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PubMed1986

Canine experimental free muscle transplantation.

Transplants of the cranial portion of the dog sartorius muscle were able to generate 70% of control force after 3 months if the artery, vein, and nerve were reanastomosed. Our histological and histochemical findings correlate with the functional findings. In a separate group of animals that had their muscles denervated prior to replantation, no collateral sprouting was noted and no function could be recorded when the nerve was stimulated proximally. These findings suggest that clinical application of free muscle transplantation is strongly supported by this animal model if due consideration is paid to surgical procedure and anatomical structure.

Animals↗

PubMed1984

Direct measurement of intracellular free magnesium in frog skeletal muscle using magnesium-selective microelectrodes.

Mg2+-selective microelectrodes have been used to measure the intracellular free Mg2+ concentration in frog skeletal muscle fibers. Glass capillaries with a tip diameter of less than 0.4 micron were backfilled with the Mg2+ sensor, ETH 1117. In the absence of interfering ions, they gave Nernstian responses between 1 and 10 mM free Mg2+. In the presence of an ionic environment resembling the myoplasm, the microelectrode response was sub Nernstian (18-24 mV) but still useful. The electrodes were calibrated before and after muscle-fiber impalements . In quiescent fibers from sartorius muscle (Rana pipiens), with resting membrane potentials not less than -82 mV, the intracellular free Mg2+ concentration was 3.8 +/- 0.41 (S.E.) mM (n = 58) at 22 degrees C. No significant change in the intracellular free Mg2+ was observed following extensive (approx. 6 h) incubation in Mg2+-free media. Increasing the external concentration of magnesium from 4 to 20 mM (approx. 15 min) produced a slow and small enhancement (1.8 mM) of [Mg2+]i, which was fully reverted when the divalent cation was removed from the bathing solution. No change in ionic magnesium resting concentration was observed when the muscle fibers were treated either with caffeine 3 mM or with Na+-free solutions. In depolarized muscle fibers (-23 +/- 2.7 mV) treated with 100 mM K+, the myoplasmic [Mg2+] was 3.7 +/- 0.45 (S.E.) mM, n = 6, immediately after the spontaneous relaxation of the contracture. Similar determinations in muscle fibers during stimulation at low frequency (5 Hz), and after fatigue development, showed no changes in the concentration of free cytosolic Mg2+. These results point out that [Mg2+]i is not modified under these three different experimental conditions.

Animals↗

PubMed1983

Potassium propionate causes preferential loss of 'bound' acetylcholine in frog muscle.

Bound and free acetylcholine (ACh) were measured in frog sartorius muscles by mass fragmentography. Upon incubation of the muscles for 5 min with potassium propionate, which stimulated the release of ACh, there was a 2-fold reduction of bound ACh. In contrast, the amount of free ACh remained unchanged. After 65 min recovery from stimulation in normal Ringer solution containing deuterium-labelled choline, free ACh was labelled to a higher degree than bound ACh. The results are in agreement with the idea that ACh is synthesized in the cytoplasmic compartment of the motor nerve terminal, and subsequently transferred to the vesicles from which it is released upon stimulation.

Acetylcholine↗

PubMed1997

Osmotic 'detubulation' in frog muscle arises from a reversible vacuolation process.

Isolated Rana temporaria sartorius muscle fibres were subject to introduction and subsequent withdrawal of 400 mM extracellular glycerol, exposures to high divalent ion concentrations and then cooling. Tubular detachment was then assessed through changes in the action potential afterdepolarization. (1) The rapid (5-10 min) rather than slow cooling step (30 min) produced a gradual (30 min) development of detubulation arrested by the subsequent replacement of glycerol and reversed by addition of 350 mM sucrose. Such osmotic agents influenced neither resting potentials of intact or detubulated fibres nor action potentials in intact fibres. (2) Full tubular detachment was achieved by 40 min. Laser epifluorescence microscopy demonstrated an accompanying tubular vacuolation through its trapping of a Rhodamine dye. (3) Subsequent re-additions (at 10-80 min) of glycerol restored the afterdepolarization in 30% of detubulated fibres and correspondingly reduced vacuolation. Sustained (> 60 min) exposures to 350 mM sucrose, applied between 30-60 min, both reversed tubular isolation in 70% of detubulated fibres and abolished tubular vacuolation. Finally, results from transient (10-30 min) sucrose exposures resembled the consequences of sustained applications of glycerol, suggesting that detubulation and its reversal result from an osmotic mechanism. (4) Nevertheless, irreversible changes developed after 70-80 min in 70% of detubulated fibres, a process hastened by slow cooling steps in the initial osmotic stress. The present study thus correlates morphological and electrophysiological consequences of applying osmotic shock to skeletal muscle for the first time. It additionally differentiates reversible and irreversible components of detubulation. Finally, it suggests that detubulation results from the similarly reversible vacuolation observed under comparable osmotic conditions, and that such vacuolation can eventually lead to irreversible detubulation.

Action Potentials↗

PubMed1961

The fine structure of neuromuscular junctions and the sarcoplasmic reticulum of extrinsic eye muscles of Fundulus heteroclitus.

The extrinsic eye muscles of the killifish (F. heteroclitus) were fixed in OSO(4) (pH 7.6) and subsequently dehydrated, embedded, and sectioned for electron microscopy. The fine structures of neuromuscular junctions and of sarcoplasmic reticulum were then observed. The neuromuscular junction consists of the apposition of axolemma (60 to 70 A) and sarcolemma (90 to 100 A), with an intervening cleft space of 200 to 300 A, forming a synaptolemma 400 to 500 A thick. The terminal axons contain synaptic vesicles, mitochondria, and agranular reticulum. The subsynaptic sarcolemma lacks the infolding arrangement characteristic of neuromuscular junctions from other vertebrate skeletal muscle, making them more nearly like that of insect neuromuscular junctions. A comparison between the folded and non-folded subsynaptic membrane types is made and discussed in terms of comparative rates of acetylcholine diffusion from the synaptic cleft and resistances of the clefts and subsynaptic membranes. The sarcoplasmic reticulum consists of segmentally arranged, membrane-limited vesicles and tubular and cisternal elements which surround individual myofibrils in a sleeve-like arrangement. Triadic differentiation occurs at or near the A-I junction. Unit sleeves span the A and I bands alternately and consist of closed terminal cisternae interconnected across the A and I bands by tubular cisternae. The thickness of the sarcoplasmic membranes increases from 30 to 40 A in intertriadic regions to 50 to 70 A at the triads. The location of the triads is compared with previously described striated muscle from Ambystoma larval myotomes, cardiac and sartorius muscles of the albino rat, mouse limb muscle, chameleon lizard muscle, and insect muscle, with reference to their possible role in intracellular impulse conduction.

Animals↗

PubMed1959

The distribution and kinetics of release of radiocalcium in tendon and skeletal muscle.

The distribution of Ca(45) in frog (Rana pipiens) sartorius muscle, after 4 hours' exposure to Ringer's solution containing radiocalcium, has been analyzed by observing the kinetics of escape of the radioisotope into a non-radioactive Ringer's solution with calcium present or absent and by assuming that the tendon of Achilles is a satisfactory model of the extent of the uptake and release of Ca(45) by the interstitial connective tissue (c.t.). In a Ringer's solution containing 1 mM/liter calcium, the exchangeable calcium distribution in micromoles per gram wet weight is as follows: (a) Aqueous phase of c.t. space: 0.16; (b) bound to c.t.: 0.16; (c) bound to surface of fibers: 0.13, of which 0.03 is displaced only by self-exchange, whereas the rest, as in c.t., can be displaced by other ions; and (d) in myoplasm: 0.33. The kinetics of Ca(45) exit suggests that in infinite time of exposure to Ca(45) the myoplasmic component would rise to 0.85. In the muscles, the half-time of the quickly emerging Ca(45) averages about 3 minutes, whereas the time constant of the slowly released component is about 500 minutes. In the tendons the percentage rate of escape falls exponentially, the half-time of emergence being about 10 minutes.

Animals↗

PubMed1961

In vitro studies of the gain and exchange of calcium in frog skeletal muscle.

(1) The Ca(++), Na(+), and K(+) contents of frog sartorius muscles were found analytically after exposure to various media including some containing labeled Ca(++). (2) During storage in media with 100 to 120 mM Na(+) and 1 mM Ca(++) both Na(+) and Ca(++) are gained while K(+) is lost; there is a high correlation between Na(+) and Ca(++) gains. (3) When Ca(++) gain occurs from a solution containing labeled Ca(++) there is also some exchange of the original Ca(++) with the labeled Ca(++). The amount exchanged is considerably less (e.g. 50 per cent) than the total amount of labeled Ca(++) taken up by the tissue. (4) When the external Na(+) concentration is reduced to 30 mM the amount of labeled Ca(++) taken up is increased. Part of the increase is attributable to a greater net gain and part to a greater degree of exchange. (5) It is pointed out that muscles which have been loaded in vitro with labeled Ca(++) will not provide a valid measure of the exchangeability of the normal Ca(++) content present at the time of dissection. (6) Comparison is made between results obtained using Sr(89) and Ca(45) as labels for the Ca(++). Little, if any, difference is perceptible.

Animals↗

PubMed1963

Effects of zinc on responses of skeletal muscle.

Zn(++) potentiates the twitch tension of the frog's sartorius muscle by as much as two to three times, and prolongs twitch time parameters. Tetanus tension is unchanged, but fusion frequency is reduced. Thus, the basic mechanical effect of Zn(++) is prolongation, but not intensification, of the active state. Threshold effects appear at about 0.005 mM Zn(++), and maximal changes at 0.05 mM. In 0.05 mM, potentiation begins after a delay of about 1 min. and develops with half-time of 6 min.; full changes reverse in pure Ringer's with halftime of 60 min. Diffusion theory analysis of these kinetics indicates that the potentiating action of zinc involves special features not found in potentiation by anions: a primary membrane action is not excluded, but Zn(++) may have to penetrate to and act at sarcoplasmic reticular or myoplasmic sites. Zn(++) does induce excitatory membrane effects: the fall of the action potential is slowed and the refractory period is increased about four times; but excitability as such is not changed. Unique chemical features of Zn(++) are discussed in relation to possible mechanisms of its action on muscle fibers.

Action Potentials↗

PubMed1967

The extracellular space of voluntary muscle tissues.

The volume occupied by the extracellular space has been investigated in six types of voluntary muscles: sartorius (frog), semitendinosus (frog), tibialis anticus longus (frog), iliofibularis (frog), rectus abdominis (frog), and diaphragm (rat). With the aid of four types of probe material, three of which are conventionally employed (inulin, sorbitol, sucrose) and one of which is newly introduced (poly-L-glutamate), and a different experimental method, we have demonstrated that the "true" extracellular space of frog sartorius, semitendinosus, tibialis anticus longus, and iliofibularis muscle and of rat diaphragm muscle is equal to, or probably less than, 8-9% (v/w) of the tissue. The frog rectus muscle shows a somewhat higher ceiling value of 14%.

Animals↗

PubMed1972

Electrical properties and excitation-contraction coupling in skeletal muscle treated with ethylene glycol.

The contractility of the frog sartorius muscle was suppressed after treatment with a Ringer solution added with ethylene glycol (EGR). No contraction was elicited by nerve stimulation when the muscle was brought back to normal Ringer solution after having been soaked in 876 mM EGR for 4 hr or in 1095 mM EGR for 2 hr. However, the action potential of normal amplitude was generated and followed by a depolarizing afterpotential. The resting membrane potential was slightly decreased from the mean normal value of -91.1 mv to -78.8 mv when 1095 mM EGR was used, and to -82.3 mv when 876 mM EGR was used, but remained almost constant for as long as 2 hr. The afterpotential that follows a train of impulses and a slow change in membrane potential produced by a step hyperpolarizing current (so-called "creep") were suppressed after treatment with ethylene glycol. The specific membrane capacity decreased to about 50% of the control values while the specific membrane resistance increased to about twice the control values Therefore, the membrane time constant remained essentially unchanged. The water content of the muscle decreased by about 30% during a 2 hr immersion in 1095 mM EGR, and increased by about 30% beyond the original control level after bringing the muscle back to normal Ringer. The intracellular potassium content did not change significantly during these procedures. Some differences between the present results and those obtained with glycerol are discussed.

Action Potentials↗

PubMed1975

Longitudinal impedance of single frog muscle fibers.

The longitudinal impedance of single skeletal muscle fibers has been measured from1 to 10,000 Hz in an oil gap apparatus which forces current to flow longitudinally down the fiber. The impedance observed is purely resistive in some fibers from the semitendinosus muscle and in two fibers from the sartorius muscle. In other fibers from the semitendinosus muscle a small phase shift is observed. The mean value of the maximum phase shift observed from all fibers is 1.07 degrees. The artifacts associated with the apparatus and method are examined theoretically and it is shown that one of the likely artifacts could account for the small phase observed. It is concluded that the longitudinal impedance of skeletal muscle fibers is essentially resistive and that little, if any, longitudinal current crosses the membranes of the sarcoplasmic reticulum.

Animals↗

PubMed1971

A comparison of the spindles in two different muscles of the frog.

1. The responses of spindles in the iliofibularis muscle of frogs to stretch during either small motor nerve fibre stimulation or the application of suxamethonium were compared.2. All spindles which were excited by small motor nerve fibre stimulation were also excited by suxamethonium, and their responses to these two methods of excitation were very similar. The drug dose was usually 5-10 mug/ml. but smaller and larger doses were effective. Large doses (> 100 mug/ml.) could sometimes lead to a reversible partial block of the spindle response to stretch.3. Suxamethonium also caused a prolonged contraction in extrafusal slow muscle fibres. This contraction was not responsible for the effect on the spindle, because the time course of its action on the muscle tension and on the spindle afferent was different.4. It was concluded that suxamethonium stimulated prolonged contraction in the small intrafusal muscle fibres, which are known to be innervated by the small motor nerve fibres.5. Only about half of the spindles in the iliofibularis muscle were excited by suxamethonium.6. In the sartorius muscle which has no slow extrafusal muscle fibres, no spindles were found to be excited by suxamethonium in the way characteristic of that due to small intrafusal muscle fibre contraction.7. It is concluded that, in frog muscles which have no slow extrafusal fibres, the muscle spindles do not have small intrafusal muscle fibres of the kind found in the iliofibularis muscle.

Animals↗

PubMed1978

Association of increased pHi with calcium ion release in skeletal muscle.

The pH difference across the cell membrane of frog sartorius muscle cells was measured with the distribution of 5,5-dimethyl-2,4-oxazolidine-dione (DMO) as the marker. Depolarization of the muscles to values at or below the contraction threshold caused by elevating external potassium up to approximately 20 mM resulted in an internal alkalinization. The change was smaller with superthreshold depolarization (20--30 mM [K+]). The alkalinization was blocked by agents that block calcium release from the sarcoplasmic reticulum (procaine and dantrolene sodium). Other agents that cause calcium release (caffeine, theophylline, and quinine) were found to give alkalinization when tested at concentrations just below the contracture threshold. Increased acidification of the extracellular medium was associated with the internal alkalinization. The data were interpreted as indicating the presence of a calcium-stimulated H+ and/or OH- ion transport system in the muscle membrane.

Animals↗

PubMed1984

Blocking effects of a new component, paeoniflorigenone, in paeony root on neuromuscular junctions of frogs and mice.

A new monoterpene, paeoniflorigenone (PFG) (100-900 micrograms/ml), which was isolated from paeony roots and identified chemically, suppressed both indirectly and directly stimulated muscle twitchings of frog sciatic nerve-sartorius muscle preparation, and it indirectly stimulated muscle twitchings of phrenic nerve-diaphragm muscle preparations. The suppression effect by PFG (300 micrograms/ml) on twitching was not reversed by neostigmine (60 micrograms/ml) and was restored by washing out of PFG. PFG (150 micrograms/ml) depolarized the diaphragm muscle membranes by 10 mV and did not change the electrotonic potentials. PFG (100 micrograms/ml) inhibited weakly acetylcholine (5 micrograms/ml)-induced slow contractions. These results demonstrated that PFG is a depolarizing neuromuscular blocking agent, being similar to succinylcholine, except that PFG did not produce any contraction, but succinylcholine did.

Acetylcholine↗

PubMed1984

Thermoelastic effect in chemically skinned frog skeletal muscle in rigor.

The thermoelasticity in rigor muscle was investigated using chemically skinned frog sartorius muscles. The use of chemically skinned muscles enabled us to study the thermoelasticity under various intracellular circumstances. Effects on the thermoelasticity of the presence or the absence of Ca and the lowering of pH in the rigor solution were investigated. All values of the thermoelastic heat: tension ratios obtained under various circumstances were within the range reported for active muscles. In rigor state, the cross-bridges are fixed on the thin filaments and head can no longer rotate. Hence the present results indicate that the thermoelasticity in active muscles originates from the thermoelasticity of the myofilaments or the cross-bridges.

Animals↗

PubMed1989

Intrafusal muscle fibre types in frog spindles.

Muscle spindles from bullfrog semitendinosus, iliofibularis and sartorius muscles were examined with light and electron microscopy. Four types of intrafusal muscle fibre were identified according to their diameter, central nucleation and reticular zone arrangement: a large nuclear bag fibre, a medium nuclear bag fibre, and two types of small nuclear chain fibres with and without a reticular zone, respectively. It is suggested that they are comparable to the nuclear bag1, bag2 and chain fibres in mammalian muscle spindles.

Animals↗

PubMed1978

The properties of the extraocular muscles of the frog. III. Morphological, mechanical and pharmacological properties of the isolated retractor bulbi muscle.

Some morphological, physiological, and pharmacological properties of the retractor bulbi muscle of the frog were tested. The enzyme-histochemical investigation shows that the retractor bulbi muscle contains twitch muscle fibres only. Two types of twitch muscle fibres, which are especially different in their diameter and in the content of mitochondria, build the muscle in an irregular arrangement; tonic muscle fibres were not observed. On the average, the isolated retractor bulbi muscle has at room temperature a contraction time of 26 ms, a half-relaxation time of 28 ms, a fusion frequency of 75 stimuli/s, and a twitch-tetanus ratio of 0.28. The fatigability of this muscle is higher than in oculorotatory eye muscles but lower than in skeletal muscles of the frog. An increase of the extracellular K+-concentration elicits in retractor bulbi muscles a quickly transient contracture; the mechanical threshold of the muscle fibres is found in a range between 20 and 25 mM K+ in Ringer solution. Similar short-lasting contractures, which are probably caused by twitch fibres, rich in mitochondria, are also evoked by application of depolarizing drugs like acetylcholine. The properties of the retractor bulbi muscle are compared with those of the sartorius muscle of the frog, which likewise contains twitch muscle fibres only.

Acetylcholine↗

PubMed1980

Bound potassium in muscle II.

Experiments were performed to decide between the alternatives a) the ionized K+ is in a dissolved state in the muscle water, or b) a part of the muscle potassium is in a "bound' state. Sartorius muscles of Rana esculenta were put into glicerol for about one hour at 0-2 degrees C. Most of muscle water came out, but most of muscle potassium remained in the muscles. In contrast to this: from muscle in heat rigor more potassium was released due to glicerol treating than from the intact ones. 1. Supposition a) is experimentally refuted. 2. Supposition b) corresponds to the experimental results.

Animals↗