Sarcomeric oscillations in frog skeletal muscle fibers

Brief asynchronous, small-amplitude, cyclic, longitudinal displacements of the striations of frog skeletal muscle fibers were observed with ordinary light microscopy after application of caffeine and certain quaternary ammonium compounds. With time these oscillations became synchronized and evolved into peristaltic-like movements. The oscillations were influenced by sarcomere length, temperature, external concentration of calcium ions, membrane potential, and disruption of the transverse tubules.     

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.     

Myosin light chain phosphorylation does not modulate cross-bridge cycling rate in mouse skeletal muscle

An attempt was made to determine whether phosphorylation of the myosin light chain represents a thick filament-associated mechanism for modulating the rate of cross-bridge cycling in mouse skeletal muscle. When the degree of light chain phosphorylation was varied independently of tetanus duration, there was no correlation of phosphorylation with cross-bridge turnover rate, as measured by the shortening velocity of the muscle. It is concluded that in intact skeletal muscle phosphorylation of the myosin light chain does not in itself modulate cross-bridge cycling rate and that previously reported changes in cycling rate were due to other factors that may vary with tetanus duration.     

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.     

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.     

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.     

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.     

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.     

Acetylcholine: fast axoplasmic transport in insect chemoreceptor fibers

Acetylcholine is transported along insect chemoreceptor axons at a rate of 12 to 13 centimeters per day after peripheral uptake of choline. Colchicine, vinblastine sulfate, and cytochalasin B all block transport, but transport continues in axons separated surgically from the cell body. These data from an insect are in accord with many studies on vertebrates which have implicated intracellular microtubules in the transport mechanism. The peripheral uptake of choline and its acetylation and transport to nerve terminals in the brain are consistent withthe suggestion that acetylcholine is an antennal sensory transmitter in insects.     

Hemoglobin adaptation for fast and slow water habitats in sympatric catostomid fishes

The oxygen equilibria of Catostomus insignis hemoglobins are pH dependent. Catostomus clarkii hemoglobins have some components (20 percent) whose oxygen equilibria are independent of pH because the alpha chains have NH(2)-termini that are blocked and the beta chains lack the "usual" COOH-terminal histidine. Since the Bohr effect is normally a beneficial phenomenon, the maintenance of some hemoglobins without a Bohr effect must provide a physiological advantage that is habitat specific. The intrastream ecological preferences of these sympatric catostomids suggest that the hemoglobins without the Bohr effect confer an ecological advantage in a swift water habitat.     

Fast transport system of materials in mammalian nerve fibers

A fast transport system of materials is shown in cat sensory fibers of sciatic nerve. After injection of tritiated leucine into the lumbar seventh ganglia, the distribution of activity was measured in the sciatic nerves from 2 to 8 hours afterward. The distribution showed a crest of activity advancing down the fibers at a rate of approximately 410 millimeters per day. An intraaxonic locus of the activity was indicated by a block of the downflow induced by local freezing which causes the fibers to close off. Some of the activity in the nerve was due to free tritiated leucine, with most of it incorporated into polypeptide, soluble protein, and subcellular particulates.     

Interlinked fast and slow positive feedback loops drive reliable cell decisions

Positive feedback is a ubiquitous signal transduction motif that allows systems to convert graded inputs into decisive, all-or-none outputs. Here we investigate why the positive feedback switches that regulate polarization of budding yeast, calcium signaling, Xenopus oocyte maturation, and various other processes use multiple interlinked loops rather than single positive feedback loops. Mathematical simulations revealed that linking fast and slow positive feedback loops creates a "dual-time" switch that is both rapidly inducible and resistant to noise in the upstream signaling system.     

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.     

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.     

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。     

Chemically induced fast solid-state transitions of omega-VOPO4 in vanadium phosphate catalysts

Vanadium phosphates are important catalysts for the oxidation of alkanes, and commercial catalysts comprise a complex range of V4+ and V5+ phosphates. We used three complementary in situ characterization methodologies-powder x-ray diffraction and laser Raman and electron paramagnetic resonance spectroscopies-to show that the metastable phase omega-VOPO4 is very sensitive to many of the reactants and products of butane oxidation. A rapid transformation from omega-VOPO4 to delta-VOPO4 occurs on exposure to butane at the reaction temperature, and hence the metastable omega-VOPO4 may play a role in the formation of commercial catalysts.     

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.     

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.