Capillaries are Embedded in the Sarcolemma of Murine Slow Twitch Skeletal Muscle Fibers

Na current density and membrane capacitance were studied with the loose patch voltage clamp technique on rat fast- and slow-twitch skeletal muscle fibers at three different regions on the fibers: 1) the end plate border, 2) greater than 200 microns from the end plate (extrajunctional), and 3) on the end plate postsynaptic membrane. Fibers were treated with collagenase to improve visualization of the end plate and to enzymatically remove the nerve terminal. The capacitance of membrane patches was similar on fast- and slow-twitch fibers and patches of membrane on the end plate had twice the capacitance of patches elsewhere. For fast- and slow-twitch fibers, the sizes of the Na current normalized to the area of the patch were as follows: end plate greater than end plate border greater than extrajunctional. For both types of fibers, the amplitudes of the Na current normalized to the capacitance of the membrane patch were as follows: end plate approximately end plate border greater than extrajunctional. At each of the three regions, the Na current densities were larger on fast-twitch fibers and fast-twitch fibers had a larger increase in Na current density at the end plate border compared with extrajunctional membrane.

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Defective Acetylcholine Receptor Subunit Switch Precedes Atrophy of Slow-Twitch Skeletal Muscle Fibers Lacking ERK1/2 Kinases in Soleus Muscle

Scientific Reports ◽

10.1038/srep38745 ◽

2016 ◽

Vol 6 (1) ◽

Cited By ~ 5

Author(s):

Shuo Wang ◽

Bonnie Seaberg ◽

Ximena Paez-Colasante ◽

Mendell Rimer

Keyword(s):

Skeletal Muscle ◽

Acetylcholine Receptor ◽

Soleus Muscle ◽

Muscle Fibers ◽

Neuromuscular Synapse ◽

Fiber Morphology ◽

Skeletal Muscle Fibers ◽

Slow Twitch

Abstract To test the role of extracellular-signal regulated kinases 1 and 2 (ERK1/2) in slow-twitch, type 1 skeletal muscle fibers, we studied the soleus muscle in mice genetically deficient for myofiber ERK1/2. Young adult mutant soleus was drastically wasted, with highly atrophied type 1 fibers, denervation at most synaptic sites, induction of “fetal” acetylcholine receptor gamma subunit (AChRγ), reduction of “adult” AChRε, and impaired mitochondrial biogenesis and function. In weanlings, fiber morphology and mitochondrial markers were mostly normal, yet AChRγ upregulation and AChRε downregulation were observed. Synaptic sites with fetal AChRs in weanling muscle were ~3% in control and ~40% in mutants, with most of the latter on type 1 fibers. These results suggest that: (1) ERK1/2 are critical for slow-twitch fiber growth; (2) a defective γ/ε-AChR subunit switch, preferentially at synapses on slow fibers, precedes wasting of mutant soleus; (3) denervation is likely to drive this wasting, and (4) the neuromuscular synapse is a primary subcellular target for muscle ERK1/2 function in vivo.

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Activity-dependent nuclear translocation and intranuclear distribution of NFATc in adult skeletal muscle fibers

The Journal of Cell Biology ◽

10.1083/jcb.200103020 ◽

2001 ◽

Vol 155 (1) ◽

pp. 27-40 ◽

Cited By ~ 130

Author(s):

Yewei Liu ◽

Zoltán Cseresnyés ◽

William R. Randall ◽

Martin F. Schneider

Keyword(s):

Skeletal Muscle ◽

Electrical Stimulation ◽

Nuclear Translocation ◽

Fiber Type ◽

Muscle Fibers ◽

Adult Skeletal Muscle ◽

Skeletal Muscle Fibers ◽

Slow Twitch ◽

Nuclear Foci ◽

Fast Twitch

TTranscription factor nuclear factor of activated T cells NFATc (NFATc1, NFAT2) may contribute to slow-twitch skeletal muscle fiber type–specific gene expression. Green fluorescence protein (GFP) or FLAG fusion proteins of either wild-type or constitutively active mutant NFATc [NFATc(S→A)] were expressed in cultured adult mouse skeletal muscle fibers from flexor digitorum brevis (predominantly fast-twitch). Unstimulated fibers expressing NFATc(S→A) exhibited a distinct intranuclear pattern of NFATc foci. In unstimulated fibers expressing NFATc–GFP, fluorescence was localized at the sarcomeric z-lines and absent from nuclei. Electrical stimulation using activity patterns typical of slow-twitch muscle, either continuously at 10 Hz or in 5-s trains at 10 Hz every 50 s, caused cyclosporin A–sensitive appearance of fluorescent foci of NFATc–GFP in all nuclei. Fluorescence of nuclear foci increased during the first hour of stimulation and then remained constant during a second hour of stimulation. Kinase inhibitors and ionomycin caused appearance of nuclear foci of NFATc–GFP without electrical stimulation. Nuclear translocation of NFATc–GFP did not occur with either continuous 1 Hz stimulation or with the fast-twitch fiber activity pattern of 0.1-s trains at 50 Hz every 50 s. The stimulation pattern–dependent nuclear translocation of NFATc demonstrated here could thus contribute to fast-twitch to slow-twitch fiber type transformation.

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Coexistence of two calsequestrin isoforms in rabbit slow-twitch skeletal muscle fibers

FEBS Letters ◽

10.1016/0014-5793(92)80241-8 ◽

1992 ◽

Vol 299 (2) ◽

pp. 175-178 ◽

Cited By ~ 24

Author(s):

Donatella Biral ◽

Pompeo Volpe ◽

Ernesto Damiani ◽

Alfredo Margreth

Keyword(s):

Skeletal Muscle ◽

Muscle Fibers ◽

Skeletal Muscle Fibers ◽

Slow Twitch

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Myofibrillar regulatory mechanisms of stretch activation in mammalian striated muscle

10.32469/10355/63384 ◽

2017 ◽

Author(s):

◽

Joel C. Robinett

Keyword(s):

Skeletal Muscle ◽

Striated Muscle ◽

Muscle Fibers ◽

Stretch Activation ◽

Skeletal Muscle Fibers ◽

Slow Twitch ◽

Low Levels ◽

Slow Twitch Fibers ◽

Fast Twitch ◽

Transient Force

Stretch activation is described as a delayed increase in force after an imposed stretch. This process is essential in the flight muscles of many insects and is also observed, to some degree, in mammalian striated muscles. The mechanistic basis for stretch activation remains uncertain, although it appears to involve cooperative activation of the thin filaments (12, 80). The purpose of this study was to address myofibrillar regulatory mechanisms of stretch activation in mammalian striated muscle. For these studies, permeabilized rat slow-twitch and fast-twitch skeletal muscle fibers were mounted between a force transducer and motor, and a slack-re-stretch maneuver was performed over a range of Ca[superscript 2+] activation levels. Following slack-re-stretch there was a stretch activation process that often resulted in a transient force overshoot (P[subscript TO]), which was quantified relative to steady-state isometric force. P[subscript TO] was highly dependent upon Ca[superscript 2+] activation level, and the relative magnitude of P[subscript TO] was greater in slow-twitch fibers than fast-twitch fibers. In both slow-twitch and fast-twitch fibers, force redevelopment involved a fast, Ca[superscript 2+] activation dependent process (k1) and a slower, less activation dependent process (k2). Interestingly, the two processes converged at low levels of Ca[superscript 2+] activation in both fiber types. P[subscript TO] also contained a relaxation phase, which progressively slowed as Ca[superscript 2+] activation levels increased and was more Ca[superscript 2+] activation dependent in slow-twitch fibers. These results suggest that stretch activation may not be solely regulated by the extent of apparent cooperative activation of force due to a higher relative level of stretch activation in the less cooperative slow-twitch skeletal muscle fiber. Next, we investigated an additional potential molecular mechanism by regulating stretch activation in mammalian striated muscle. Along these lines, our lab has previously observed that PKA-induced phosphorylation of cMyBP-C and cTnI elicited a significant increase in transient force overshoot following slack-re-stretch maneuver in permeabilized cardiac myocytes (29). Interestingly, in slow-twitch skeletal muscle fibers MyBP-C but not ssTnI is phosphorylated by PKA (28). We, thus, took advantage of this variation in substrates phosphorylated by PKA to investigate the effects of PKA-induced phosphorylation of MyBP-C on stretch activation in slow-twitch skeletal muscle fibers. Following PKA treatment of skinned slow-twitch skeletal muscle fibers, the magnitude of P[subscript TO] more than doubled, but this only occurred at low levels of Ca[superscript 2+] activation (i.e., [approximately]25% maximal Ca[superscript 2+] activated force). Also, force redevelopment rates were significantly increased over the entire range of Ca[superscript 2+] activation levels following PKA treatment. In a similar manner, force decay rates showed a tendency of being faster following PKA treatment, however, were only statistically significantly faster at 50% Ca[superscript 2+] activation. Overall, these results are consistent with a model whereby stretch transiently increases the number of cross-bridges made available for force generation and PKA phosphorylation of MyBP-C enhances these stretch activation processes.

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Erratum: Corrigendum: Defective Acetylcholine Receptor Subunit Switch Precedes Atrophy of Slow-Twitch Skeletal Muscle Fibers Lacking ERK1/2 Kinases in Soleus Muscle

Scientific Reports ◽

10.1038/srep45420 ◽

2017 ◽

Vol 7 (1) ◽

Author(s):

Shuo Wang ◽

Bonnie Seaberg ◽

Ximena Paez-Colasante ◽

Mendell Rimer

Keyword(s):

Skeletal Muscle ◽

Acetylcholine Receptor ◽

Soleus Muscle ◽

Muscle Fibers ◽

Receptor Subunit ◽

Skeletal Muscle Fibers ◽

Slow Twitch

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Sequential effects of GSNO and H2O2 on the Ca2+ sensitivity of the contractile apparatus of fast- and slow-twitch skeletal muscle fibers from the rat

AJP Cell Physiology ◽

10.1152/ajpcell.00251.2008 ◽

2009 ◽

Vol 296 (5) ◽

pp. C1015-C1023 ◽

Cited By ~ 19

Author(s):

Timothy Spencer ◽

Giuseppe S. Posterino

Keyword(s):

Skeletal Muscle ◽

Fiber Type ◽

Muscle Fibers ◽

Contractile Apparatus ◽

Sequential Effects ◽

No Donor ◽

Skeletal Muscle Fibers ◽

Slow Twitch ◽

The Individual ◽

Fast Twitch

Reactive oxygen species (ROS), such as hydrogen peroxide (H2O2) and nitric oxide (NO), have been shown to differentially alter the Ca2+ sensitivity of the contractile apparatus of fast-twitch skeletal muscle, leading to the proposal that normal muscle function is controlled by perturbations in the amounts of these two groups of molecules ( 28 ). However, no previous studies have examined whether these opposing actions are retained when the contractile apparatus is subjected to both molecule types. Using mechanically skinned fast- and slow-twitch skeletal muscle fibers of the rat, we compared the effects of sequential addition of nitrosoglutathione (GSNO), a NO donor, and H2O2 on the Ca2+ sensitivity of the contractile apparatus. As expected from previous reports in fast-twitch fibers, when added separately, GSNO (1 mM) reduced the Ca2+ sensitivity of the contractile apparatus, whereas H2O2 (10 mM; added during contractions) increased the Ca2+ sensitivity of the contractile apparatus. When added sequentially to the same fiber, such that the oxidation by one molecule (e.g., GSNO) preceded the oxidation by the other (e.g., H2O2), and vice versa, the individual effects of both molecules on the Ca2+ sensitivity were retained. Interestingly, neither molecule had any effect on the Ca2+ sensitivity of slow-twitch skeletal muscle. The data show that H2O2 and GSNO retain the capacity to independently affect the contractile apparatus to modulate force. Furthermore, the absence of effects in slow-twitch muscle may further explain why this fiber type is relatively insensitive to fatigue.

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Regulation of Ca2+ handling by phosphorylation status in mouse fast- and slow-twitch skeletal muscle fibers

AJP Cell Physiology ◽

10.1152/ajpcell.1997.273.6.c1915 ◽

1997 ◽

Vol 273 (6) ◽

pp. C1915-C1924 ◽

Cited By ~ 38

Author(s):

Yewei Liu ◽

Evangelia G. Kranias ◽

Martin F. Schneider

Keyword(s):

Skeletal Muscle ◽

Muscle Fibers ◽

Wild Type ◽

Decay Rate Constant ◽

Single Action ◽

Cyclic Monophosphate ◽

Skeletal Muscle Fibers ◽

Intracellular Ca ◽

Flexor Digitorum Brevis ◽

Slow Twitch

The effects of phosphorylation status on Ca2+release and Ca2+ removal were studied in fast-twitch flexor digitorum brevis and slow-twitch soleus skeletal muscle fibers enzymatically isolated from wild-type and phospholamban knockout (PLBko) mice. In all fibers the adenosine 3′,5′-cyclic monophosphate-dependent protein kinase (PKA) inhibitor H-89 decreased the peak amplitude of the intracellular Ca2+ concentration ([Ca2+]) transient for a single action potential, and the PKA activator dibutyryl adenosine 3′,5′-cyclic monophosphate (DBcAMP) reversed this effect, indicating modulation of Ca2+release by phosphorylation status in all fibers. H-89 decreased the decay rate constant of the [Ca2+] transient and DBcAMP reversed this effect only in phospholamban-expressing fibers (wild-type soleus), indicating modulation of Ca2+ removal only in the presence of phospholamban. A high basal level of PKA phosphorylation in soleus fibers maintained under our control conditions was indicated by the lack of effect of direct application of DBcAMP on Ca2+ release or Ca2+ removal in wild-type or PLBko soleus fibers and was confirmed by analysis of phospholamban from wild-type soleus fibers.

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The “KIMWIPE” Effect in Ultra-Thin Cryosections

Proceedings, annual meeting, Electron Microscopy Society of America ◽

10.1017/s0424820100119119 ◽

1985 ◽

Vol 43 ◽

pp. 458-459

Author(s):

I. Taylor ◽

P. Ingram ◽

J.R. Sommer

Keyword(s):

Skeletal Muscle ◽

Electrical Stimulation ◽

Muscle Fibers ◽

Ice Crystals ◽

Crystal Formation ◽

Ice Crystal ◽

Thin Sections ◽

Skeletal Muscle Fibers ◽

Freeze Dried ◽

Ice Crystal Formation

In studying quick-frozen single intact skeletal muscle fibers for structural and microchemical alterations that occur milliseconds, and fractions thereof, after electrical stimulation, we have developed a method to compare, directly, ice crystal formation in freeze-substituted thin sections adjacent to all, and beneath the last, freeze-dried cryosections. We have observed images in the cryosections that to our knowledge have not been published heretofore (Figs.1-4). The main features are that isolated, sometimes large regions of the sections appear hazy and have much less contrast than adjacent regions. Sometimes within the hazy regions there are smaller areas that appear crinkled and have much more contrast. We have also observed that while the hazy areas remain still, the regions of higher contrast visibly contract in the beam, often causing tears in the sections that are clearly not caused by ice crystals (Fig.3, arrows).

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Effect of External Calcium and other Divalent Cations on K+ Contractures in Denervated Slow Skeletal Muscle Fibers of the Frog

Journal of Biomedical and Allied Research ◽

10.37191/mapsci-2582-4937-1(2)-009 ◽

2019 ◽

Author(s):

Leonardo Hernández

Keyword(s):

Skeletal Muscle ◽

Binding Capacity ◽

Divalent Cations ◽

Muscle Fibers ◽

Free Calcium ◽

Slow Skeletal Muscle ◽

Skeletal Muscle Fibers ◽

Free Calcium Concentration ◽

Chronic Denervation ◽

Denervated Muscles

The influence of Ca2+ and other divalent cations on contractile responses of slow skeletal muscle fibers of the frog (Rana pipiens) under conditions of chronic denervation was investigated.Isometric tension was recorded from slow bundles of normal and denervated cruralis muscle in normal solution and in solutions with free calcium concentration solution or in solutions where other divalent cations (Sr2+, Ni2+, Co2+ or Mn2+) substituted for calcium. In the second week after nerve section, in Ca2+-free solutions, we observed that contractures (evoked from 40 to 80 mM-K+) of non-denervated muscles showed significantly higher tensions (p<0.05), than those from denervated bundles. Likewise, in solutions where calcium was substituted by all divalent cations tested, with exception of Mn2+, the denervated bundles displayed lower tension than non-denervated, also in the second week of denervation. In this case, the Ca2+ substitution by Sr2+ caused the higher decrease in tension, followed by Co2+ and Ni2+, which were different to non-denervated bundles, as the lowest tension was developed by Mn2+, followed by Co2+, and then Ni2+ and Sr2+. After the third week, we observed a recovery in tension. These results suggest that denervation altering the binding capacity to divalent cations of the voltage sensor.

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