Factors causing different properties at neuromuscular junctions in fast and slow rat skeletal muscles

Wærhaug, O.; Lømo, Terje

doi:10.1007/bf00193409

Cited by 34 publications

(33 citation statements)

References 52 publications

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“…Thus, in the rat, synaptic area is greater in soleus slow fibers than in EDL fast fibers (839,874), but the ratio between NMJ area and fiber size is very similar in both muscles. The size of the vesicular pool is accordingly larger in soleus than in EDL.…”

Section: Transmission Of Nerve Impulse To Muscle Fibersmentioning

confidence: 85%

Fiber Types in Mammalian Skeletal Muscles

Schiaffino

Reggiani

2011

Physiological Reviews

2,324

2,465

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Mammalian skeletal muscle comprises different fiber types, whose identity is first established during embryonic development by intrinsic myogenic control mechanisms and is later modulated by neural and hormonal factors. The relative proportion of the different fiber types varies strikingly between species, and in humans shows significant variability between individuals. Myosin heavy chain isoforms, whose complete inventory and expression pattern are now available, provide a useful marker for fiber types, both for the four major forms present in trunk and limb muscles and the minor forms present in head and neck muscles. However, muscle fiber diversity involves all functional muscle cell compartments, including membrane excitation, excitation-contraction coupling, contractile machinery, cytoskeleton scaffold, and energy supply systems. Variations within each compartment are limited by the need of matching fiber type properties between different compartments. Nerve activity is a major control mechanism of the fiber type profile, and multiple signaling pathways are implicated in activity-dependent changes of muscle fibers. The characterization of these pathways is raising increasing interest in clinical medicine, given the potentially beneficial effects of muscle fiber type switching in the prevention and treatment of metabolic diseases.

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Section: Transmission Of Nerve Impulse To Muscle Fibersmentioning

confidence: 85%

Fiber Types in Mammalian Skeletal Muscles

Schiaffino

Reggiani

2011

Physiological Reviews

2,324

2,465

View full text Add to dashboard Cite

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“…Limb muscles differ substantially in activation history, functional demands, and contraction patterns. 5,6,42 Thus, reported differences in function at the neuromuscular junction may reflect influences other than specific effects of motor units, including differences in muscle loading, activation history, and synaptic input. 26,27 In this regard, the study of a single muscle of mixed fiber-type composition may elucidate fiber type-specific differences in neuromuscular transmission.…”

Section: Discussionmentioning

confidence: 93%

Synaptic vesicle cycling at type‐identified diaphragm neuromuscular junctions

et al. 2004

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Differences in neuromuscular transmission and neuromuscular junction morphology exist across muscle fiber types. We hypothesized that these fiber-type differences are reflected in the size of the cycling synaptic vesicle pool. Synaptic vesicle cycling at type-identified rat diaphragm neuromuscular junctions was examined by fluorescently labeling presynaptic vesicles with FM4-64. We found that FM4-64 fluorescence uptake was higher at presynaptic terminals of type I/IIa fibers than type IIx/IIb fibers. However, no fiber-type differences in the rate of FM4-64 destaining were found with repetitive nerve stimulation. Synaptic vesicle density at active zones was examined by transmission electron microscopy. In accordance with FM4-64 uptake, synaptic vesicle density was greater at type I/IIa than IIx/IIb fibers. These results demonstrate differences in synaptic vesicle cycling across diaphragm muscle fiber types, which may underlie previously observed differences in neuromuscular transmission across diaphragm muscle fiber types. In the diaphragm, motor units comprising type I and type IIa fibers are most frequently recruited with a duty cycle of approximately 40%. Motor units comprising IIx/IIb fibers are infrequently recruited and only for short durations. The capacity for synaptic vesicle release and cycling at different muscle fiber types matches the functional requirements of these motor units. If the demand for recruitment of motor units comprising IIx/IIb fibers increases, for example, with mechanical loading, there is an increased risk for neuromuscular transmission failure that my relate to the capacity for synaptic vesicle release and cycling. Muscle fiber type-specific adaptations should be considered when examining neuromuscular disorders.

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“…Therefore, in the present study, the total numbers of both quiescent and mitotically active satellite cells, as well as the myonuclear number, were counted in whole fibers with central versus peripheral myonuclei. Waerhaug and Lomo [1994] reported that fast motoneurons form large ectopic junctions, whereas slow motoneurons form small ectopic junctions, concluding that the type of motoneuron, not muscle fiber, determines the fast or slow character of the neuromuscular junction (NMJ). Changes in the distribution of acetylcholine receptors were also observed in muscle fibers of mdx mice [Torres and Duchen, 1987;Lyons and Slater, 1991;Minatel et al, 2001;Personius and Sawyer, 2005].…”

Section: Introductionmentioning

confidence: 99%

Myonucleus-Related Properties in Soleus Muscle Fibers of <i>mdx</i> Mice

Terada

Lan

Kawano

et al. 2009

Cells Tissues Organs

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Distribution and total number of myonuclei in single soleus muscle fibers, sampled from tendon to tendon, were analyzed in mdx and wild-type (WT) mice. Apoptotic myonuclei and the microscopic structure around the myonuclei were also analyzed. Three types of muscle fibers of mdx mice with myonuclear distribution at either central, peripheral, or both central and peripheral regions were observed in the longitudinal analyses. All of the myonuclei were located at the peripheral region in WT mice. The total number of myonuclei counted in the whole length of fibers with peripheral myonuclei only was 17% less in mdx than in WT mice (p < 0.05). But the total myonuclear numbers in mdx mouse fibers with different distribution (peripheral vs. central) of myonuclei were identical, and the peripheral nucleus was noted where the central nucleus was missing. Myonuclei located between the center and peripheral regions were also seen in the cross-sectional analyses of muscle fibers. The cross-sectional area and length of fibers, sarcomere number, myonuclear size, myosin heavy chain expression, satellite cell number and neuromuscular junction were identical between each type of fiber. Apoptosis was not detected in any myonuclei located either in central or peripheral regions of muscle fibers. Thus, it was suggested that apoptosis-related loss of central myonuclei and regeneration-related new accretion at the peripheral region is not the cause of different distribution of myonuclei seen in muscle fibers in mdx mice. However, it was speculated that cross-sectional migration of myonuclei from central to peripheral regions may be induced in response to regeneration, because the total myonuclear numbers in fibers with different distribution of myonuclei were identical, and the peripheral nucleus was noted where the central nucleus was missing. Further, myonuclei located between the center and peripheral regions were also seen. However, the question remains as to how or why nuclei might migrate to the periphery in a regenerating muscle fiber, since there was no microscopic evidence of any structural changes around the myonuclei that may be responsible for the movement of the nucleus.

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Factors causing different properties at neuromuscular junctions in fast and slow rat skeletal muscles

Cited by 34 publications

References 52 publications

Fiber Types in Mammalian Skeletal Muscles

Fiber Types in Mammalian Skeletal Muscles

Synaptic vesicle cycling at type‐identified diaphragm neuromuscular junctions

Myonucleus-Related Properties in Soleus Muscle Fibers of <i>mdx</i> Mice

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