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PubMed2000

Role of volume-conductor properties of muscles in the formation of evoked contractions during stimulating electrical impedance myography.

Experiments on the preparation of frog sartorius muscle showed that electrical impedance myogram of evoked muscle contractions is the sum of electric processes accompanying contraction of some muscle fibers or muscle regions. Inverted muscle response probably results from heterotopic excitation of distant muscle regions under conditions of reduced excitability of muscle fibers adjacent to the electrode. During centrifugal propagation of contractions, especially in altered muscles, the negative wave on the myogram corresponding to impedance decrease is sometimes followed by a positive wave. The possibility for recording of heterotopic contractions indicates that the impedance of the electrode-muscle interface produces no considerable effects on the shape of electrical impedance myogram. These results hold much promise for the diagnostics of neuromuscular diseases.

Animals↗

PubMed1984

Blockade of electrophysiological properties of muscle fibres by lycorine.

This study concerns the action of the alkaloid lycorine on electrophysiological properties of single sartorius muscle fibres. Lycorine caused a decrease of the resting membrane potential, a lengthening in the rise and decay times of the action potential and a fall of the muscle accommodation. The depolarizing effect was not affected when Na+ is replaced by choline in the Ringer solution. Lycorine did not inhibit the (Na+ + K+) ATPase activity. The results suggest that action of lycorine on the electrophysiological properties can be attributed to an interference with potassium channels.

Action Potentials↗

PubMed1977

Prenylamine-induced contracture of frog skeletal muscle.

1. Experiments were performed to determine the influence of prenylamine on excitation-contraction coupling in frog sartorius muscle. 2. Prenylamine (0.2-1.0 mM) produced a biphasic contracture in skeletal muscle characterized by an initial phasic and subsequent tonic contracture. 3. Neither dantrolene nor procaine blocked the prenylamine-induced contracture. Pretreatment with 100 mM K+ blocked the phasic but not the tonic component of the prenylamine contracture. 4. Prenylamine produced a sustained increase in 45Ca efflux at all concentrations that produce contracture. These concentrations of prenylamine also depressed the action potential, muscle twitch and resting potential. 5. Low concentrations of prenylamine (0.05 mM) which produced neither contracture, 45Ca efflux nor 45Ca influx, depressed the action potential, muscle twitch and K+ contracture. 6. The results suggest that prenylamine not only alters calcium mobility but also membrane permeability to other ions.

Action Potentials↗

PubMed1975

Light scattering associated with tension changes in the short-range elastic component of resting frog's muscle.

1. A study has been made of some optical and associated mechanical properties of resting frog's sartorius muscles in isotonic and hypertonic solutions. Tension and transparency changes accompanying small alterations of muscle length (smaller than 1-5%) were recorded simultaneously. 2. The form of the transparency change is complex. It has three phases, two of which occur during the length change and the third (delayed phase) after it is complete. Directional recording of the response reveals both scattering and diffraction components. 3. The change of light scattering is associated with tension changes in the short-range elastic component (SREC) of the muscle. Its magnitude is related to the stiffness of the SREC; both increase when the osmotic strength of the external solution is raised and when muscle length is increased. 4. The change of light scattering is not much affected by the velocity of the applied length change. This is true also of the mechanical stiffness of the SREC. 5. The origin of the diffraction change is not known. 6. It is concluded that the scattering effect is caused by conformational changes in the SREC.

Animals↗

PubMed1982

Active groups of saxitoxin and tetrodotoxin as deduced from actions of saxitoxin analogues on frog muscle and squid axon.

1. The actions of three saxitoxin (STX) analogues have been studied on the frog sartorius muscle fibre and the squid giant axon. One--neosaxitoxin--is a natural analogue, and two--decarbamylsaxitoxin and reduced saxitoxin--are synthetic. 2. The maximum dV/dt of the action potential in paired-muscle protocol is reduced by the analogues with relative potencies: STX (1), tetrodotoxin (1), neo-STX (1), decarbamyl-STX (0.2) and reduced-STX (0.01). 3. In constant-current studies on frog muscle fibres and in voltage-clamp studies on squid axons, all three analogues block only the sodium channel without affecting the potassium channel. 4. All three analogues bind to the same site as does STX in a competitive manner. 5. The experimental results suggest that the active groups in STX are the 7,8,9 guanidinium and the C-12 hydroxy groups. The carbamyl group contributes to, but is not essential for activity. 6. Stereospecific groups in the tetrodotoxin (TTX) molecule are the 1,2,3 guanidinium and the C-9, C-10 hydroxy groups. C-4 and C-8 groups are also important. 7. As new view is proposed in which STX and TTX can bind to a receptor located in the outside surface of the membrane very close to the orifice of the sodium channel.

Action Potentials↗

PubMed1983

Aequorin-calcium transients in frog twitch muscle fibres.

Intracellular Ca2+ transients, evoked either by action potentials or depolarizing clamp pulses, were studied in frog sartorius muscle fibres injected with aequorin. The time course of the Ca2+ transients became shorter as the temperature was increased. The half rise time and decay time constants showed straight lines between 3 and 30 degrees C in Arrhenius plots, with a Q10 of 2.5 and 2.3 respectively. The potential dependence of the Ca2+ transient was examined under voltage clamp. The peak light amplitude reached a plateau at around +50 mV, suggesting that Ca2+ release continues beyond the potential level at which contraction was saturated. During a prolonged depolarization, the Ca2+ transient gradually declined. The time course of decline became faster when long depolarizing pulses were repeated, or when the temperature was increased. The Q10 for half duration of the Ca2+ transient evoked by prolonged depolarization was 2.2. A Ca2+ transient could be evoked in Ca2+-free Ringer solution containing EGTA. Formamide, which is known to abolish excitation-contraction coupling, also abolished the Ca2+ transient. During maintained depolarization, the time integral of the Ca2+ transient was larger for larger depolarizations, suggesting that the total amount of Ca2+ released was greater for the more intense depolarization. The decline of the Ca2+ transient during maintained depolarization is probably due to inactivation of excitation-contraction coupling rather than the depletion of intracellular Ca2+ stores. These findings support the view that in frog skeletal muscle fibres the increase in intracellular Ca2+, caused by membrane depolarization, is produced by the release of Ca2+ from intracellular stores and that any influx of Ca2+ from the external medium does not contribute appreciably to the aequorin-Ca2+ transient.

Action Potentials↗

PubMed1982

Magnesium increases rate of onset of desensitization in frog muscle.

The effect of changes in extracellular and intracellular magnesium content on desensitization rate in frog (Rana pipiens) sartorius muscle was studied using measurements of input conductance of single fibers during local superperfusion of the postjunctional region with carbamylcholine chloride (0.27-2.7 mM). Two intracellular KCl-filled glass capillary microelectrodes were used for current injection and recording in fibers equilibrated in high-K+ media (33-165 mM). In low-ionic strength solutions (33 mM K), time to half-decline of conductance during desensitization to carbamylcholine (T1/2) was decreased by increasing extracellular Mg2+ concentration throughout range 0-100 mM. Equivalent effects on T1/2 were produced by increased extracellular Ca2+ in lower concentrations (0-10 mM). Increase in K+ concentration or decrease of carbamylcholine concentration resulted in increased T1/2 in both Mg2+ and Ca2+ media. Increase of intracellular Mg2+ by soaking in high-Mg2+ solutions (100 mM) or by intracellular iontophoresis caused decrease in T1/2. It is concluded that Mg2+, when introduced either in the extracellular or intracellular phase, can promote increased desensitization rate and that this action is similar to but weaker than that of calcium.

Animals↗

PubMed1975

Influence of ammonium ions on mechanical and electrophysiological responses of skeletal muscle.

Substitution of ammonium ions for sodium ion initially potentiated and then depressed twitch tension of the frog sartorius muscle. The extent of potentiation and the rate of depression of the twitch were dependent upon the concentration of ammonium ions. Ammonium ion depolarized individual muscle fibers in proportion to concentration. Maximum depolarization (33 mV) occurred in muscles equilibrated in 120 mM ammonium-Ringer for 30 min. At the higher concentration of ammonium (72--120 mM), the potentiation was quickly reversed and the tension response was eliminated completely. The gradual loss of twitch tension was accompanied by progressive decrease in the electrical excitability of individual muscle fibers. Raising the extracellular calcium concentration fivefold reduced the twitch-depressant effect of ammonium ions by maintaining excitability of the muscle fibers. Caffeine contractures (3 and 10 mM) in muscles preequilibrated in 72 mM ammonium-Ringer developed similar tensions to paired controls muscles, but the onset of tension was more rapid in the ammonium-treated muscle. It was concluded that the depression of tension could be accounted for by the loss of membrane excitability and that the evidence did not support the hypothesis that ammonium ions acted at other sites in the excitation contraction coupling.

Animals↗

PubMed1980

The interaction between the effects of insulin and ouabain on the activity of Na transport system in frog skeletal muscle.

The effects of insulin and ouabain on 22Na efflux and net Na loss were examined in frog sartorius muscles. After removal of ouabain, 22Na efflux which had been inhibited by ouabain remained at the inhibited level for more than 2 hr. In ouabain-free solution, insulin stimulated the Na efflux from ouabain-preincubated muscles. The stimulating effect of insulin on 22Na efflux was completely blocked by the presence of ouabain. Insulin shifted the Na efflux vs. intracellular Na concentration relationship toward the region of lower Na concentrations, and made the slope of log (Na efflux) vs. log [Na]1 relationship less step. On the other hand, ouabain shifted the Na efflux vs. intracellular Na concentration relationship toward the region of higher Na concentration, and made the slope of the log (Na efflux) vs. log [Na]1 relationship steeper. The relationship between insulin-stimulated Na efflux and intracellular Na concentration obtained from ouabain-preincubated muscle was located in the region of higher Na concentrations than that obtained from control muscle. These findings suggest that insulin increases an apparent affinity of binding sites for Na ions, and the possibility that insulin increases the Vmax of Na transport system may be excluded. In contrast with the effect of insulin, ouabain may be considered to decrease the apparent affinity of binding site for Na ions.

Animals↗

PubMed1965

THE POTASSIUM FLUX RATIO IN SKELETAL MUSCLE AS A TEST FOR INDEPENDENT ION MOVEMENT.

The flux ratio of potassium ions was measured on frog sartorius muscle under conditions in which a substantial net potassium loss occurs. Muscle fiber membrane potentials were measured under identical conditions. The observed flux ratios were compared with values calculated from a theoretical relation derived on the assumptions that the unidirectional fluxes are both passive and occur independently. The results favor the conclusion that the potassium fluxes across skeletal muscle membrane occur along passive electrochemical gradients and obey the independence principle.

Animals↗

PubMedDate not supplied

[Relation between the intensity of low-angle equatorial reflections of x-ray diffraction patterns of frog skeletal muscle and sarcomere length].

Dependence of the intensities of low-angle equatorial reflections from frog live resting sartorius muscle on sarcomere length between 1.95 micron and 3.1 micron were studied in stretch and shortening regimes. It is found that intensities of the (10), (20), (30) and Z-reflections increase at sarcomere length increase from about 2 micron, reach maximum value at sarcomere length between 2.3 micron and 2.7 micron, and then fall at further increase of the sarcomere length. The (11) and (21) intensities decrease at sarcomere length increase. A conclusion is drawn that tetragonal lattice of the thin filaments near Z-line gives essential contribution to Z-reflection together with Z-line. It is proposed that hexagonal lattice of A-band and tetragonal lattice of the thin filaments distort each other at sarcomere length less than 2.3 micron and have the most order at sarcomere length between 2.3 micron and 2.7 micron. At further increase of the sarcomere length the packing of both lattices deteriorates apparently due to other factors than in the case of the short sarcomere length.

Animals↗

PubMed1981

[Effect of protein synthesis inhibitors on D-xylose transport in frog muscle tissue].

The action of puromycin and cycloheximide on the uptake of D-xylose in isolated frog sartorius muscles has been studied. Cycloheximide and puromycin were found to stimulate the basal transport of xylose and to inhibit the insulin-stimulated sugar uptake. On the other hand, both these antibiotics did not affect the sugar transport stimulated by 2,4-dinitrophenol. Both of them, even at a high concentration (up to 0.1 mg/ml), inhibited the incorporation of leucine or valine into muscle proteins by 50% only, whereas they did inhibit the sugar transport at a concentration much lesser by several orders. The inhibitors of protein synthesis are supposed to affect directly the signal transmission from insulin receptors to the sugar transport system.

Animals↗

PubMed1985

Reappraisal of diffusion, solubility, and consumption of oxygen in frog skeletal muscle, with applications to muscle energy balance.

Previously we tested the validity of the one-dimensional diffusion equation for O2 in the excised frog sartorius muscle and used it to measure the diffusion coefficient (D) for O2 in this muscle and the time course of its rate of O2 consumption (Qo2) after a tetanus (Mahler, 1978, 1979, J. Gen. Physiol., 71:533-557, 559-580, 73:159-174). A transverse section of the frog sartorius is in fact well fit by a hemi-ellipse with width divided by maximum thickness averaging 5.1 +/- 0.2. Using the previous techniques with the two-dimensional diffusion equation and this hemi-elliptical boundary yields a value for D that is 30% smaller than reported previously; the revised values at 0, 10, and 22.8 degrees C are 6.2, 7.9, and 10.8 X 10(-6) cm2/s, respectively. After a tetanus at 20 degrees C, Qo2 rose quickly to a peak and then declined exponentially, with a time constant (tau) approximately 15% faster than that reported previously; tau averaged 2.1 min in Rana temporaria and 2.6 min in Rana pipiens. A technique was devised to measure the solubility (alpha) of O2 in intact, respiring muscles, and yielded alpha (muscle)/alpha (H2O) = 1.26 +/- 0.04. With these modifications, the values for O2 consumption obtained with the diffusion method were in agreement with those measured by the direct method of Kushmerick and Paul (1976, J. Physiol. [Lond.]., 254:693-709). Using results from both methods, at 20 degrees C the ratio of phosphorylcreatine split during a tetanus to O2 consumption during recovery ranged from 5.2 to 6.2 mumol/mumol, and postcontractile ATP hydrolysis was estimated to be 13.6 +/- 4.1 (n = 3) nmol/mumol total creatine.

Adenosine Triphosphate↗

PubMed1988

Use of selective toxins to separate surface and tubular sodium currents in frog skeletal muscle fibers.

The interaction between toxin gamma from the venom of the scorpion Tityus serrulatus and sodium channels in skeletal muscle membranes from the frog Caudiverbera caudiverbera was studied. Sodium current from cut sartorius muscle fibers is a complex signal in which early and late components are difficult to separate. External application of Tityus gamma toxin initially blocked the early component in a voltage-dependent manner. Longer exposure to the toxin induced a complete blockade of the two components of the inward current. Application of tetrodotoxin to fibers pretreated with Tityus toxin at submaximal concentrations allowed the observation of the two distinct components of the inward current. Binding of 125I-labelled toxin to highly purified membrane fractions from the same muscle was used to establish the presence of high affinity receptors both in the transverse-tubular and in the surface membrane.

Animals↗

PubMed1986

Observation of the terminal methyl group in fatty acids of the linolenic series by a new 1H NMR pulse sequence providing spectral editing and solvent suppression. Application to excised frog muscle and rat brain.

A new 1H NMR pulse sequence is described that combines water suppression with the selective observation of signals from coupled spin systems. The pulse sequence is easy to set up and compensates for pulse width inhomogeneity in the biological sample. Suppression of the water signal is achieved by pulses that return the water spins to their equilibrium position; spectral editing is based on the J modulation present in spin-echo spectra and its inhibition by coherent decoupling at one of the resonances of the spin system of interest. The pulse sequence, which was designed for 1H NMR spectroscopy of tissue, was tested at 470 MHz on excised frog muscle and rat brain. The lactate methyl resonance of caffeine-treated frog sartorius muscle was observed selectively by irradiation at the position of its alcoholic proton. The terminal methyl signal of linolenic acid, along with other fatty acids of the linolenic series (first double bond in the omega-3 position), was observed selectively by irradiation at the position of its omega-1 methylene group. 1H NMR spectra of rat brain were edited to reveal the terminal methyl of either linolenic series or all other fatty acids. The results suggest that the terminal methyl groups of fatty acids of the linolenic series (mostly docosahexaenoic acid, 22:6) have higher mobility than those of all other fatty acids.

Animals↗

PubMed1990

Detection and isolation of a 30 kDa abnormal protein in avian dystrophic muscle.

We have studied the protein composition of the pectoralis superficialis muscle of genetically dystrophic (New Hampshire line 413) and normal control (line 412) chickens by one- and two-dimensional gel electrophoresis. A protein, referred to hereafter as the 30 kDa abnormal protein, was specifically detected in the affected muscle. It was purified to homogeneity, and its molecular properties were studied. It is a monomer with a molecular mass of approximately 30 kDa and an isoelectric point of about pI 8.4. We have screened by Western blotting a variety of muscles from line 412 and line 413 chickens for the presence of the 30 kDa protein. While the pattern of total protein is very similar in all cases, the 30 kDa protein was not detected in the pectoralis superficialis muscle of line 412 chickens. However, the immunoreactive bands were detected in the sartorius muscle and the tensor fasciae latae muscle from dystrophic and normal chickens. Interestingly, the immunoreactive bands of normal skeletal muscles are smaller in molecular weight than those of dystrophic skeletal muscles. To determine the early time sequence of the appearance of the abnormal protein, we studied muscles from embryos and post-hatched chickens at various ages. The abnormal protein was detected in dystrophic muscles as early as 15 days ex ovo and occurred throughout development up to six months ex ovo. Although the implication of the dystrophy-associated appearance of the 30 kDa protein in the affected muscle is not clear at present, it would be of particular interest to elucidate the biochemical functions of the 30 kDa protein in the affected muscle (pectoralis superficialis muscle) of genetically dystrophic chicken.

Animals↗

PubMed1977

Frog muscle spindles with unbranched myelinated afferent axons: the response to stretch and the length of the first myelinated segment.

1. Twenty-five muscle spindles innervated by unbranched myelinated axons in the capsule were isolated from sartorius muscle in young frogs (2-2--9-5 g in weight, 28-47 mm in rostro-caudal length). 2. The lengths and the diameters of the first myelinated segments varied from 30 to 170 mum and from 9 to 20 mum respectively. There was no relationship between the lengths and the diameters. 3. Dynamic and static components were analysed from discharge rates of the muscle spindles during ramp-and-hold stretches of 0-8 mm from different initial lengths. The values of the dynamic components to a certain stretch stimulation increased with shortening in the length of the first myelinated segment. The values of the static components were independent in length. 4. The amplitudes of action potentials recorded from the spindle terminal decreased during the dynamic phase of the stretch. The ratio of amplitude decrease at the end of the dynamic phase versus the initial length depended upon the length of the first myelinated segment. 5. These results suggest that the discharges during stretch may arise at the first node, though the spontaneous discharges may be generated at the terminal.

Action Potentials↗

PubMed1983

Kinetic properties of calcium channels of twitch muscle fibres of the frog.

Calcium currents (ICa) were recorded in frog skeletal muscle fibres using the three-micro-electrode voltage-clamp technique. The sartorius muscle was bathed in TEA methanesulphonate saline with 350 mM-sucrose. 5 mM-3,4-diaminopyridine was added to the saline to minimize K+ currents. The I-V relationship for peak Ca2+ currents showed that ICa was detected at -40 mV and reached a maximum value at ca. -10 mV. No net inward current was recorded at potentials positive to ca. +40 mV. Remaining K+ currents (IK) were recorded by replacing 10 mM-Ca2+ with 5.5 mM-Co2+. They were not noticeably time-dependent up to +20 mV and would tend to diminish the amplitude of ICa without greatly affecting its time course. ICa tail currents could be separated from non-linear capacity currents. Tail currents were measured 5 msec after repolarization and extrapolated to the end of the pulse. ICa tail-current amplitudes at EK were measured with pulses of different durations. The envelope of tail-current amplitudes declined with a time course similar or identical to that of inward current during a maintained depolarization. Consequently, the decline of inward current cannot be explained by an increase of outward IK with time. ICa inactivated with 9 sec prepulses which did not elicit detectable ICa. The fitted h infinity curve had a mid point of -33.0 mV and a steepness of 6.3 mV. ICa between -30 mV and +20 mV could be described adequately using the Hodgkin-Huxley m3h relationship. The fitted m infinity curve had a mid point of -35.2 mV and a steepness of 9.9 mV. The limiting Ca2+ permeability PCa was 1.4 +/- 0.4 X 10(-4) cm/sec.

4-Aminopyridine↗