelation function on scattering geometry indicated many elements with diameters on the order of 0.5 mum (presumed to be myofibrillar sarcomeres or their A bands or I bands) undergo independent random changes in their axial positions and their internal distribution of optical polarizability during the plateau of an isometric tetanus. The experimental results are interpreted in terms of a model in which most of the scattering elements in isometrically contracting muscle have random fluctuating axial velocities of average magnitude 20 nm/ms that persist for a few milliseconds at least. In addition to these axial motions there are local fluctuations in polarizability. Similar intensity fluctuation autocorrelation functions were observed throughout the active state on two muscle preparations, whole sartorius muscle and small bundles of single fibers (three to eight) of semitendinosus muscle. These results imply that the tension developed during an isometric tetanus contains a fluctuating component as well as a constant component.

Animals↗

PubMed1975

Sizes of components in frog skeletal muscle measured by methods of stereology.

Stereological techniques of point and intersection counting were used to measure morphological parameters from light and electron micrographs of frog skeletal muscle. Results for sartorius muscle are as follows: myofibrils comprise 83% of fiber volume; their surface to volume ratio is 3.8 mum-1. Mitochondria comprise 1.6% of fiber volume. Transverse tubules comprise 0.32% of fiber volume, and their surface area per volume of fiber is 0.22 mum-1. Terminal cisternae of the sarcoplasmic reticulum comprise 4.1% of fiber volume; their surface area per volume of fiber is 0.54 mum-1. Longitudinal sarcoplasmic reticullum comprises 5.0% of fiber volume, and its surface area per volume of fiber is 1.48 mum-1. Longitudinal bridges between terminal cisternae on either side of a Z disk were observed infrequently; they make up only 0.035% of fiber volume and their surface area per volume of fiber is 0.009 mum-1. T-SR junction occurs over 67% of the surface of transverse tubules and over 27% of the surface of terminal cisternae. The surface to volume ratio of the caveolae is 48 mum-1; caveolae may increase the sarcolemmal surface area by 47%. Essentially the same results were obtained from semitendinosus fibers.

Animals↗

PubMed1998

Effects of varied fatigue protocols on sarcoplasmic reticulum calcium uptake and release rates.

The purpose of this investigation was to examine changes in sarcoplasmic reticulum (SR) function in muscles subjected to different patterns of muscle activity. Frog sartorius muscles were stimulated with tetanic trains (100 ms, 100 Hz) delivered at rates of 2.0, 0.5, and 0.2 trains/s. In one set of experiments, stimulation was continued until force had declined to approximately 17% of initial (constant fatigue), whereas in the other set, stimulation was continued for 1 min (constant duration). In the constant-fatigue experiments, Ca2+ uptake (1 mM MgATP) and release rates (25 microM AgNO3, 5 mM 4-chloro-m-cresol) were depressed by similar extents following each protocol. This occurred despite 1, 4, and 17 min of stimulation, respectively, used to induce fatigue. In the constant-duration experiments, larger reductions in SR function occurred following the highest frequency stimulation protocol. These data suggest that when muscles are fatigued to similar extents, depressions in SR function are independent of the activity protocol. On the other hand, when a constant duration of activity is imposed, changes in SR function are closely linked to the extent of force reduction.

Adenosine Triphosphate↗

PubMed2003

MR findings of spinal muscular atrophy Type II: sibling cases.

We present magnetic resonance (MR) findings of siblings affected by spinal muscular atrophy (SMA) Type II. MRI of their thighs showed severe muscle atrophy and fatty infiltration. Selective preservation of the adductor longus muscle, the gracilis muscle, and the sartorius muscles was observed, suggesting a characteristic finding of SMA Type II. These findings were more severe in the older patient.

Child, Preschool↗

PubMedDate not supplied

[Functional properties of fragments of the sarcoplasmic reticulum of the fast and slow muscles of Rana ridibunda frogs].

It has been demonstrated that fragmented sarcoplasmic reticulum (FSR) from slow rectus abdominis muscle exhibits lower Ca/ATP ratio, lower Ca2+ uptake and higher Ca2+ release from the vesicles as compared to the reticulum from fast sartorius muscle. The rate of Ca2+ uptake by sartorius muscle is equal to 4.78, that by rectus abdominis muscle -- to 2.90 muM/min/mg of protein. The value of Km for the release of calcium from FSR of rectus abdominis muscle is equal to 1.25-10(-5)M, of sartotius muscle -- to 2.5-10(-5)M. Therefore, sarcoplasmic reticulum of the abdominal muscle exhibits lower capacity to retain the accumulated calcium.

Adenosine Triphosphatases↗

PubMed1995

Dynamic myoplasty in growing dogs as a feasibility study for treatment of fecal incontinence.

The feasibility of skeletal muscle transposition and electrical stimulation (dynamic myoplasty) for treatment of fecal incontinence has been shown in adults. It might be attractive to use such a technique in pediatric patients. Therefore, the influence of growth on skeletal muscle transposition and stimulation was studied in five puppies. In each dog, two neosphincters were constructed around a Thiry-Vella loop by using a dissected sartorius muscle with the neurovascular supply intact. In each of these five puppies, one of these muscles was electrically stimulated during a mean of 19 weeks (one puppy died during the first postoperative week). Muscle biopsies showed an increase in the percentage type I, fatigue-resistant muscle fibers from 61 to 94 in electrically stimulated sartorius neosphincters, but also an increase from 57 to 67 percent in transposed nonstimulated sartorius muscles. The diameter of these type I fibers during growth increased 36% in eletrically stimulated sartorius neosphincters and 55% in nonstimulated sphincters. Function of the neosphincters was tested with the inflow of saline in the Thiry-Vella loop. It was shown that the stimulated neosphincters were capable of inhibiting flow (which corresponded to manometric pressure registrations), but the nonstimulated sphincters were unable to inhibit flow. The experiments were complicated by infection and necrosis around the implanted stimulators in four puppies (which required reimplantation). We conclude that a dynamic myoplasty for fecal incontinence is feasible in growing puppies but that the technique is unacceptable during rapid growth because of the risks of infection and dislocation of the implanted device.

Anal Canal↗

PubMed1996

Influence of increasing breast meat yield on muscle histology and meat quality in the chicken.

The histological characteristics, ie, myofibre types and cross-sectional areas (CSA), of pectoralis major and sartorius muscles of 20 male chickens from two lines (ten birds from each line) divergently selected for breast meat yield were compared. Moreover, some quality parameters (ie, drip loss, ultimate pH value and meat colour) of the breast muscle were recorded. The animals from both lines displayed identical pectoralis major myofibre types and CSA. A slight difference in typology, but not in myofibre CSA, was observed in the sartorius muscle: animals with the highest breast meat yield tended to have a more pronounced glycolytic character. No significant difference was observed in the quality of breast meat (pH, colour and drip loss).

Animals↗