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PubMed1967

The pH sensitivity of the chloride conductance of frog skeletal muscle.

1. The effect of changes in the pH of the extracellular solution on the membrane conductance of frog sartorius and toe muscle fibres was measured with intracellular micro-electrodes.2. In Ringer solution the membrane conductance was found to be highly sensitive to changes in pH between 5.0 and 9.8. In alkaline solution the conductance rose; in acid solution it fell.3. After replacement of chloride by the relatively impermeant methylsulphate ion the membrane conductance showed little change when pH was altered. It is concluded that chloride is the ion species principally concerned in the pH sensitivity of the resting membrane conductance.4. The relation between pH and the chloride conductance was sigmoid, with the steepest part of the curve lying in the region of neutrality.5. The membrane conductance of muscles equilibrated in a 100 mM-K 216 mM-Cl solution was also sensitive to changes of extracellular pH. As in Ringer solution, the membrane conductance rose in alkaline and fell in acid solutions in a sigmoid fashion.6. Sartorius muscles in isotonic potassium methylsulphate solution showed no change in membrane conductance at different pH values.7. In chloride-free solution a fall in pH tended to cause depolarization; a rise in pH had the opposite effect.8. In Ringer solution the initial effect of a rise in pH was usually a transient depolarization. The indication is that the intracellular concentration of chloride ions may be slightly in excess of that which corresponds to the resting potential. The long-term effects of changes in pH on the membrane potential in Ringer solution were in the same direction as in the absence of chloride.9. The transient potential changes produced on addition and withdrawal of chloride ions were found to be larger in alkaline solutions than in acid solutions. This is further evidence for a higher chloride permeability in alkaline solutions.

Animals↗

PubMed2003

Response of broilers selected on carcass quality to dietary protein supply: live performance, muscle development, and circulating insulin-like growth factors (IGF-I and -II).

The effect of dietary protein supply on muscle development and circulating concentrations of insulin-like growth factors (IGF)-I and -II was examined in chickens selected for increased breast yield and decreased fatness (quality, QL) and in its control line (CL). CL and QL chickens were fed isoenergetic diets containing 121.5 or 215.8 g CP/kg during a 12-d period; comparisons were performed at 33 d of age. Birds given the high protein diet grew faster, ate less feed, had lower feed conversion ratio (FCR), and higher muscle weights than their counterparts given the low protein diet. The muscle weight response to protein supply differed between muscles in both lines, with pectoralis major appearing more sensitive than sartorius. The response of the gastrocnemius muscle depended on the line. Selection for carcass quality increased (P < 0.01) body weight, growth rate, feed intake, pectoralis major and sartorius muscle weights, and pectoralis major muscle proportion. There was, however, no line difference in FCR or in sartorius muscle proportion. The weight and proportion of the gastrocnemius muscle were higher (P < 0.05) in the QL than the CL chickens on the high protein diet, but there was no line difference for the low protein diet. Plasma levels of IGF-I, and to a lesser extent IGF-II, were lower (P < 0.01) in protein-restricted chickens. No difference in circulating IGF-II was observed between the lines. Concentrations of IGF-I were higher (P < 0.05) in QL than CL chickens, which may contribute to improved body composition for this genotype.

Animal Feed↗

PubMed1986

Differences in transmitter release and number of nerve terminals per motoneuron between two frog muscles.

Recent studies suggest that the number of nerve terminals maintained per motoneuron and perhaps other motoneuron properties (Grinnell and Herrera, 1980a; Grinnell and Trussell, 1983) influence transmitter release. We have examined, in detail, the structure and function of motoneurons innervating two different twitch muscles, the sartorius and the ext. long. dig. IV (e.l.d.) in the adult frog using histochemical and electrophysiological techniques. These studies were undertaken with a view towards learning whether differences in the number of nerve terminals per motoneuron were correlated with differences in transmitter release between motoneurons innervating these two muscles. Moreover, these studies provide detailed, quantitative data that are a necessary prerequisite for carrying out additional studies to examine the possible influence of muscle on transmitter release properties. In low Ca2+-high Mg2+ Ringer's solution, mean quantal content (m) and miniature end-plate potential (MEPP) frequency were larger at sartorius than at e.l.d. end-plates. The mean length of nerve terminals was also found to be greater in sartorius than in e.l.d. muscles. When release was normalized for the difference in terminal length, m remained larger in the sartorius, whereas MEPP frequency in the two muscles was similar. Cell bodies of individual sartorius motoneurons were greater in cross-sectional area and maintained approximately 5.6-fold greater aggregate length of nerve terminals per motoneuron than did e.l.d. motoneurons. This greater aggregate length of nerve terminal contact with their respective target muscles is primarily a result of a greater number of nerve terminals supported by sartorius than by e.l.d. motoneurons.(ABSTRACT TRUNCATED AT 250 WORDS)

Action Potentials↗

PubMed1989

Primary afferent depolarization of central terminals of group II muscle afferents in the cat spinal cord.

1. The origin of primary afferent depolarization (PAD) of the central terminals of group II afferent fibres of tibialis anterior and extensor digitorum longus muscles has been investigated in the cat. Changes in the excitability of the terminals to intraspinal stimuli, upon application of conditioning stimuli to muscle nerves (quadriceps, sartorius, gracilis, posterior biceps-semitendinosus, anterior biceps-semimembranosus, gastrocnemius-soleus, deep peroneal), cutaneous nerves (sural, superficial peroneal) and the posterior nerve to the knee joint, were used as a measure of PAD. 2. PAD was most readily evoked by conditioning stimuli which were maximal for group II muscle afferents. However, some PAD was also evoked from group I afferents and evidence is presented that group Ia afferents contributed. Afferents of posterior biceps-semitendinosus and sartorius muscles appeared to be most effective. PAD was also evoked by stimulation of cutaneous and joint nerves, often in the same fibres which were affected by group Ia afferents. 3. It is concluded that there are several common sources of PAD of group II and group Ia afferent terminals on the one hand, and group Ib afferent terminals on the other. 4. The properties of PAD of group II afferents are discussed in relation to the problem of how PAD affects transmission from fibres with long terminal branches of small diameter.

Action Potentials↗

PubMed1981

Postsynaptic inhibition of neuromuscular transmission by trifluoperazine.

The effect of trifluoperazine (TFP) on neuromuscular transmission was investigated on chick biventer cervicis and frog cutaneous pectoris and sartorius nerve-muscles. In the chick, TFP inhibited indirectly elicited twitches in a frequency-dependent manner. Inhibition was much more rapid at higher frequencies of stimulation. Directly elicited twitches, KCl contracture and action potentials of desheathed frog sciatic nerve and sartorius muscles were unaffected by TFP, suggesting an action of TFP on neuromuscular transmission. TFP depressed end plate potential amplitude and miniature end plate potential (MEPP) amplitude without affecting MEPP frequency. When MEPP frequency was increased by high Na+ Ringer, depression of MEPP amplitude was much more rapid. Similarly, at high frequencies of stimulation (100 Hz), TFP rapidly depressed end plate currents. TFP inhibited contractures induced by bath-applied acetylcholine (ACh); depressed ACh potentials produced by iontophoretically applied ACh; decreased ionic current and time constant of decay of end-plate currents of transected muscle; and inhibited [alpha-125I]bungarotoxin binding to ACh receptor. These data suggest that TFP acts postsynaptically in a frequency-dependent manner to inhibit neuromuscular transmission. Based on recent evidence that TFP is a potent antagonist of calmodulin and that calmodulin is localized mainly to postsynaptic regions, we postulate that the postsynaptic inhibitory actions of TFP may be mediated through antagonism of calmodulin, which in turn may regulate ACh receptor function.

Acetylcholine↗

PubMed1979

Properties of motor units of the frog iliofibularis muscle.

The tension developed by single motor units of the iliofibularis muscle of the frog Litoria aurea was recorded in response to single-shock and repetitive stimulation of motor axons. The majority of units in each muscle, 13 on the average, were of the twitch type; an additional 4 units were slow or tonic. It appeared that slow units comprised a single homogeneous population, but two types of twitch units could be recognized: small fatigue-resistant units with long twitch times to peak (20--40 ms) and larger, fatigable units with briefer times to peak (16--27 ms). Evidence from a comparison of unit tetanic tensions indicated the presence of polyneuronal innervation of both slow and twitch muscle fibers. The relatively low incidence of polyneuronal innervation of twitch fibers in iliofibularis, when compared with a muscle like sartorius (9), was attributed to the difference in lengths of muscle fibers in the two muscles. It was argued that slow muscle fibers probably receive a multiterminal as well as polyneuronal innervation, with the terminals of any one axon lying widely spaced along the muscle fiber.

Animals↗

PubMed1987

Relationship between mitochondrial volume density and capillarity in hamster muscles.

Mitochondrial volume density and lipid droplet-volume density were stereologically determined from electron micrographs of muscle fibers from three hamster muscles: retractor, sartorius, and soleus. The number of capillaries around a fiber, length of capillary-fiber contact, and muscle fiber area were also measured. Glycolytic fibers of the retractor and sartorius had larger cross-sectional areas, lower mitochondrial-volume densities, fewer subsarcolemmal aggregates of mitochondria, and lower capillary-fiber contact length in comparison to oxidative fibers of the retractor and soleus. Values for mitochondrial volume density in the different muscles correlated well (r = 0.97) with resting O2 consumption. The mitochondrial volume densities for each muscle correlated well (r = 0.99) with O2 diffusion coefficients of these muscles. Our results indicate that an analysis of the adequacy of O2 supply to an individual muscle fiber must take into account an interplay among fiber size, percent of the muscle fiber perimeter in contact with a capillary (capillary-fiber contact), and O2 demand of the fiber estimated by mitochondrial volume density.

Animals↗

PubMed1981

Three-dimensional observation on muscular tissues.

Striated muscle cells of frog sartorius and smooth muscle cells of guinea pig taenia coli were observed three-dimensionally by field emission type scanning electron microscope (FE-SEM) and freeze-fracture deep-etching replica (FFDE) method. By tearing at different preparative stages, various cellular structures appeared on SEM: the outer surface of cells, the inner surface of plasmalemma, and the interior of cells. On the inner surface of the plasmalemma of striated muscle, many caveolae, membranous structures and fine filaments were observed. Inside the cells myofibrils showed the characteristic banding pattern and on the thick filaments, a periodicity of 40 nm was observed. Along the myofibril, T-tubules and sarcoplasmic reticulum were seen with their regional differentiations. In smooth muscle cells, on the inner surface of the plasmalemma there were many caveolae, bundles of filaments and endoplasmic reticulum. The central part of smooth muscle cells were occupied by their nucleus, many microtubules, mitochondria and rough surfaced endoplasmic reticulum. By the FFDE method, observations on finer details were added to the SEM studies, including lateral projections of myosin filaments in striated muscles and fine filaments connecting thin myofilaments in smooth muscle cells. In the terminal cistern of the sarcoplasmic reticulum, networks composed of granular materials were observed.

Animals↗

PubMed1982

Effect of chloride withdrawal on the geometry of the T-tubules in amphibian and mammalian muscle.

The relative chloride permeabilities of the T-tubule membranes in mammalian (rat sternomastoid) and amphibian (toad sartorius) skeletal muscle fibers have been assessed from the change in volume of the T-tubules during chloride withdrawal from fibers exposed to low extracellular chloride concentrations. A 3.5- to 4.2-fold increase in T-tubule volume was found in mammalian fibers, and this was shown to be independent of the composition of the low chloride solution or the nature of the fixative used in preparation for electron microscopy. The increase in T-tubule volume was transient and was inhibited by factors which block chloride conductance, i.e., low pH, 2,4-dichlorophenoxyacetic acid, and nitrate ions. A small increase (1.48-fold) in T-tubule volume was seen in amphibian fibers when chloride ions were replaced by sulphate ions. No increase in volume was observed in amphibian T-tubules when methyl sulphate ions replaced chloride ions. The results support the idea that the chloride permeability of the T-tubule membrane is significantly higher in mammalian fibers than in amphibian fibers.

2,4-Dichlorophenoxyacetic Acid↗

PubMed1982

Decrease in stiffness during shortening in calcium activated skinned muscle fibers.

Single fibers from frog sartorius or semitendinosus muscle were mechanically skinned and activated in ATP salt solution containing 10 micro M Ca2+ (7 degrees C). After development of an isometric contraction, fibers were released at constant speed (0.03-2.4 s-1). During ramp shortening, stiffness was determined from the slope of the tension-length diagram obtained during superimposed quick stretches. Both force and stiffness decreased, as the ramp shortening proceeded and approached a steady value after about 60 ms. An increase in speed of shortening caused a decrease in fiber tension and stiffness and an increase in the ratio of stiffness to tension, suggesting a decrease in both the number of attached crossbridges and in the average force per crossbridge.

Animals↗

PubMed1987

Properties enhancing aerobic capacity of calling muscles in gray tree frogs Hyla versicolor.

The muscle features that accommodate the extraordinarily high aerobic respiration during calling by the gray tree frog Hyla versicolor were examined. We compared the muscles used for calling by males (external and internal obliques and laryngeal muscles) with the homologous muscles of females and with the leg muscles of males and females. The leg muscles consisted of 75% by volume fast glycolytic fibers, a composition typical of other muscles described in anuran amphibians. In contrast the calling muscles of males consisted of 100% fast oxidative fibers and had citrate synthase (CS) activities among the highest recorded for ectothermic vertebrates, 65-80 mumol X min-1 X g fresh mass-1. We also noted a strong sexual dimorphism in size and oxidative capacity of these muscles. The external and internal obliques of females weighed an order of magnitude less than the corresponding muscles of males and had CS activities of only 6 mumol X min-1 X g-1. Morphometric measurements of transmission electron micrographs revealed that the calling muscles of males contained high mitochondrial densities (approximately 20% of fiber volume) and capillary densities (approximately 700 mm-2) compared with a representative hindlimb muscle, the sartorius (mitochondrial density, 6% of fiber volume; capillary density, 230 mm-2). These frog muscles, which operate at approximately 20 degrees C, have lower capillary densities per mitochondrial volume than are found in mammalian muscles that function at higher temperatures.

3-Hydroxyacyl CoA Dehydrogenases↗

PubMed2006

Determination of thigh muscle stiffness using magnetic resonance elastography.

PURPOSE: To measure the elastic properties of the vastus lateralis (VL), vastus medialis (VM), and sartorius (Sr) muscles using magnetic resonance elastography (MRE). MATERIALS AND METHODS: To obtain a normative database of the aforementioned muscles, oblique scan directions were prescribed passing through each muscle. Shear waves were induced into the muscles using pneumatic and mechanical drivers at 90 and 120 Hz, respectively. These drivers were attached to the distal end of the right thigh with the knee flexed at 30 degrees . The foot was placed in a footplate containing MR-compatible load cells to record the force during a contraction (10% and 20% of the maximum voluntary contraction). RESULTS: The shear moduli measured at rest in the VL (N = 12), VM (N = 14), and Sr (N = 13) were 3.73 +/- 0.85 kPa, 3.91 +/- 1.15 kPa, and 7.53 +/- 1.63 kPa, respectively. The stiffness of both vasti increased with the level of contraction, while the stiffness of the Sr remained the same. CONCLUSION: The MRE technique was able to approximate the stiffness of different thigh muscles. Furthermore, the wave length was sensitive to the morphology (unipennate or longitudinal) and fiber composition (type I or II) in each muscle.

Adult↗

PubMed1988

[Nonuniformity of the fine structure of various portions of the nerve terminal in frog somatic muscles as the basis for the variation in its efficiency].

The ultrastructure of serially sectioned single terminals of two neuromuscular synapses differing in efficacy in frog sartorius and cutaneous pectoris muscles was investigated. Their central (CP) and distal (DP) parts were studied morphometrically, and the data on the terminal ultrastructure in different muscles were compared. The areas of active zones (AZ) in CP of terminals in both the muscles were significantly larger than in DP. At the same time the number of AZ in CP specific terminal length of sartorius muscle exceeded that in DP, whereas at terminal of cutaneous pectoris muscle the AZ were arranged more uniformly along the whole terminal length. Some other structural features of these terminals were revealed exerting their influence on the efficacy of transmitter release. We suggest that changes of AZ dimensions may closely correspond to the efficacy both in different parts of the same terminal and in two different terminals.

Animals↗

PubMed2003

Muscle development, insulin-like growth factor-I and myostatin mRNA levels in chickens selected for increased breast muscle yield.

Insulin-like growth factor-I (IGF-I) and myostatin (MSTN) are paracrine regulators of muscle growth. The present study was conducted to relate their expression with muscle fibre development in chickens selected for high breast meat yield and their controls. Both mRNA levels were measured by real-time RT-PCR in the Pectoralis major (PM) muscle between 14 days in ovo and 6 weeks post-hatch and in the Sartorius (SART) muscle between 2 and 6 weeks. The data show that PM growth was slow during in ovo development and rapid in the early post-hatch period. Chickens from the selected genotype exhibited significantly higher breast muscle yields from 2 to 6 weeks of age, and muscle fibre hypertrophy. In the PM, IGF-I and MSTN mRNA levels decreased markedly around hatch, while the IGF-I/MSTN ratio increased, suggesting that it could contribute to the explosive growth observed in the early post-hatch period. Between 4 and 6 weeks of age in selected chickens, IGF-I mRNA levels were significantly higher (p=0.04) with a similar trend in MSTN mRNA levels (p=0.07) in the PM muscle but not in the SART muscle. Our results support the hypothesis that the relative levels of IGF-I and MSTN mRNA may participate to set muscle growth rate along development, while other factors are required to explain differences between genotypes.

Animals↗

PubMed1995

[The characteristics of the impulse activity of the motor units of the muscles in the pelvic floor in the cat].

The investigation have been designed to elucidate the background and thermoregulatory activity (TA) of the motor units (MUs) of pelvic floor muscles (m. spincter ani externus, m. levator ani) and hind limb muscle (m. sartorius) in cats under anesthesia. The MUs of m. sphincter ani externus presented two patterns of background activity--the stationary and the rythmical ones. M. levator ani and m. sartorius presented no activity at room conditions (+22 degrees C). General cooling evoked TA in all the investigated muscles. The discharge frequencies of pelvic floor MUs (4-8 imp/s) during TA were shown to overlap with those of hind limb, muscles (5-9 imp/s). The correlation of MUs bioelectrical characteristics with histochemical and contractile properties of m. sphincter ani externus as fast-twitch muscle is discussed. The possible mechanisms responseble for MUs control in skeletal muscles with different specialization in modulated thermoreceptory afferent input are proposed.

Animals↗

PubMed1996

Age-related changes of protein turnover in specific tissues of the chick.

The effect of age on muscle and liver protein turnover was analyzed in growing broilers. Protein turnover was compared in the Pectoralis major (PM), the Anterior Latissimus dorsi (ALD), and the Sartorius (SART) muscles, as well as in the liver in broilers at three ages (2, 3, and 4 wk). Protein fractional synthesis rates (FSR, in percentage per day) were measured by a flooding dose of L-[4-3H] Phe. Protein fractional breakdown rates (FBR, in percentage per day) were estimated as the difference between FSR and the gain rates of tissue protein. When expressed in absolute rates (grams per day), tissue protein deposition increased during chick growth (approximately 1.7-fold, whatever the tissue). This phenomenon was accompanied by increased protein synthesis (ASR) and proteolysis (ABR) in the PM and in the ALD muscles as well as in the liver. However, ASR and ABR did not seem to be significantly modified in SART. The FSR in skeletal muscles significantly decreased with age. This developmental decline was associated with decreases in RNA content and RNA: protein ratio (Cs, capacity for protein synthesis). In contrast to muscle, we found no significant variation in liver FSR between 2 and 4 wk of age. In addition, liver Cs and translational efficiencies were not decreased. Finally, in muscle as in liver, FBR did not show any clear age-related pattern.

Aging↗

PubMed1993

In-series fiber architecture in long human muscles.

The fiber architecture of adult human sartorius and gracilis muscles was examined using a combination of fiber microdissections and histological methods. Intact fibers were dissected from fascicles of muscle strips that were digested in nitric acid. All of these fibers terminate intrafascicularly by tapering to a fine strand at one or both ends. They measure 4-20 cm after correction for shrinkage. Systematic dissections of 1 cm long blocks sampled at intervals along the muscle length suggest that tapered fiber endings occur at all locations along the muscle but are most common centrally; here they accounted for up to 14% of dissected fibers in each block. Transverse sections of muscle confirm that fiber profiles with small diameters occur at all levels of the muscle but are especially common in sections more than 5 cm from its origin or insertion. The architectural arrangement demonstrated here suggests that long human muscles, like muscles in other species, are composed of relatively short, in-series fibers. This has many implications for the neural activation and force-developing behavior of these muscles that must be considered when paralyzed muscles are reanimated using electrical stimulation. Further, it may predispose long muscles to certain types of neuromuscular damage and dysfunction.

Adult↗

PubMed1999

An electrophoretic study of myosin heavy chain expression in skeletal muscles of the toad Bufo marinus.

In this study we developed an SDS-PAGE protocol which for the first time separates effectively all myosin heavy chain (MHC) isoforms expected to be expressed in iliofibularis (IF), pyriformis (PYR), cruralis (CRU) and sartorius (SAR) muscles of the toad Bufo marinus on the basis of previously reported fibre type composition. The main feature of the method is the use of alanine instead of glycine both in the separating gel and in the running buffer. The correlation between the MHC isoform composition of IF, SAR and PYR muscles determined in this study and the previously reported fibre type composition of IF and SAR muscles in the toad and of PYR muscle in the frog was used to tentatively identify the MHC isoforms expressed by twitch fibre types 1, 2 and 3 and by tonic fibres. The alanine-SDS electrophoretic method was employed to examine changes in the MHC composition of IF, PYR, CRU and SAR muscles with the ontogenetic growth of the toad from post-natal life (body weight < 1 g) to late adulthood (body weight 200-450 g). The developmental changes in the MHC isoform composition of the toad IF muscle observed in this study are in very good agreement with those in the fibre type composition of the developing IF muscle reported in the literature.

Animals↗