Fatigue in phasic and tonic fibers of frog muscle

Single isolated phasic muscle fibers and small bundles of tonic fibers were directly stimulated in one-per-second twitch series by massive electrode shocks. During the stimulation period the isometric tension developed by the phasic fiber continuously decreased, first rapidly and then slowly. The tonic fibers behaved similarly, but showed much less fatigue than the phasic ones. In general, recovery of the fibers after cessation of stimulation also occurred in two phases.     

Phosphate release and force generation in skeletal muscle fibers

Rapid laser pulse-induced photolysis of an adenosine triphosphate precursor in muscle fibers abruptly initiated cycling of the cross-bridges. The accompanying changes in tension and stiffness were related to elementary mechanochemical events of the energy-transducing mechanism. When inorganic phosphate was present at millimolar concentrations during liberation of adenosine triphosphate in the absence of calcium, relaxation was accelerated. Steady active tension in the presence of calcium was decreased but the approach to final tension was more rapid. These results suggest that, during energy transduction, formation of the dominant force-generating cross-bridge state is coupled to release of inorganic phosphate in a reaction that is readily reversible.     

Laser diffraction studies on single skeletal muscle fibers

Sarcomere movements during isometric tetanic contractions were resolved to 50 angstroms by diffraction techniques. After a latent period that followed the first stimulus, all sarcomeres shortened simultaneously and uniformly. Oscillations in length and tension in synchrony with the stimuli occurred during an incomplete tetanus. However, no oscillations in length were detected during the plateau of a tetanus.     

Calcium-sensitive cross-bridge transitions in mammalian fast and slow skeletal muscle fibers

The fundamental mechanism underlying the differing rates of tension development in fast and slow mammalian skeletal muscle is still unknown. Now, in skinned (membrane-permeabilized) single fibers it has been shown that the rate of formation of the strongly bound, force-producing cross-bridge between actin and myosin is calcium-sensitive in both fast and slow fibers and that the rate is markedly greater in fast fibers. The transition rates obtained at high calcium concentrations correlated with myosin isoform content, whereas at low calcium concentrations the thin filament regulatory proteins appeared to modulate the rate of tension development, especially in fast fibers. Fiber type-dependent differences in rates of cross-bridge transitions may account for the characteristic rates of tension development in mammalian fast and slow skeletal muscles.     

Sodium and potassium activities in normal and "sodium-rich" frog skeletal muscle

In frog sartorius muscles immersed for 2 hours at 26 degrees C in normal Ringer solution, the intrafiber potassium concentration, C(K)(in millimoles per liter), was 123 +/- 2 (mean value plus or minus standard error), and the potassium activity, a(K) (in millimoles per liter), was 90 +/- 1.0. The corresponding sodium concentration and activity were 20 +/- 1 and 6.5 +/- 0.4, respectively. After overnight immersion in K+-free Ringer solution the values were: CK, 97 +/- 2; aK, 81.5 +/- 1.6; CNa, 47 +/- 2; and aNa, 11.2 +/- 0.6. The changes in aK and aNa during storage were not consistent with an exchange between predominantly "free" fiber K+ and external Na+. These results suggest that the Na+ taken up during overnight immersion largely replaced adsorbed or sequestered K+ in the fibers.     

It is diprotonated inorganic phosphate that depresses force in skinned skeletal muscle fibers

The increases in the intracellular concentrations of inorganic phosphate and hydrogen ion accompanying fatigue of skeletal muscle appear to be the most important metabolic changes associated with the decrease in contractile force. Experiments on chemically skinned single fibers from rabbit psoas muscle with pH ranging between 6 and 7.25 demonstrate that the depression of maximal calcium-activated force by inorganic phosphate correlates nicely with the concentration of the acidic (diprotonated) species. Therefore, in addition to the well-known depressant effect on the contractile machinery of lowering pH per se, any decrease of intracellular pH associated with fatigue further depresses force production by converting more of the total inorganic phosphate within the cell to the inhibitory diprotonated form.     

Frog skeletal muscle fibers: changes in electrical properties after disruption of transverse tubular system

In muscle fibers which have been exposed for 1 hour to a Ringer solution containing 400 millimolar glycerol and then returned to plain Ringer solution, the transverse tubular system is disrupted. At the same time the membrane capacitance is markedly reduced and hyperpolarizing current pulses no longer produce a slow, progressive increase in potential (creep). The large capacitance of muscle and the phenomenon of "creep" must both depend on an intact transverse tubular system.     

Calcium dependence of the inactivation of calcium currents in skeletal muscle fibers of an insect

Calcium currents in skeletal muscle fibers of an insect, Carausius morosus, inactivate under depolarization. This inactivation depends on the current being carried across the membrane by calcium ions, rather than strontium or bariumions.     

Transverse tubular system in glycerol-treated skeletal muscle

Horseradish peroxidase used as an extracellular marker fills 98.5 percent of the central triadic elements (tubules) in normal muscle and 97.2 percent in muscle soaked in Ringer solution to which 400-millimolar glycerol is added. A glycerol-soaked muscle rapidly returned to normal Ringer solution has a disrupted transverse tubular system and has only 3.2 percent of triads filled with peroxidase.     

Ribonuclease-inhibitor system abnormality in dystrophic mouse skeletal muscle

Skeletal muscle extracts from mice with muscular dystrophy contain severalfold higher than normal levels of free alkaline ribonuclease II activity and none of the free ribonuclease inhibitor normally present. This abnormal pattern is not seen in heart or liver extracts from dystrophic mice.     

Length-force relation of calcium activated muscle fibers

Calcium activated skinned frog muscle fibers develop a large relative force at a sarcomere length of 1.0 micrometer. Since the normal myofilament lattice is perturbed at this length, regularity of the lattice does not appear to be an important factor in the contraction mechanism.     

猪心肌和骨骼肌miRNA转录组比较分析

【目的】研究microRNA(miRNA)在猪不同类型肌肉生长发育中的作用。【方法】以猪心肌以及2种骨骼肌(背最长肌和腰大肌)为材料,采用Illumina高通量测序技术鉴定其miRNA转录组,并进行差异表达分析和靶基因富集分析。【结果】从猪心肌、背最长肌和腰大肌组织的3个小RNA测序文库中共获得约56M的序列,通过生物信息分析共鉴定出907个非冗余miRNA,其中441个miRNA在3个文库共同表达,123个miRNA在文库间表现为显著的差异表达(P10-6)。对3个文库差异表达miRNA的相关性分析发现,背最长肌与腰大肌的相关性最高(r=0.94),证明2种骨骼肌的表达模式十分相近,而心肌与2种骨骼肌的表达模式不同。通过对各文库高表达的miRNA分析发现,表达量前十的miRNA中有6个miRNA的表达量在心肌中极显著上调。对在心肌内上调的6个miRNA进行的靶基因预测和生物学功能预测发现,这些差异miRNA主要靶向作用于钙信号通路和胰岛素信号通路。荧光定量PCR(qRT-PCR)验证结果表明高通量测序结果准确可靠。【结论】从miRNA层面揭示了猪心肌和骨骼肌的差异,这种差异在一定程度上印证了心肌和骨骼肌之间迥异的生理学特征。     

Mechanism of fibrillation potentials in denervated mammalian skeletal muscle

This report concerns the origin and mechanism of fibrillation potentials. It is proposed that these potentials do not necessarily arise from degenerated endplate organs. The precursor is the rhythmic oscillations of the membrane potential. This mechanism may also occur in the case of epileptic discharges from epileptic cells in the cerebral cortex.     

Regulation of mitochondrial biogenesis in skeletal muscle by CaMK

Endurance exercise training promotes mitochondrial biogenesis in skeletal muscle and enhances muscle oxidative capacity, but the signaling mechanisms involved are poorly understood. To investigate this adaptive process, we generated transgenic mice that selectively express in skeletal muscle a constitutively active form of calcium/calmodulin-dependent protein kinase IV (CaMKIV*). Skeletal muscles from these mice showed augmented mitochondrial DNA replication and mitochondrial biogenesis, up-regulation of mitochondrial enzymes involved in fatty acid metabolism and electron transport, and reduced susceptibility to fatigue during repetitive contractions. CaMK induced expression of peroxisome proliferator-activated receptor gamma coactivator 1 (PGC-1), a master regulator of mitochondrial biogenesis in vivo, and activated the PGC-1 gene promoter in cultured myocytes. Thus, a calcium-regulated signaling pathway controls mitochondrial biogenesis in mammalian cells.     

Histochemical phosphorylase activity in regenerating muscle fibers from myophosphorylase-deficient patients

Fresh frozen sections of mature skeletal muscle fibers from patients with genetically determined "absence" of skeletal muscle phosphorylase (McArdle's disease) have no histochemical phosphorylase activity. That regenerating muscle fibers, in vitro and in vivo, from such patients do have histochemical phosphorylase activity present suggests a loss of enzyme activity with fiber maturity.     

Histochemical abnormalities of skeletal muscle in patients with acute psychoses

In 29 acutely psychotic patients (mostly schizophrenic), histochemical abnormalities of a myopathic type were demonstrated in skeletal muscle biopsies from 13 and were generally correlated with elevation of the "muscle" type isoenzymes of creatine phosphokinase in the patients' serum. The incidence was much higher than found in normal controls, hospitalized neurotic psychiatric patients, or parents of acutely psychotic patients. A diazo-coupling type of "alka-line phosphatase" reaction was particularly useful in identifying abnormal muscle fibers.     

Crayfish muscle fiber: spike electrogenesis in fibers with long sarcomeres

Most of the muscle fibers in the walking legs of the crayfish Procambarus clarkii generate only graded electrical responses. However, some fibers in extensor muscles of the carpopodite have long sarcomeres, about 10 micrometers in length, and generate overshooting spikes that have conduction velocities of 0.3 meter per second. The spikes induce twitch contractions.     

Mobility of potassium ion in frog muscle cells, both living and dead

The diffusion coefficient of potassium ion (DK) in frog muscles was studied by a new method. In normal cytoplasm DK averaged one-eighth of the value in the free solution. Arrest of metabolism or injury caused an increase in DK. In muscles killed with iodoacetate, DK rose to three-quarters of the value in free solution. The data support the association-induction hypothesis.