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PubMed2026

Muscular fiber properties and multi-omics investigation of larval and adult locomotor muscle in Microhyla fissipes.

During metamorphosis, Microhyla fissipes undergoes a critical transition from an aquatic to a terrestrial lifestyle, accompanied by significant remodeling of skeletal muscle. Notably, larval tail muscle degenerates, while adult hindlimb muscle develops. However, the molecular mechanisms that orchestrate these muscle type-specific adaptations to the changing environment remain unclear. In this study, histological observation, transcriptomics, and metabolomics were integrated to compare locomotor muscles from two stages: larval muscle from tail versus adult muscle from hindlimb. Our results revealed that adult muscle fibers exhibited reduced diameter and shorter sarcomere length compared to those of tadpoles. Transcriptomic analysis identified 4103 differentially expressed genes (DEGs), including 2182 up-regulated and 1921 down-regulated genes. Up-regulated genes were mainly involved in energy metabolism and cellular homeostasis pathways, including PPAR signaling and oxidative phosphorylation, whereas down-regulated genes were associated with carbohydrate metabolism and cell proliferation pathways, such as glycolysis/gluconeogenesis and PI3K-Akt signaling. Metabolic profiling indicated a metabolic shift from anaerobic to aerobic energy production, with 57 differential metabolites identified, mainly involved in protein metabolism and insulin-related pathways. Integrated multi-omics analysis further highlighted the AMPK and FoxO signaling pathways play key roles in this process. In conclusion, our findings demonstrate that the metabolic and structural differences between larval and adult skeletal muscles are mediated by AMPK- and FoxO-dependent signaling pathways, providing novel insights into the molecular mechanisms underlying adaptive development and locomotor transition in anuran amphibians.

Animals↗
PubMed1979

[Electrogenesis of muscular fibers in the rat masseter muscle proper].

It was established by the method of intracellular lead of membrane rest potentials (MRP) and action potentials (AP) that fibers with high MRP and little overshot are mainly located in superficial layers of the rat masseter muscle proper whereas those with low MRP and high overshot principally in deep layers. Excitability of the cytoplasmic membrane of muscular fibers of both types proved to be related in electrical properties (critical level of depolarization, current threshold). It is suggested that the rat masseter muscle contains a great number of rapid phasic fibers in superficial layers and slow ones in deep layers.

Action Potentials↗
PubMed1979

Mechanical properties of the mammalian vas deferens. I. In the passive state.

Knowledge of the mechanical properties of the vas deferens is important in order to understand the mechanical interaction between an intravasal device (IVD) and the vas deferens--a necessary step for successful long-term implantation. It is equally important in order to understand the mechanism of sperm transport through the vas, with or without an IVD implant, by means of quantitative mechanical models. Experiments were performed, in vitro, on vas deferens from rat, bull, and rabbit, to determine its mechanical properties in the passive state. The data consist of (1) load response to simple extension and cyclic extension, (2) extensional response to cyclic loading, and (3) stress relaxation response at constant extensions. The load-elongation behavior is characterized by Fung's exponential model T = (T* + beta)e alpha(lambda-lambda*) - beta quantitatively, where T is the Lagrangian or engineering stress (current force in the specimen divided by the original area of cross section) (dyn/cm2), T* is a convenient stress value (dyn/cm2), alpha is a parameter characterizing material elasticity (dimensionless), beta is a second material parameter (dyn/cm2), lambda is a stretch ratio (dimensionless) equal to l/l0, where l is the instantaneous length of the specimen (cm) and l0 is its reference length measured at 2-gram-force (1 gram force = 981 dyn) applied load (cm), and lambda* is the stretch level corresponding to T* (dimensionless). The vas appears to behave as a viscoelastic material and its reduced relaxation function may be dependent on the initial level of stretch. The cyclic-loading and cyclic-extension data give evidence of internal damping mechanisms, which make the loading curves different from the unloading curves (hysteresis). Also, the mechanical behavior of the vas is found to be altered by repeated loadings in quick succession. It is likely that cyclic loadings, in vivo, occur at much lower levels of stress and thus cause negligible damage, or that there are natural mechanisms which repair the damage. The behavior of tissue from different species of animals are qualitatively similar, although the tissue from the larger-size animal is likely to be stronger and stiffer. Due to very little interweaving between the muscle fibers of the longitudinal and circumferential layers, the data reported reflect the properties of the longitudinal layers only. Because the muscular structure of the three layers is very similar, the properties of the circumferential layer may be extrapolated.

Animals↗
PubMed1978

Ultrastructure and mechanical activity expressed by striated muscle in culture.

Newly devised assay procedures for quantitating the mechanical capabilities of striated muscle fibers grown in cell culture have permitted the correlation of cytological features with the ability to respond mechanically to electrical and chemical stimuli during development. By developmental timing and by physiological characteristics, three distinct mechanical activities can be distinguished: : TWITCH, contracture and wave propagation (escalation). Parallel electron microscopy studies suggest that contracture and escalation require significantly greater internal membrane development than twitch. The assay procedures have revealed that fibers developed in culture from genetically dystrophic chick muscle cells display a heightened electrical threshold for a twich response, but are otherwise similar to normal fibers. Cultured chick fibers, whether of leg or breast origin, exhibit similar ultrastructural and mechanical properties; yet these are different from those of in vivo adult muscle and may represent the avian striated muscle archetype expressed in the absence of innervation. Primary or cell line cultures of rat muscle produce far fewer mechanically active fibers than do avian cell cultures. The influence of culture conditions and cell source, whether avian or mammalian, on the extent of differentiation expressed in culture is so great that our understanding of studies on cultured muscle fibers would benefit from some characterization of both morphological and contractile properties of the fibers being used.

Acetylcholine↗
PubMedDate not supplied

Electrophysiologic properties of intercostal muscle fibers in human neuromuscular diseases.

Electrophysiologic properties of biopsied normal and diseased intercostal muscle fibers were examined using intracellular microelectrode techniques. The resting potentials of all diseased muscle fibers were found to be depolarized. Those from Duchenne dystrophy patients showed the largest depolarization, followed by those from patients with myotonic muscular dystrophy, myotonia congenita, and motor neuron disease. All of the diseased fibers except those from myotonia congenita patients demonstrated an imparied ability to generate action potentials. In the latter fibers, the higher-than-normal membrane resistance was associated with hyperexcitability. When the membrane was hyperpolarized to the normal range, however, action potential characteristics in all fibers were near normal, except in motor neuron disease. All action potentials were blocked by tetrodotoxin. These findings--i.e., that all fibers were capable of generating action potentials when hyperpolarized, and that all action potentials were blocked by tetrodotoxin--suggest the relative intactness, in the disease studied here of the regenerative sodium conductance mechanism.

Action Potentials↗
PubMed1979

Stereologic analysis of dystrophic chicken muscle.

Stereologic methods have been used to estimate the volume and surface densities of sarcoplasmic reticulum (SR) and T tubules of normal and dystrophic chicken pectoralis muscle fibers. The surface and volume densities of the T system in dystrophic muscle fibers showed large increases compared with normal muscle fibers; the surface and volume densities of the SR showed large decreases. In addition, the SR and T system in dystrophic fibers undergo changes in shape. The tubules of the free SR become much narrower; the T system becomes dilated and vesiculated. Dystrophic fibers, on the average, are much larger than normal but maintain the same sarcolemmal surface/fiber volume ratio as normal fibers. Alterations in the surface and volume densities of the dystrophic sarcotubular system may account for some of the altered contractile properties of these muscles.

Animals↗
PubMed1979

Suppression of myotonia in dystrophic chicken muscle by phenytoin.

We describe myotonic electromyographic activity in muscles of genetically dystrophic chickens and show that this activity is antagonized in vivo by doses of phenytoin (DPH) that improve righting ability. To test the possibility that the in vivo effects of DPH can be accounted for by a direct action on skeletal muscle we studied posterior latissimus dorsi fibers in vitro at 23 degrees C with intracellular microelectrodes. Compared to normal fibers, fibers from untreated dystrophic chicks had larger diameters, increased membrane capacitance, longer latencies at rheobase, and a greater tendency to fire repetitively in response to direct stimulation. DPH (10 or 50 micrograms/ml in the bath solution) decreased latencies at rheobase and repetitive firing in fibers from untreated chicks. In DPH-free solution fibers from dystrophic chicks treated chronically with DPH were still abnormal with respect to latencies at rheobase and ease of repetitive firing. The data support the hypothesis that abnormalities of membrane electrical properties are major features of dystrophic chicken muscles and furthermore, show that DPH suppresses, but does not abolish, these abnormalities.

Animals↗
PubMedDate not supplied

[Synaptic ion currents in muscle fibers of Drosophila melanogaster].

The spontaneous excitatory junctional currents (e. j. c.'s) were recorded intracellulary using voltage clamp technique in experiments performed on the isolated cutaneo-muscle bag of larvae, early pupae stadium and adult fly Drosophila melanogaster. The fast miniature e. j. c.'s with mean amplitude 0.41 nA, rise time 1.60 ms and half-decay time 3.11 ms were most frequently observed. Besides these, slow miniature (half--decay time 7--20 ms) and fast giant (amplitude 12--15 nA) were sometimes present. It was found that the time course of fast e. j. c.'s is prolonged with hyperpolarisation and with the decrease in temperature. Some drugs which effectively modify the time course of end-plate currents at the cholinergic junctions (atropine, scopolamine, lidocaine, serotonin, QX-222 and ethanol) were tested. Except for ethanol, none of these drugs when added to the muscle bath affected either the amplitude or the time course of e. j. c.'s. The properties of e. j. c.'s in different neuro-muscular junctions of vertebrates and insects are discussed.

Animals↗
PubMed1976

[Muscle spindles in denervated and reinnervated m. soleus of the rat. II. Changes in the extra- and intrafusal muscle fibers].

After a transient or permanent unilateral denervation of the soleus muscle of the rat changes were investigated of extra- and intrafusal muscle fibres of the denervated (reinnervated) muscle as well as its contralateral still innervated muscle. Those data which were obtained from normal muscles of uninjured rats served as control. The changes of permanent denervated muscles were clear and statistically significant. The extrafusal muscle fibres show a considerable atrophy. The nuclear-chain fibres exhibit a decrease of their calibres. The extent of this atrophy is not as pronounced as in extrafusal muscle fibres. The nuclear-bag fibres show 12 weeks after denervation a small atrophy (or pseudoatrophy) and 18 weeks after denervation a significant hypertrophy. At the same time the number of nuclear-bag fibres is increasing. Besides the increase in number of intrafusal muscle fibres per muscle spindle, a change is observed of proportion of both intrafusal fibre types in favour of nuclear-bag fibres. The hypertrophy and the increase in number of the nuclear-bag fibres are discussed in connection with their functional properties.

Animals↗