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PubMed1987

The kinetics of heat production in response to active shortening in frog skeletal muscle.

1. Tension and heat production were measured at 0 degree C in sartorius muscles from Rana temporaria in response to two extents of shortening at five velocities. Shortening was from approximately 2.4 to 2.2 microns, 2.4 to 2.3 microns and 2.3 to 2.2 micron at velocities per half-sarcomere from 0.2 to 1.56 micron s-1. 2. Tension became approximately constant at all velocities. Records of heat rate obtained by differentiating traces from which thermoelastic heat had been subtracted became negative early in shortening and then rose. Heat rate became constant during shortening only at the lowest velocity and was still rising at the end of shortening at higher velocities. The highest heat rate occurred at the end of shortening at the two highest velocities. At the end of shortening at all velocities heat rate gradually approached the isometric level measured at the short length, the half-time for decline being largest following the slowest larger shortening. 3. Heat produced as a consequence of shortening but not associated with tension recovery was determined by subtracting shortening heat measured in response to two extents of shortening to the same muscle length. The differences in shortening heat continued to increase after shortening ended, and more of the extra heat produced in response to shortening appeared after the end of rapid shortening than during shortening itself. 4. Shortening heat coefficients calculated in different ways were similar to coefficients determined in previous studies. Coefficients calculated from measurements that excluded heat produced by tension recovery and allowed for continued production of heat by processes initiated by shortening were found to increase linearly with the force maintained during shortening. 5. The results show that the kinetics of heat production during and after shortening are very sensitive to the speed of shortening and that steady rates of energy liberation are not attained during shortening of less than or equal to 10% of muscle length at velocities greater than or equal to 12% of maximum velocity.

Animals↗

PubMed1978

Longitudinal pulse propagation characteristics in striated muscle.

The real part of the complex Young's modulus of whole frog sartorius muscle in the resting state was derived from step pulse propagation data in the frequency range 1.0-10 000 Hz. The derivation was based on Fourier integral analysis of the shapes of the propagated pulses to obtain velocities and attenuation coefficients for various harmonic frequencies. The results were consistent with previous sinusoidal wave propagation studies in the higher-frequency range. The general frequency response of the muscle was analogous to the "standard linear solid" model. The relaxation time spectrum derived from the modulus-frequency function showed similar spectral contents to spectra obtained with other methods. The advantages and limitations of the pulse method are discussed.

Acoustic Stimulation↗

PubMed1965

NONELECTROLYTE TRANSPORT IN MUSCLE DURING INDUCED PROTEIN LOSS.

The accelerated loss of protein from Rana pipiens sartorius muscle following the induction of rigor by 100 millimolar 1-pentanol is not accompanied by increase in the rate constant for the efflux of urea. This observation is not readily accounted for by classical lipid-pore membrane permeability models. Alternative models are considered, in which protein and nonelectrolyte transport are dissociated; the dissociation could be (i) topological, due to compartmentalization, or (ii) functional, for example, if protein loss were due to change of the state of intracellular protein or if urea transport were limited by diffusion in the cytoplasm.

Alcohols↗

PubMed1965

MUSCLE VOLUME CHANGES: RELATION TO THE ACTIVE STATE.

The volume of a frog sartorius muscle increases during a single twitch and subsequently decreases. The magnitude of volume change is 10(-5) cm(3) per gram of muscle. The time courses of change in volume and of onset of tension vary with temperature in a similar way, which implies a relation between the volume changes and the contraction mechanism. The character of the change depends upon the initial length of the muscle: the greatest decrease accompanies an isometric twitch at reference length. Treatment of the muscle with an iodide Ringer solution prolongs the active state and the volume change. These results suggest a correlation between the volume changes and the active state.

Animals↗

PubMed1988

Intracellular pH recovery from lactic acidosis of single skeletal muscle fibers.

Intracellular pH (pHi), measured with H+-selective microelectrodes, in quiescent frog sartorius muscle fibres was 7.29 +/- 0.09 (n = 13). Frog muscle fibres were superfused with a modified Ringer solution containing 30 mM HEPES buffer, at extracellular pH (pHo) 7.35. Intracellular pH decreased to 6.45 +/- 0.14 (n = 13) following replacement of 30 mM NaCl with sodium lactate (30 mM MES, pHo 6.20). Intracellular pH recovery, upon removal of external lactic acid, depended on the buffer concentration of the modified Ringer solution. The measured values of the pHi recovery rates was 0.06 +/- 0.01 delta pHi/min (n = 5) in 3 mM HEPES and was 0.18 +/- 0.06 delta pHi/min (n = 13) in 30 mM HEPES, pHo 7.35. The Na+-H+ exchange inhibitor amiloride (2 mM) slightly reduced pHi recovery rate. The results indicate that the net proton efflux from lactic acidotic frog skeletal muscle is mainly by lactic acid efflux and is limited by the transmembrane pH gradient which, in turn, depends on the extracellular buffer capacity in the diffusion limited space around the muscle fibres.

Acidosis, Lactic↗

PubMed1977

Chloride-induced contraction in a skinned fiber of toad striated muscle.

Cl- -induced contraction was studied in a skinned fiber dissected from toad sartorius muscle. When K-methanesulphonate in a relaxing solution was replaced isotonically with KCl, the skinned fiber contracted due to 'depolarization'-induced Ca++ release on the SR. Contraction was induced by superfusing the fiber with solutions containing different concentrations of Cl-. In the presence of 2 mM EGTA, the Cl- -induced contraction developed when the relaxing solution was replaced by a Cl- solution which contained up to 20 mM Cl-, while contraction started at 15 mM-Cl- in the presence of 0.5 mM EGTA. The peak tension of the Cl- -induced contraction depended on Cl- concentration without obeying the all-or-none law. When the fiber was treated with 1.5 mM caffeine, the threshold for the Cl- -induced contraction was significantly lowered. In spite of previous application of Cl- at different concentrations below 80 mM, the skinned fiber contracted by sudden increase in Cl- concentration, and the tension versus Cl- concentration curve revealed almost the same shape as that in a fiber equilibrated with Cl- -free solution. This suggests that the SR membrane is repolarized after transient depolarization caused by elevation of Cl- concentration.

Animals↗

PubMed1980

Apparent affinity changes induced by insulin of Na-K transport system in frog skeletal muscle.

The dependency of Na efflux on intracellular Na concentration was examined on sartorius muscles of Rana catesbeiana. In normal Ringer, the rate coefficient of 22Na efflux is nearly proportional to the internal Na concentration, i.e., Hill's coefficient in the dependency of Na efflux on internal Na concentration was around two. As long as insulin is present in the bathing solution, the rate coefficient of 22Na efflux retains the stimulated level. Insulin caused a leftward shift of the relationship between Na efflux and the logarithm of internal Na concentration, and concomitantly decreased Hill's coefficient. A model of the coupling of Na transport and hydrolysis of ATP was proposed. The theoretical relation derived from this model accounted for these findings quite satisfactorily. According to this model, insulin shifts as a cofactor the equilibrium between dephosphorylated and phosphorylated states of carriers, whose Na binding sites are not occupied by Na, toward the phosphorylated state.

Animals↗

PubMed1986

Kinetic investigation of K+ efflux during glycerol treatment of muscle.

The kinetics of K+ efflux was investigated in the membranes of frog sartorius muscle after disintegration by glycerol treatment. Data of the K+ concentration in the muscle as a function of time of the glycerol treatment fitted well the sum of two exponential fractions (with the correlation coefficient of more than 0.98). The half-lives of the two fractions of the K+ efflux were 1 and 75 hours respectively. On the basis of the value of its half life the efflux of the faster fraction was suggested to correspond to the free diffusion. At low temperature the magnitude of the faster fraction increased in a Na+-containing milieu. This could be due to K+-Na+ ion exchange. From the rate of loss of the slower fraction of K+ one finds that movement of K+ in cells without membranes is significantly slower than free diffusion. Presumably, part of the bound potassium exists in intra- or intermolecular "ion-bridges" of muscle proteins.

Animals↗

PubMedDate not supplied

[Intracellular local changes of resistance in muscle fibers in relation to membrane potential].

Intracellular local changes of resistance in sartorius muscle of the frog were investigated. The changes of resistance that were earlier shown to be located very near to the tip of the microelectrode appear in response to the changes of membrane potential evoked in various ways: polarization with electric current, depolarization with increase of the extracellular [K+], generation of action potentials. Depolarization leads to the local decrease of resistance, hyperpolarization--to increase of it. By using the tree-barreled microelectrodes with various geometry of the cross section, an attempt was undertaken to check some spatial peculiarities of the structure responsible for the local changes of resistance.

Action Potentials↗

PubMed1985

Norepinephrine depolarizes sartorius but hyperpolarizes soleus muscles in vitro.

Having previously found that in vivo administration of norepinephrine (NE) depolarizes the membrane of hamster sartorius muscle cells, the present study evaluated NE effects in vitro where alterations in blood flow were eliminated. Muscles were submerged in a temperature-controlled chamber, held at their resting length, and impaled with glass microelectrodes. Norepinephrine addition (maximum concentration of 10-20 microM at the muscle surface) induced significant depolarization in sartorius muscle cells and significant hyperpolarization in soleus muscle cells (P less than 0.05). Ascorbic acid (final concentration 15-25 microM), the vehicle for NE, evoked no significant alteration in resting membrane potentials of either muscle. Isoproterenol, a beta-adrenoceptor agonist, elicited responses similar to those of NE; phenylephrine, an alpha-adrenoceptor agonist, had no significant effect. The data suggest that the NE response is mediated through the beta-adrenergic pathway and that in the hamster, both hyperpolarization and depolarization can be observed under the same experimental conditions, depending on the muscle in question.

Adrenergic Agonists↗

PubMed1987

Comparative histochemistry of a flatfish fin muscle and of other vertebrate muscles used for ultrastructural studies.

Because of the high degree of filament order in the myofibrils of fish skeletal muscles, and the resulting usefulness of such preparations (particularly flatfish fin muscles) in structural studies of muscular contraction, the fibre type composition of plaice fin muscle has been determined by conventional histochemical tests. As controls, and for comparison, fibre type distributions have also been studied in several other vertebrate skeletal muscles which are widely used for ultrastructural and mechanical studies. In view of the importance of single fibres in such studies and because much of the published information on fibre types is rather difficult to collate, we summarize here the fibre compositions of several muscles; comparable enzyme tests have been carried out on cryostat sections of rabbit psoas muscle, frog sartorius and semitendinosus muscles and plaice fin muscles. On this basis all four muscles are composed of more than one fibre type. We confirm that frog sartorius muscle is mainly a random mixture of two fast fibre types and show that there is also a third group of fibres which are small, metabolically rich and dark under acid m-ATPase tests. We confirm that the semitendinosus is composed of three fibre types, in three non-exclusive, concentric regions and that rabbit psoas muscle contains a mixture of at least three fibre types. The principal new findings of this work are that plaice fin muscle can be divided into four regions, some of which are composed of more than one fibre type, on the basis of its histochemical reactions. This division into regions changes seasonally. The system of classification devised by Dubowitz & Brooke (1973) for mammalian muscle, and which can be applied approximately to frog muscle, can also be applied to the fibres of plaice fin muscle provided that the test for lactate dehydrogenase is carried out in the presence of polyvinyl alcohol. These fibres do not easily fit the division into red, white and intermediate types normally used for fish myotomal muscles. Since none of these muscles is homogeneous, their complex nature must be borne in mind if they are to be used satisfactorily in structural and mechanical studies of muscular contraction involving the use of single fibres.

Adenosine Triphosphatases↗

PubMed1982

The dual effect of rubidium ions on potassium efflux in depolarized frog skeletal muscle.

The effects of external Rb+ on the efflux of 42K+ from whole frog sartorius muscles loaded with 305 mM K+ and 120 mM Cl- were studied. K+ efflux is activated by [Rb+]o less than about 40 mM according to a sigmoid relation similar to that for activation by [K+]o. At [Rb+]o greater than 40 mM, K+ efflux declines, although at [Rb+]o = 300 mM it is still greater than at [Rb+]o = 0 mM. For low concentrations, the increment in K+ efflux over that in K+-and Rb+-free solution, delta K, is described by the relation delta k = a[X+]on, for both K+ and Rb+. The value of a is larger for Rb+ than for K+, while the values of n are similar; the activation produced by a given [Rb+]o is larger than that by an equal [K+]o for concentrations less than about 40 mM. Adding a small amount of Rb+ to a K+-containing solution has effects on K+ efflux which depend on [K+]o. At low [K+]o, adding Rb+ increases K+ efflux, the effect being greatest near [K+]o = 30 mM and declining at higher [K+]o; at [K+]o above 40 mM, addition of Rb+ decreases K+ efflux. At [K+]o above 75 mM, where K+ efflux is largely activated, Rb+ reduces K+ efflux by a factor b, described by the relation b = 1/(1+c[Rb+]o). Activation is discussed in terms of binding to at least two sites in the membrane, and the reduction in K+ efflux by Rb+ at high [K+]o in terms of association with an additional inhibitory site.

Animals↗

PubMed1976

Deuterium oxide effects on excitation-contraction coupling of skeletal muscle.

2H2O (99.8%) Ringer's solution greatly reduces the twitch and tetanus of frog sartorius muscle and, as specially shown here, slows the onset features of the mechanical output of the twitch by: (a) increasing the time (LR) from stimulus to start of latency relaxation; (b) slowing the development of the latency relaxation, and (c) greatly decreasing the rate of onset of tension development. These changes reflect effects of 2H2O on excitation-contraction coupling and they represent the critical direct effects of 2H2O on muscle since it does not depress either the action potential or the intrinsic myofibrillar contractility. The increase in LR is attributed to slowed inward electrical propagation in the T-tubule. But the critical effect of 2H2O on frog muscle is to greatly depress mobilization of activator Ca2+. The depression of the Ca2+ mobilization and of its effects on the activation of contraction evidently result from (a) a lowered rate of release of Ca2+ from the sar coplasmic reticulum, as indicated by the slowed development of the latency relaxation, (b) a decreased amount of Ca2+ released in a twitch, and (c) a reduced speed of diffusion of the Ca2+ to the contractile filaments. The depressed mobilization of Ca2+ is apparently the essential cause of 2H2O's general depression of twitch and tetanus output.

Animals↗

PubMed1959

Rubidium and cesium fluxes in muscle as related to the membrane potential.

The reduction of membrane potential in frog sartorius muscle produced by rubidium and cesium ions has been studied over a wide concentration range and compared with depolarization occasioned by potassium ions. The constant field theory of passive flux has been used to predict the potential changes observed. The potential data suggest certain permeability coefficient ratios and these are compared with ratios obtained from flux data using radioactive tracers. The agreement of the flux with the potential data is good if account is taken of the inhibition of potassium flux which occurs in the presence of rubidium and cesium ions. A high temperature dependence has been observed for cesium influx (Q(10) = 2.5) which is correlated with the observation that cesium ions depolarize very little at low temperatures. The observations suggest that cesium ions behave more like sodium ions at low temperatures and more like potassium ions at room temperature with respect to their effect on the muscle cell resting potential. The constant field theory of passive ion flux appears to be in general agreement with the experimental results observed if account is taken of the dependence of permeability coefficients on the concentrations of ions used and of possible interactions between the permeabilities of ions.

Animals↗

PubMed1967

Some relations between changes in the linear electrical properties of striated muscle fibers and changes in ultrastructure.

Some of the linear electrical properties of frog sartorius muscle have been investigated in Ringer's fluid and in a Ringer fluid made hypertonic by the addition of sucrose or NaCl. Electrical constants were determined from measurements of the phase angle of the admittance of a fiber for an applied alternating current, from measurements of the voltage induced by an inward pulse of current, and from measurements of the conduction velocity of the action potential and the time constant of its foot. The dilation of the transverse tubular system induced by the sucrose hypertonic Ringer fluid was correlated with the change in the electrical constants. From this it is concluded that a two time constant equivalent circuit for the membrane, as proposed by Falk and Fatt, is in good agreement with our results. Both the area of the membrane of the transverse tubular system, and the capacity (c(e)) attributed to it, increased in the sucrose hypertonic Ringer fluid. The resistance r(e), which is in series with c(e), did not fall when the transverse tubular system was dilated and probably is not located in that system.

Action Potentials↗

PubMed1976

Strophanthidin-sensitive sodium fluxes in metabolically poisoned frog skeletal muscle.

Strophanthidin-sensitive and insensitive unidirectional fluxes of Na were measured in fog sartorius muscles whose internal Na levels were elevated by overnight storage in the cold. ATP levels were lowered, and ADP levels raised, by metabolic poisoning with either 2,4-dinitrofluorobenzene or iodoacetamide. Strophanthidin-sensitive Na efflux and influx both increased after poisoning, while strophanthidin-insensitives fluxes did not. The increase in efflux did not require the presence of external K but was greatly attenuated when Li replaced Na as the major external cation. Membrane potential was not markedly altered by 2,4-dinitrofluorobenzene. These observations indicate that the sodium pump of frog skeletal muscle resembles that of squid giant axon and human erythrocyte in its ability to catalyze Na-Na exchange to an extent determined by intracellular ATP/ADP levels.

Adenosine Diphosphate↗

PubMed1959

The ineffectiveness of carnitine preventing the twitchings of striated frog muscle in 0.7 per cent sodium chloride solution.

The spontaneous twitchings of isolated frog sartorius muscles in 0.7% NaCl solution have been studied. Addition of 1 mg./ml. of (+/-)-carnitine hydrochloride, or of (+/-)-carnitine base, to the bath fluid had no influence on the spontaneous activity of the muscles, their excitability or their ability to liberate potassium. This indicates that carnitine is not a natural inhibitor of striated frog muscle. Fluids enriched with potassium either from twitching muscle or by addition of KCl inhibited the activity of muscles reversibly.

Animals↗

PubMed1971

The effects of ethacrynic acid and other sulphydryl reagents on sodium fluxes in frog muscle.

1. Ethacrynic acid (2 mM) increased the sodium efflux from freshly dissected frog sartorius muscles. This increase was not observed in muscles previously treated with strophanthidin.2. In strophanthidin-treated muscles, the addition of ethacrynic acid (2 mM) caused a reduction of sodium efflux. The value of efflux reached in these muscles is similar to that observed in muscles immersed in sodium-free solutions containing strophanthidin.3. Ethacrynic acid reduced sodium influx into strophanthidin-treated muscles. Potassium influx was not affected by this substance. These findings suggest that the inhibitor blocks an exchange of sodium for sodium.4. The increase in sodium efflux caused by ethacrynic acid did not result from depolarization nor from an increase in [Na](i).5. Ethacrynic acid caused only a reduction of sodium efflux in muscles previously loaded with sodium by prolonged immersion in potassium-free solutions at low temperatures.6. A derivative of ethacrynic acid that lacks the ability to combine with sulphydryl (SH) groups did not reduce sodium efflux from muscles treated with strophanthidin.7. Para-chloromercuribenzoic acid (PCMB) reduced sodium efflux from control and strophanthidin-treated muscles. This reduction seems to be restricted to the sodium dependent component of the efflux.8. The inhibition of the sodium-dependent component of sodium efflux caused by ethacrynic acid and PCMB appears to have a similar mechanism, namely, the combination with SH groups.

Animals↗