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PubMed1980

Effects of amphotericin B on the electrical properties and electrolyte content of frog sartorius muscle.

We studied the effect of amphotericin B (52 microM) on the membrane potential, membrane resistance, and intracellular Na+ and K+ concentrations in isolated frog sartorius muscles to characterize further the nature of the ionic conductance induced by the antibiotic. After 5 h of exposure to amphotericin B, the membrane depolarized from -89.9 to -51.0 mV, the membrane resistance decreased from 4537 to 907 omega cm2, [K]i decreased from 122 to 31.2 mmol/L fiber H2O, and [Na]i increased from 30.9 to 88.7 mmol/L fiber H2O. The relative sodium permeability, PNa/PK, calculated with the Goldman equation remained apparently constant at a value of 0.01 in treated and untreated muscles. We hypothesize that amphotericin B creates either a nonselective cation channel or a completely nonselective ionic leak channel whose equilibrium potential is equal or close to the membrane potential.

Amphotericin B↗
PubMed1981

Effect of oxygen on arteriolar dimensions and blood flow in cat sartorius muscle.

The effect of O2 on arteriolar internal diameter, dual-slit velocity, and volume flow was studied by intravital microscopy in isolated autoperfused cat sartorius muscle. The muscle surface was covered with silicone oil, and gas mixtures containing 0, 5, 10, or 20% O2 in N2 were introduced over the muscle. When the O2 concentration was increased from 0 to 10%, arteriolar diameter, dual-slit velocity, and volume flow decreased on the average by 11 +/- 4, 30 +/- 29, and 37 +/- 13%, respectively. Under 20% O2, these parameters decrease by an additional 9 +/- 5, 29 +/- 10, and 30 +/- 14%, respectively. Percentage reduction in the diameter of large and small arterioles located at the same depth in the muscle were not significantly different. Conversely, the fall in volume flow was significantly greater in small arterioles. The lesser flow decrease in large vessels may reflect the fact that large vessels also feed deep muscle layers where the change in tissue O2 tension (PO2) is less. Our results do not support the hypothesis that small arterioles are intrinsically more sensitive to changes in tissue PO2.

Animals↗
PubMed1987

[The single nerve ending of the frog sartorius muscle: its ultrastructural characteristics and mediator secretion].

Electron microscopy and extracellular recordings were used for the investigation of structural and functional peculiarities of single frog sartorius muscle nerve terminal. It has been found that the diameter, length of the synaptic contact and quantity of synaptic vesicles decreased from proximal to distal parts of the nerve terminal. A number of varicosities, separated from each other by schwann cells, have been revealed along the course of the nerve terminal. This indicates the existence of an interrupted synaptic contact. Both the evoked and spontaneous transmitter release decreased from the initial to the end parts of the nerve terminal. The data obtained suggest that there is a correlation between structural heterogeneity and the differences in the transmitter release.

Animals↗
PubMed1973

Equilibrium of nucleotides in frog sartorius muscle during an isometric tetanus at 20 degrees C.

1. The concentrations of creatine, phosphorylcreatine (PC), ATP, ADP, AMP and IMP have been measured in frog sartorius muscles at 20 degrees C during isometric tetani lasting from 0.5 to 12 sec. Each muscle was tetanized once only for the chosen duration. The muscles were poisoned with iodoacetic acid and nitrogen to prevent oxidative and glycolytic activity.2. The rate of PC splitting decreased exponentially with the duration of the tetanus (alpha = 0.16 sec(-1)). Net ATP splitting began after 2 sec, accompanied by an increase in AMP and ADP; inosine monophosphate (IMP) also appeared both earlier and faster than adenosine monophosphate (AMP).3. On the basis of two equilibrium reactions, the Lohmann and myokinase reactions, the concentration of adenosine nucleotides should be a function of the ratio creatine/phosphorylcreatine.4. The agreement between nucleotide concentrations predicted by this equilibrium hypothesis and those observed experimentally was good provided it was assumed that 90% of the acid-labile ADP found in resting muscle was bound in vivo and remained so throughout the tetanus. The validity of this assumption is discussed.5. The IMP concentration was an exponential function of the ratio creatine/phosphorylcreatine.

Adenine Nucleotides↗
PubMed1995

Effect of tolbutamide on the rate of fatigue and recovery in frog sartorius muscle.

The goal of this study was to determine how blocking ATP-sensitive K+ channels with tolbutamide affects the excitability and contractility of intact frog sartorius muscle during fatigue development. Fatigue was elicited with one tetanic contraction every sec for 3 min. During fatigue the resting potential decreased by 10 mV although the action potential overshoot remained constant. The addition of 2 mmol.liter-1 tolbutamide 60 min before fatigue did not modify the effect of fatigue on the resting potential and action potential overshoot. During fatigue development the half-repolarization time of control muscles increased by 0.26 msec in control muscles, although it increased by 0.77 msec in the presence of 2 mmol.liter-1 tolbutamide; the difference was significant. The decrease in force during fatigue development was not affected by 2 mmol.liter-1 tolbutamide (added 60 min before fatigue), whereas the recovery of force after fatigue was slower in tolbutamide- exposed muscles than in control muscles. Addition of 2 mmol.liter-1 tolbutamide after 5 min of recovery reduced the recovery rate of the resting potential and half-repolarization time, but did not affect the recovery of tetanic force during the first 40 min. Our results are consistent with the hypothesis that ATP-sensitive K+ channels are activated during fatigue development and that they contribute to the repolarization phase of action potentials, but they do not support the hypothesis that ATP-sensitive K+ channels contribute to the decrease in force.

Action Potentials↗
PubMed1972

Heat production and fluorescence changes of toad sartorius muscle during aerobic recovery after a short tetanus.

1. The time course of the aerobic recovery following a 0.5 sec tetanus at 20 degrees C of the sartorius muscle of the toad Bufo bufo, equilibrated in bicarbonate-CO(2) Ringer solution, has been followed by recording simultaneously the heat production and the fluorescence excited by ultra-violet light at 366 nm.2. The fluorescence light emitted in these conditions in the region of 450 nm monitors the state of oxidation-reduction of the nicotinamideadenine dinucleotides (NAD(+)-NADH). After a short tetanus, the cycle evoked consists of an initial increase of the fluorescence (reduction of NAD(+)) followed by a long lasting phase of decreased light emission. This includes an early period of oxidation of NADH succeeded by a slow reduction of the NAD(+) formed in excess over the resting state. After iodoacetate, the initial reduction is suppressed.3. The time course of both fluorescence and heat production may be analysed into a rapid and a slow component by a double exponential model.4. The time courses of the aerobic recovery heat and of the fluorescence changes are similar after five minutes, but differ in their fast components. IAA significantly increases the rate constants of the fast terms of both monitors.5. The slow component is mainly related to aerobic processes while the fast one is due to both oxidative and glycolytic reactions occurring simultaneously.

Aerobiosis↗
PubMed1990

Series elasticity in frog sartorius muscle subjected to stretch-shortening cycles.

Changes in stiffness during stretch-shortening cycles were studied by applying prestretches of different rates and amplitudes on the tetanized sartorius muscle of the frog and measuring series elastic component characteristics during a subsequent quick release. Series elastic component stiffness was found to be dependent on the mechanical parameters of the stretching phase, and the so-called 'Cavagna effect' (increase in compliance) was rarely observed. The results are discussed in terms of improvement in muscle efficiency. Thus, an increase in stiffness during force generation will favour a better transmission of force and will reduce the coupling time whereas the opposite evolution during SEC recoil will allow a better release of potential energy.

Animals↗
PubMed1973

Energy balance in frog sartorius muscle during an isometric tetanus at 20 degrees C.

1. Changes in the concentrations of ATP, ADP, AMP, IMP, creatine and phosphorylcreatine (PC) have been measured in frog sartorius muscles after different periods of isometric stimulation at 20 degrees C. The heat production was measured in parallel experiments with a thermopile of the Hill-Downing type.2. Muscles were either in O(2) and unpoisoned or in N(2) and poisoned with iodoacetic acid to prevent aerobic and glycolytic recovery processes.3. Poisoning did not appear to alter the heat production of these muscles and had little effect on the tension for up to 8 sec tetanus.4. The break-down of high-energy phosphates ( approximately P) during contraction was faster in the poisoned muscles. Normal muscles were thus able to resynthesize high energy phosphates during the contraction. The resynthesis began at its maximum rate; part of it was probably due to glycolytic activity.5. During the first 2 sec of contraction (poisoned muscles), the only net reaction was an hydrolysis of PC, with an apparent enthalpy change of -8.3 kcal/mole. During longer contractions, the PC hydrolysis was accompanied by a net ATP hydrolysis and appearance of AMP and IMP.6. For the first 2 sec of contraction in the poisoned muscles, the observed heat agreed with that expected from the observed chemical changes multiplied by their molar enthalpy changes. After 2 sec, the observed heat was greater than that expected. At 12 sec this excess was about 74 mcal/g. Possible explanations for this discrepancy are discussed.

Adenine Nucleotides↗
PubMed1975

[Transport of D-xylose in isolated frog sartorius muscle in the presence of actinomycin D].

The action of actinomycin D on the basal and insulin stimulated D-xylose uptake has been studied on isolated frog sartorius muscles. Actinomycin D at concentrations of 10 mg/ml or 100 mg/ml exerts no effect on the basal transport of sugar and causes no alteration in the response to insulin. The distribution coefficient of actinomycin D in muscle tissue is equal 0,9--1. It is supposed that the inhibition of RNA synthesis by antibiotics does not influence sugar transport.

Animals↗
PubMed1976

Intracellular pH of frog sartorius muscle.

A weak base, morpholine, has been labelled with 3H and tested for its suitability as an indicator for intracellular pH, by distribution in the tissue water of frog sartorius muscle in the species Hyla litoria. Its pK'a at 20 degrees C in a solution of the same ionic strength as frog Ringer was found to be 8.45 +/- 0.02, which is in the range of maximal sensitivity. Morpholine equilibrated with the tissue in 17 h; it was shown that it was not bound to intracellular constituents, that it was not metabolised nor toxic in the concentrations used; it was therefore judged suitable as a pH indcator. Intracellular pH was then measured by distribution of morpholine (6.985 +/- 0.08), nicotine (6.915 +/- 0.03) and the weak acid 5,5'-dimethyl-2,4-oxazolidinedione (7.10 +/- 0.05) and the pH-sensitive microelectrodes (5.9, the equilibrium value). It was shown that the four significantly different values could not be reconciled in terms of experimental error, heterogeneity of intracellular pH, liquid junction potential differences, or binding of indicator molecules inside the fibre. They could, however, be reconciled if the fibre water had different structure and solvent properties from the extracellular water and all ions were distributed across the membrane as between two liquid phases containing different solvents. Then the H+ would be in equilibrium, as shown by the microelectrode measurement, but intracellular pH would be indeterminable and probably greater than 6.

Animals↗
PubMed1986

Two modes of gating during late Na+ channel currents in frog sartorius muscle.

Na+ currents were measured during 0.4-s depolarizing pulses using the cell-attached variation of the patch-clamp technique. Patches on Cs-dialyzed segments of sartorius muscle of Rana pipiens contained an estimated 25-500 Na+ channels. Three distinct types of current were observed after the pulse onset: a large initial surge of inward current that decayed within 10 ms (early currents), a steady "drizzle" of isolated, brief, inward unitary currents (background currents), and occasional "cloudbursts" of tens to hundreds of sequential unitary inward currents (bursts). Average late currents (background plus bursts) were 0.12% of peak early current amplitude at -20 mV. 85% of the late currents were carried by bursting channels. The unit current amplitude was the same for all three types of current, with a conductance of 10.5 pS and a reversal potential of +74 mV. The magnitudes of the three current components were correlated from patch to patch, and all were eliminated by slow inactivation. We conclude that all three components were due to Na+ channel activity. The mean open time of the background currents was approximately 0.25 ms, and the channels averaged 1.2 openings for each event. Neither the open time nor the number of openings of background currents was strongly sensitive to membrane potential. We estimated that background openings occurred at a rate of 0.25 Hz for each channel. Bursts occurred once each 2,000 pulses for each channel (assuming identical channels). The open time during bursts increased with depolarization to 1-2 ms at -20 mV, whereas the closed time decreased to less than 20 ms. The fractional open time during bursts was fitted with m infinity 3 using standard Na+ channel models. We conclude that background currents are caused by a return of normal Na+ channels from inactivation, while bursts are instances where the channel's inactivation gate spontaneously loses its function for prolonged periods.

Action Potentials↗
PubMed1979

Potassium depletion and sodium block of potassium currents under hyperpolarization in frog sartorius muscle.

1. A three-electrode voltage clamp method was used to investigate the mechanism of the fall in resting potassium permeability which occurs under extreme hyperpolarization in frog sartorius muscle fibres. 2. Experiments were performed which show that this permeability change is due to a potential dependent block by Na+ ions present in the external solution. 3. Inward K-currents recorded on hyperpolarization turned off exponentially with time. In the presence of Na the steady-state current-voltage relation had a region of negative slope beyond -140 mV. This negative-slope region was removed when Na was replaced by TMA, Tris or Li. Increasing [Na] to 140 mM shifted the negative-slope region to less negative membrane potentials; reducing [Na] to 14 mM shifted the region to more negative potentials. 4. The time constant for the turn-off of the currents (tau) was the same in Na and TMA-containing solutions at membrane potentials positive to -140 mV. At more negative membrane potentials the tau s in Na became progressively shorter than those in TMA. Increasing [Na] to 140 mM (from 70 mM) gave smaller tau s at all potentials. 5. If fibres were hyperpolarized to -240 mV and then repolarized to -160 mV in 70 mM-Na the current recorded during the second pulse turned on with time, often reaching a value greater than that at the end of the first pulse. This behaviour was removed when Na was replaced by TMA or Tris. 6. An estimate of the steady-state relationship between the degree of block and membrane potential was obtained, and could be fitted by an expression for a potential-dependent ionic block with a very low affinity binding site for Na+ in the membrane. 7. The recovery after hyperpolarization of K-currents at the holding potential was examined in two-pulse experiments. In 70 mM-TMA recovery occurred at the same rate whether the initial hyperpolarization was to -120 or to -210 mV. In 70 mM-Na recovery after an initial pulse to -120 mV occurred at the same rate as in TMA, but recovery after a pulse to -210 mV occurred about 9 times faster. These results are consistent with depletion of K from the lumen of the T-system dominating the turn-off of K currents in TMA and in Na for the hyperpolarization to -120 mV, but a different mechanism being involved for the -120 mV pulse in Na. 8. A three-compartment model is presented which attempts to describe the depletion of K from the T-system. The model accurately predicts the time-course for the decline of inward K-currents, both in 10 and 80 mM-K solutions.

Animals↗
PubMed1979

The relationship between initial creatine phosphate breakdown and recovery oxygen consumption for a single isometric tetanus of the frog sartorius muscle at 20 degrees C.

A previous paper (Mahler, M. 1978 J. Gen. Physiol. 71:559--580) describes the time-course of the suprabasal rate of oxygen consumption (delta QO2) in the sartorius muscle of R. pipiens after isometric tetani of 0.1--1.0 s at 20 degrees C. To test whether these were the responses to impulse changes in the rate of ATP hydrolysis, we compared the total suprabasal oxygen consumption during recovery (delta[O2]) with the amount of ATP hydrolyzed during a contraction, measured indirectly as the decrease in creatine phosphate (delta[CP]O). If suprabasal ATP hydrolysis during recovery is negligible in comparison with that during contraction, delta[CP]0/delta[O2] should approximate the P:O2 ratio for oxidative metabolism, which has an expected value of 6.1--6.5. We found: formula; see text. We conclude that in this muscle at 20 degrees C: (a) after a tetanus of 0.2--1.0 s, delta QO2(t) can be considered the response to an impulse increase in the rate of ATP hydrolysis; (b) the reversal during recovery of unidentified exothermic reactions occurring during the contraction (Woledge, R. C. 1971. Prog. Biophys. Mol. Biol. 22:39--74) can be coupled to an ATP hydrolysis that is at most a small fraction of delta[CP]0; (c) the pooled mean for delta[CP]0/delta[O2], 6.58 +/- 0.55, sets an experimental lower bound for the P:O2 ratio in vivo.

Adenosine Triphosphate↗
PubMed1970

Actions of some cations on the electrical properties and mechanical threshold of frog sartorius muscle fibers.

With the use of a point voltage-clamp technique, the effects of Zn(2+), UO(2) (2+), tetraethylammonium, and several other homologous quaternary ammonium ions on the electrical properties of the frog sartorius muscle and its mechanical threshold were studied. None of the agents separated the voltage thresholds for mechanical activation and delayed rectification. However, Zn(2+), UO(2) (2+), and TEA, which are known to potentiate the twitch, caused some inhibition of the normal increase in potassium conductance during delayed rectification. Zn(2+) and UO(2) (2+) also slowed the rate of development of the outward current. A strength-duration relation was studied for depolarization pulses capable of initiating contraction. With a depolarizing pulse of 2.5 msec the mechanical threshold is about -13 mv at about 20 degrees C. UO(2) (2+), 0.5 microM, which markedly reduced the outward current produced by such a short pulse, did not raise the mechanical threshold. All findings indicate that there is no direct causal relation between delayed rectification and mechanical activation.

Animals↗
PubMed1983

Evidence for an inotropic positive action of cGMP during excitation-contraction coupling in frog sartorius muscle.

Within the realm of the general hypothesis concerning the role of cGMP on intracellular calcium regulation in biological systems, we have investigated the action of cyclic nucleotides during excitation-contraction coupling in frog sartorius muscle. Our data show that several guanosine nucleotides (GTP, GDP, dibutyryl-cGMP) can increase the isometric twitch tension with a maximum increase of 40% in the muscles treated with cGMP. This increase is completely independent of external Ca2+ concentration. The use of dantrolene sodium (known to inhibit calcium release from sarcoplasmic reticulum) results in a decrease in the twitch tension with a contemporary decrease in the intracellular levels of cGMP; whereas, the addition of cGMP to the muscles treated with dantrolene antagonizes, at least partially, the effect of the drug on tension development. Finally, in chemically skinned muscles, cGMP induces a reversible contracture equal to approximately one-half of that evoked by 10(-4) M Ca2+.

Animals↗
PubMed1988

Transposition of the sartorius muscle in the treatment of infected vascular grafts in the groin.

Out of 15 consecutive deep graft-infections during a 5-year-period, 12 cases were treated by local debridement, disinfectants, graft replacement and sartorius muscle transposition. The treatment was successful in 10 cases, which have shown no sign of re-infection. Three grafts occluded during the observation period (2 weeks, 2 months and 15 months), resulting in amputation in one patient. The method is recommended as the treatment of choice in Szilagyi type III infections limited to the groin.

Anti-Bacterial Agents↗