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PubMed1982

The influence of voltage conditioning on chloride currents in amphibian muscle membrane: the sigmoid conductance-voltage relation extended into the outward current region.

Sartorius muscle fibres of Xenopus laevis were depolarized in solutions of high K+ content and then voltage clamped in solutions in which K+ was replaced by Rb+ and(or) tetraethylammonium ion (TEA+) at pH 9. A three-microelectrode clamp system was used in which the bath was held at virtual ground using an operational amplifier in a current meter configuration. The holding potential was set at zero membrane current potential (resting potential), close to -25 mV. A two-pulse paradigm was used to test the effects of conditioning the membrane at voltages away from the resting potential on initial currents at positive test potentials. In the absence of TEA+ rapidly rising outward currents were generated at positive test potentials, following hyperpolarizing conditioning. These currents inactivated in time and obscured predicted chloride currents. When TEA+ was added to the solution (60 mequiv./L) the currents at positive potentials rose more slowly and declined either very slowly or not at all. Projection of these current waveforms, by curve fitting, to the instant of potential change gave a sigmoid dependence of test current on conditioning voltage that was predicted from earlier results. Predictably there is a test voltage at which the initial current is independent of conditioning potential: from the data it appears that this is not necessarily the resting potential, but the cause of the shift is not clear. The results also indicated that there is a component of outward current that is very small, apparently carried by cations ("delayed rectifier current"), that does not inactivate, even at potentials more positive than the resting potential.

Animals↗

PubMed1984

Measurement of the lineal density of red blood cells in capillaries in vivo, using a computerized frame-by-frame analysis of video images.

In order to study the oxygen supply system within a capillary bed it is desirable to know the lineal density of red blood cells (RBCs) in individual capillaries; viz number of cells per millimeter. We have developed a video computer method for "continuous" measurements of lineal density, based on frame-by-frame analysis of the spatial-average of blood opacity over a selected length of capillary. Each capillary is calibrated separately, in order to determine the relationship between mean opacity and lineal density for that vessel. Since the method does not attempt to detect individual RBCs, it can be applied to capillaries with RBCs which overlap each other to some extent. Also, since the opacity data is normalized with respect to "background" light intensity and "contrast," this technique can be applied to thick tissues such as skeletal muscle. The method has been tested on capillaries in frog sartorius muscle and is able to predict, on average, the number of frog RBCs in an 80-micron length of capillary to +/- one-quarter cell. At present, computation times limit "real time" measurement of lineal density to a sampling rate of 10 sec-1. The data may also be used (1) to compute red cell flux (cells X sec-1), if corresponding velocity measurements are available, and (2) to estimate capillary hematocrit.

Animals↗

PubMed1986

Mechanical properties of denervated amphibian muscle.

Denervated amphibian muscle does not show the prolongation of action potential found in mammalian denervated muscle. It was, therefore, predicted that denervated amphibian muscle would not show prolongation of the mechanical twitch. The sartorius muscles in one leg of toads--Xenopus borealis--were denervated for 140-268 days. Isometric twitch time to peak, time to half relaxation and twitch/tetanus ratio were not changed following denervation, confirming our prediction. Twitch tension decreased to 68% and tetanic tension decreased to 75% of control values. The maximum velocity of unloaded shortening (muscle length/s) was also unchanged.

Action Potentials↗

PubMed1983

Immunoelectron microscopic studies of desmin (skeletin) localization and intermediate filament organization in chicken skeletal muscle.

We studied the localization of desmin (skeletin), the major subunit of muscle-type intermediate filaments, by high resolution immunoelectron microscopy in adult chicken skeletal muscle. Immunoferritin labeling of ultrathin frozen sections of intact fixed sartorius muscle showed the presence of desmin between adjacent Z-bands and as strands peripheral to Z-bands, forming apparent connections between the Z-bands with adjacent sarcolemma, mitochondria, and nuclei. We observed no desmin labeling, however, in the vicinity of the T-tubules. In addition, intermediate filaments were morphologically discernible at the level of the Z-bands in plastic sections of glycerol-extracted muscle that had been infused with unlabeled antidesmin antibodies. Our results indicate that the desmin present in adult skeletal muscle, that had previously been detected by immunofluorescence light microscopy, is largely if not entirely in the form of intermediate filaments. The results provide evidence that these filaments serve to interconnect myofibrils at the level of their Z-bands, and to connect Z-bands with other specific structures and organelles in the myotube, but not with the T-tubule system.

Animals↗

PubMed1975

Actions of a new muscle relaxant (AH8165) on neuromuscular transmission.

The effects of a new muscle relaxant, AH8165, on miniature endplate potential (MEPP) amplitude and frequency, endplate sensitivity to acetylcholine, and muscle twitch tension were studied in vitro in the frog sartorius muscle. Nerve terminal effects were studied in vivo in the cat soleus muscle and its ventral root fibers. AH8165 stimulates the nerve terminal, as evidenced by increased MEPP frequency and the appearance of post-drug repetitive activity. In the same concentration range at which MEPP frequency is increased, MEPP amplitude, endplate sensitivity to acetylcholine, and twitch tension are decreased. This suggests that AH8165 produces muscle relaxation by blocking postsynaptic cholinergic receptors. (Key works: Neuromuscular relaxants, AH8165.).

Acetylcholine↗

PubMed1989

[One mechanical property of contraction of isolated bullfrog geniohyoid muscle].

In general, skeletal muscle activity has been understood on the basis that the muscle is functionally consisted of contractile element and elastic element. In this paper it has been attempted to clarify the specific role of the geniohyoid muscle which is one member of the oro-basal muscular system, because our previous reports suggested an elastic specificity of only this muscle as supposed, for example, from the presence of posttetanic twitch attenuation under isotonic condition. For this reason, the experiments have been carried out with paying attention to an interrelationship between loading and contraction figure. When the geniohyoid muscle, weighing over 320 mg, was contracted without any loading, downward undulation under the base line (abbreviated by negative deflection) could be obviously seen within the period succeeding after a falling or relaxation phase of a contraction curve. This negative deflection which presumably indicates the elastic behavior disappeared with increasing the loads from nothing to 4 times the muscle weight. This 3-4 times loading was peculiar to the geniohyoid muscle. In the same situation, 4-5 times loading was specific to the rectus abdominis muscle, and 7-8 times loading was specific to the sartorius muscle. Furthermore, when the geniohyoid muscle was divided first to 1/2 and then to 1/4, the negative deflection of each muscle block was shifted to the lighter side of the applied load. Additional experimental results will be accumulated in the next report.

Animals↗

PubMed1989

[The action of ketamine on muscle contractile behavior. In vitro studies on the musculature of subjects susceptible to malignant hyperthermia].

Since ketamine has been incriminated as triggering malignant hyperthermia (MH) [3, 9, 13, 14, 18], but has still been used uneventfully in MH susceptible patients, we performed an in vitro study to examine the safety of ketamine for use in human MH. METHODS. Muscle specimens of 20 patients who had muscle biopsies to diagnose MH were investigated. In every patient diagnostic contracture tests (2 halothane (Hal) and 2 caffeine (Caf) were done according to the protocol established by the European MH group (EMHG). In addition, one test unit for investigating the effect of stepwise increased bath-concentrations of ketamine (5, 10, 20, 60, 120, 240 and 960 mumol/l) and a further one serving as control (no drugs added to the bath) were used. Combined Hal (2 vol%) and Ket (960 mumol/l) tests were performed in 9 patients (4 MHS, 4 MHN, 1 MHEh). Changes in baseline contractures and mechanical twitch tension were evaluated. RESULTS. The diagnostic test showed MHS in 8, MHN in 8 and MHEh in 4 patients. Ketamine did not induce baseline contractures in any of the tests performed. Contractures induced by 2 vol% of halothane in 4 MHS muscles did not change significantly when ketamine was added to the bath (concentration 960 mumol/l). A significant, dose-related decrease in mechanical twitch tension occurred, when ketamine was added to the test. At the highest concentration (960 mumol) twitch tension was reduced by 55%. Twitch tension remained stable in untreated muscles. No significant differences were found between the specimens from MHS, MHN and MHE patients. This reduction in twitch tension was more pronounced in specimens exposed to both halothane (2 vol%) and ketamine (960 mumol/l), resulting in an average decrease of 71%. CONCLUSION. In accordance with Fletcher et al., our results indicate that ketamine - at least in vitro - does not trigger MH. In MHS muscles, ketamine does not augment halothane-induced baseline contractures. The ketamine-induced reduction of mechanical twitch tension in directly stimulated human muscles has not been described before. Analogous findings in frog sartorius muscles can be found in the literature. Whereas the effect of ketamine on indirectly stimulated muscle has been investigated by several authors, the underlying mechanism of ketamine-induced twitch suppression in directly stimulated muscles is not known. Inhibition of calcium release from or accelerated uptake into the sarcoplasmatic reticulum have been reported.

Caffeine↗

PubMed1978

Regulation of skeletal muscle development by the central nervous system in the fetal pig.

The effect of upper motor neuron regulation on skeletal muscle development was studied in the fetal pig. A region of the spinal cord at the level of the upper cervical vertebrae was destroyed by cauterization at 45 days of gestation in four pig fetuses. Five fetuses with intact spinal cords served as controls. Innervation and enzyme activities in the longissimus muscle, the ultrastructure and quantitation of satellite cells in the sartorius muscle, and plasma composition were evaluated at 110 days of gestation. The terminal innervation ratios were similar (P greater than 0.05) for muscles from control and cauterized fetuses. Endplate morphology was also similar. Therefore, innervation of newly formed primary fibers is not controlled by upper motor neurons after 45 days of gestation. Mean values for body weight, percentage of muscle dry weight, percentage of myofibers with myonuclei and plasma levels of protein, glucose, triglycerides, lactate, and creatine phosphokinase activity were similar (P greater than 0.05) between the two groups of fetuses. All but one muscle fiber examined was of the secondary fiber type. These observations suggest that the physiological maturity of the muscle was not appreciably altered even though glucose-6-phosphate dehydrogenase activity was higher (P greater than 0.05) and total phosphorylase activity was lower (P greater than 0.05) in the spinal cauterized fetuses than in the control group. The percentage of satellite cells was lower when based on the number of myofibers observed (P greater than 0.005) or on the number of nuclei contained within the basal lamina (P greater than 0.001) in the muscle of the spinal cauterized fetuses than in the control fetuses. The cytoplasm of satellite cells from the muscles of control fetuses was rich in organelles indicative of metabolic and mitotic activity whereas a paucity of such organelles was observed in the satellite cells of cauterized fetuses. Since the percentage of myofibers that had myonuclei was similar (P greater than 0.05) for the control and cauterized fetuses, it appeared that the myonuclear population was maintained by direct incorporation of the parent satellite cell.

Animals↗

PubMed1995

The influence of skeletal muscle incubation medium on fatigue of neuromuscular preparation and on transmitter release at neuromuscular junctions in the frog.

The effect of frog skeletal muscle incubate on fatigue was studied in frog sciatic nerve, sartorius muscle preparation. Fatigue was produced by prolonged repetitive (1 s-1) stimulation of motor nerve or of curarized muscle. The incubate partially restored isometric contraction amplitudes of muscle fatigued by nerve stimulation. This effect of partial recovery from fatigue (PRF effect) was exerted mainly by a relatively low-molecular fraction (LMF; < 10 kDa) of the incubate. The incubate and its fractions failed to produce the PRF effect in experiments with directly stimulated muscle. The action of LMF on synaptic transmission in unfatigued cutaneous-pectoris muscle was examined using binomial analysis of quantal transmitter release. LMF produced an increase in the end-plate potential quantal content (m) at synapses with low initial m values. In contrast, it produced a decrease i n m at synapses with higher m values. Both effects were due to respective changes in binomial parameter n. It is assumed that the stimulatory presynaptic action of the incubate on synapses the effectiveness of which was lowered during fatigue, could account for the PRF effect. A possible contribution of low- and high-molecular components of the incubate is discussed.

Animals↗

PubMed2000

Influence of dietary fat and vitamin E supplementation on free radical production and on lipid and protein oxidation in turkey muscle extracts.

The objectives of this study were to investigate the effects of dietary fat (6% soy oil or rapeseed oil or tallow) and alpha-tocopheryl acetate supplementation at two levels (30 or 200 ppm) on radical production, measured by ESR spectroscopy, and on lipid and protein oxidation in turkey muscle extracts oxidized by an enzymic system (NADPH, ADP, FeSO(4)/cytochrome P450 reductase). Two muscles were tested: pectoralis major (glycolytic) and sartorius (oxidative) muscles. Radical production measured by ESR was higher in pectoralis major muscle than in sartorius muscle, whereas lipid and protein oxidation was more important in sartorius muscle, showing the importance of the pro-/antioxidant ratio in oxidative processes in muscular cells and of the measurement methodology to appreciate the free radical production. Dietary fat had no effect on the level of ESR signals, whereas feeding of animals with soy oil induced higher oxidation of lipids. Protein oxidation was less sensitive to the nature of the dietary fat than lipid oxidation. Vitamin E supplementation significantly decreased radical production, as measured by ESR spectroscopy. Vitamin E also decreased lipid and protein oxidation, but the effect of vitamin E on protein oxidation was less pronounced than on lipid oxidation.

Animals↗

PubMed1983

Synaptic efficacy at singly- and dually-innervated neuromuscular junctions in the frog, Rana pipiens.

Electrophysiological investigation was performed on excised, curarized cutaneous pectoris and sartorius muscles of the frog. Sixteen percent of cutaneous pectoris and 7% of sartorius end-plates received dual innervation from two different axons. The resting membrane potential and input resistance of muscle fibers at single synapses were similar to those at dual junctions. The e.p.p.s. generated by individual axons in dual synapses were, on average, smaller in amplitude than e.p.p.s recorded from singly-innervated junctions. However, the total e.p.p. amplitude (sum of the two component e.p.p.s) at dually-innervated end-plates was similar to that of end-plates innervated by a single axon. Our results at polyneuronally-innervated end-plates are consistent with a model of simple competition between motor axons for a limited synaptic space.

Animals↗

PubMed1980

A model of myosin crossbridge structure consistent with the low-angle x-ray diffraction pattern of vertebrate muscle.

Low-angle X-ray diffraction patterns have been taken of relaxed frog sartorius muscles stretched to destroy the lattice sampling in the pattern and the observed layer line pattern has been interpreted with model-building studies. The modelling calculations indicate that each crossbridge cannot be represented by a single cylindrical shape, but that the two S-1 heads of the crossbridge are tilted in opposite directions along the filament while twisted the same way round it so that the crossbridge lies wrapped round the filament backbone. The radial position derived for the crossbridge depends on how many strands the filament is assumed to have. If the filament is 2, 3 or 4 stranded then the centre of mass of the crossbridge lies at about 9.5, 12.5, or 15.5 nm respectively from the filament axis.

Actins↗

PubMed1976

X-ray diffraction of actively shortening muscle.

Low angle x-ray diffraction patterns were obtained from resting and activated frog sartorius muscles by means of a position-sensitive detector. Although the intensity ratio I10/I11 decreased many-fold upon activation, it was nearly the same during isometric and isotonic contraction. Thus, motion has a much smaller effect on the low order equatorial pattern than the transition from rest to activity. Analysis of the 10 and 11 reflections separately showed that I10 and I11 change reciprocally upon activation, and that they both increase by a small amount in the transition from isometric to isotonic contraction. If the intensity ratio can be taken as a measure of cross-bridge number, the results provide evidence that the drop in force in an actively shortening muscle is due primarily to the influence of motion on the configuration, rather than the number, of cross-bridges.

Animals↗

PubMed1967

Enhanced permeability to sugar associated with muscle contraction. Studies of the role of Ca++.

When contractures were induced in isolated frog sartorius muscles with 4 mM caffeine, there was an increase in permeability of the muscle cells to 3-methylglucose. This observation suggests that the changes in permeability to sugar that are known to occur in electrically stimulated muscles may not be intimately related to the depolarization phase of the tissue response. Contractures that were elicited by exposing the muscles to a high concentration of K+ were also associated with an increased permeability to sugar. As the concentration of 45Ca in the medium was raised, more 45Ca entered the muscles during potassium contractures, and the contractures lasted longer, in agreement with the observations of other investigators. There was also a greater change in permeability to sugar when potassium contractures were elicited in the presence of higher concentrations of Ca++. The possibility that the enhanced permeability to sugar may be related to changes in the intracellular concentration of Ca++ is discussed.

3-O-Methylglucose↗

PubMed1967

The effect of low ionic strength extracellular solutions on the resting potential in skeletal muscle fibers.

Intracellular measurements of the resting potential were made in fibers of the frog sartorius muscle in solutions of varying salt composition and concentration to determine the effects of low ionic strength extracellular solutions on the resting potential. Changes in the glass microelectrode tip potential in low ionic strength solutions were minimized by adding ThCl(4) to the extracellular solution. These experimental conditions allowed measurement of the relationship of the resting potential to the concentration of the salt in the extracellular solution by replacing it with the nonionic substance, sucrose. Substitution of sucrose for the extracellular NaCl produced a stable depolarization which was logarithmically related to the NaCl concentration. Substitution of sucrose for choline Cl, instead of NaCl, produced the same degree of depolarization. When Na salts of anions less permeable than chloride (Br, I, NO(3)) were used, the resting potentials in 116 mM solutions were close to those with chloride (+/-3mv). The depolarizations produced in low ionic strength solutions of these salts were significantly less than those with chloride.

Animals↗

PubMed1957

Metabolic and other effects of reserpine upon smooth and skeletal muscle.

Reserpine increased the concentration of potassium ions in the fluid bathing the isolated frog sartorius muscle. The effect of reserpine upon respiration and upon glycolysis in rabbit intestinal muscle has been investigated using the Warburg "Direct" method. After a latent period, reserpine (50 mug./ml.) depressed respiration but did not affect glycolysis in gut muscle. These results, together with previous observations, may point to an effect of reserpine upon carbohydrate metabolism.

Animals↗

PubMed1983

Indifference of the resting potential of frog muscle cells to external Mg++ in the face of high Mg++ permeability.

Incubation of frog sartorius muscles for 18 hours at constant external concentrations of K+ and Na+, but with the external concentration of Mg++ varying from 1.2 to 73.2 mM, brought about no change in the resting potential which remained constant at 88 mV. Results were the same in MgCl2 as in MgSO4. However, these cells are nearly as permeable to Mg++ as they are to K+. These results contradict the membrane theory of the cellular potential but are compatible with the surface adsorption model of the cellular potential.

Animals↗

PubMed1992

Effects of N-ethylmaleimide on the structure of skinned frog skeletal muscles.

The effects of N-ethylmaleimide (NEM) and other sulfhydryl modifiers on the structure of skinned frog skeletal muscles were studied using the X-ray diffraction technique. In sartorius muscle with full overlap between the thick and thin filaments, 0.1-1.0 mM NEM changed the intensity ratio of the (1,0) and (1,1) equatorial reflections from 4.35 to 0.72, and the (1,0) spacing of the hexagonal filament lattice from 40.4 to 41.4 nm. The axial X-ray diffraction pattern showed weak myosin layer-lines after the NEM treatment but enhancement of the actin layer-lines was not observed. In overstretched semitendinosus muscle, NEM did not affect the equatorial spacing but the myosin layer-lines were weakened. These results indicate that modification of myosin by NEM destroys the helical arrangement of myosin heads around the shaft of the thick filament and that when thin filaments are available, myosin heads move towards, and possibly bind to them. This binding is different from that in rigor since the 'ladder-like' appearance of the higher actin layer-lines, which is typical of patterns from rigor muscles, was not observed. On removal of ATP after the NEM treatment, the diffraction pattern showed features characteristic of that from normal rigor muscles but no tension was produced. The pattern showed well-defined samplings on layer-lines in the small-angle region, indicating the presence of an extensive lattice order and exact axial alignment of the filaments. The first actin layer-line did not show samplings from the superlattice of the thick filaments, which are observed on the myosin layer-lines in patterns from resting muscles.(ABSTRACT TRUNCATED AT 250 WORDS)

Actin Cytoskeleton↗