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

2001 ◽  
Vol 155 (1) ◽  
pp. 27-40 ◽  
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.

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

2009 ◽  
Vol 296 (5) ◽  
pp. C1015-C1023 ◽  
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.

Na current density at and away from end plates on rat fast- and slow-twitch skeletal muscle fibers

1992 ◽  
Vol 262 (1) ◽  
pp. C229-C234 ◽  
Author(s):  
R. L. Ruff
Keyword(s):  
Skeletal Muscle ◽  
Current Density ◽  
Muscle Fibers ◽  
Postsynaptic Membrane ◽  
Na Current ◽  
End Plate ◽  
Skeletal Muscle Fibers ◽  
Slow Twitch ◽  
Slow Twitch Fibers ◽  
Fast Twitch

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.

scholarly journals Activity- and Calcineurin-independent Nuclear Shuttling of NFATc1, but Not NFATc3, in Adult Skeletal Muscle Fibers

2006 ◽  
Vol 17 (4) ◽  
pp. 1570-1582 ◽  
Author(s):  
Tiansheng Shen ◽  
Yewei Liu ◽  
Zoltán Cseresnyés ◽  
Arie Hawkins ◽  
William R. Randall ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Electrical Stimulation ◽  
Nuclear Export ◽  
Muscle Fibers ◽  
Nuclear Accumulation ◽  
Leptomycin B ◽  
Adult Skeletal Muscle ◽  
Casein Kinase 1 ◽  
Nuclear Uptake ◽  
Skeletal Muscle Fibers

The transcription factor NFATc1 may be involved in slow skeletal muscle gene expression. NFATc1 translocates from cytoplasm to nuclei during slow fiber type electrical stimulation of skeletal muscle fibers because of activation of the Ca2+-dependent phosphatase calcineurin, resulting in nuclear factor of activated T-cells (NFAT) dephosphorylation and consequent exposure of its nuclear localization signal. Here, we find that unstimulated adult skeletal muscle fibers exhibit a previously unanticipated nucleocytoplasmic shuttling of NFATc1 without appreciable nuclear accumulation. In resting fibers, the nuclear export inhibitor leptomycin B caused nuclear accumulation of NFATc1 (but not of isoform NFATc3) and formation of NFATc1 intranuclear bodies independent of calcineurin. The rate of nuclear uptake of NFATc1 was 4.6 times lower in resting fibers exposed to leptomycin B than during electrical stimulation. Inhibitors of glycogen synthase kinase and protein kinase A or of casein kinase 1 slowed the decay of nuclear NFATc1 after electrical stimulation, but they did not cause NFATc1 nuclear uptake in unstimulated fibers. We propose that two nuclear translocation pathways, one pathway mediated by calcineurin activation and NFAT dephosphorylation and the other pathway independent of calcineurin and possibly independent of NFAT dephosphorylation, determine the distribution of NFATc1 between cytoplasm and nuclei in adult skeletal muscle.

scholarly journals Localization and Regulation of the N Terminal Splice Variant of PGC-1αin Adult Skeletal Muscle Fibers

2012 ◽  
Vol 2012 ◽  
pp. 1-8 ◽  
Author(s):  
Tiansheng Shen ◽  
Yewei Liu ◽  
Martin F. Schneider
Keyword(s):  
Skeletal Muscle ◽  
Splice Variant ◽  
Nuclear Export ◽  
Fiber Type ◽  
Muscle Fibers ◽  
Nuclear Accumulation ◽  
Peroxisome Proliferator ◽  
Peroxisome Proliferator Activated Receptor ◽  
Adult Skeletal Muscle ◽  
Skeletal Muscle Fibers

The transcriptional coactivator peroxisome proliferator-activated receptorγcoactivator 1α(PGC-1α) regulates expression of genes for metabolism and muscle fiber type. Recently, a novel splice variant of PGC-1α(NT-PGC-1α, amino acids 1–270) was cloned and found to be expressed in muscle. Here we use Flag-tagged NT-PGC-1αto examine the subcellular localization and regulation of NT-PGC-1αin skeletal muscle fibers. Flag-NT-PGC-1αis located predominantly in the myoplasm. Nuclear NT-PGC-1αcan be increased by activation of protein kinase A. Activation of p38 MAPK by muscle activity or of AMPK had no effect on the subcellular distribution of NT-PGC-1α. Inhibition of CRM1-mediated export only caused relatively slow nuclear accumulation of NT-PGC-1α, indicating that nuclear export of NT-PGC-1αmay be mediated by both CRM1-dependent and -independent pathways. Together these results suggest that the regulation of NT-PGC-1αin muscle fibers may be very different from that of the full-length PGC-1α, which is exclusively nuclear.

scholarly journals Myofibrillar regulatory mechanisms of stretch activation in mammalian striated muscle

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.

scholarly journals Comparison of the effects of inorganic phosphate on caffeine-induced Ca2+ release in fast- and slow-twitch mammalian skeletal muscle

2008 ◽  
Vol 294 (1) ◽  
pp. C97-C105 ◽  
Author(s):  
Giuseppe S. Posterino ◽  
Stacey L. Dunn
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Inorganic Phosphate ◽  
Fiber Type ◽  
Muscle Fibers ◽  
Creatine Phosphate ◽  
Mammalian Skeletal Muscle ◽  
Time Integral ◽  
Slow Twitch ◽  
Fast Twitch

We compared the effects of 50 mM Pi on caffeine-induced Ca2+ release in mechanically skinned fast-twitch (FT) and slow-twitch (ST) skeletal muscle fibers of the rat. The time integral (area) of the caffeine response was reduced by ∼57% (FT) and ∼27% (ST) after 30 s of exposure to 50 mM Pi in either the presence or absence of creatine phosphate (to buffer ADP). Differences in the sarcoplasmic reticulum (SR) Ca2+ content between FT and ST fibers [∼40% vs. 100% SR Ca2+ content (pCa 6.7), respectively] did not contribute to the different effects of Pi observed; underloading the SR of ST fibers so that the SR Ca2+ content approximated that of FT fibers resulted in an even smaller (∼21%), but not significant, reduction in caffeine-induced Ca2+ release by Pi. These observed differences between FT and ST fibers could arise from fiber-type differences in the ability of the SR to accumulate Ca2+-Pi precipitate. To test this, fibers were Ca2+ loaded in the presence of 50 mM Pi. In FT fibers, the maximum SR Ca2+ content (pCa 6.7) was subsequently increased by up to 13 times of that achieved when loading for 2 min in the absence of Pi. In ST fibers, the SR Ca2+ content was only doubled. These data show that Ca2+ release in ST fibers was less affected by Pi than FT fibers, and this may be due to a reduced capacity of ST SR to accumulate Ca2+-Pi precipitate. This may account, in part, for the fatigue-resistant nature of ST fibers.

scholarly journals Six1 and Eya1 Expression Can Reprogram Adult Muscle from the Slow-Twitch Phenotype into the Fast-Twitch Phenotype

2004 ◽  
Vol 24 (14) ◽  
pp. 6253-6267 ◽  
Author(s):  
Raphaelle Grifone ◽  
Christine Laclef ◽  
François Spitz ◽  
Soledad Lopez ◽  
Josiane Demignon ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Fiber Type ◽  
Muscle Fibers ◽  
Slow Twitch Muscle ◽  
Slow Twitch ◽  
Metabolic Properties ◽  
Transcriptional Complex ◽  
High Level ◽  
Fast Twitch ◽  
Aldolase A

ABSTRACT Muscle fibers show great differences in their contractile and metabolic properties. This diversity enables skeletal muscles to fulfill and adapt to different tasks. In this report, we show that the Six/Eya pathway is implicated in the establishment and maintenance of the fast-twitch skeletal muscle phenotype. We demonstrate that the MEF3/Six DNA binding element present in the aldolase A pM promoter mediates the high level of activation of this promoter in fast-twitch glycolytic (but not in slow-twitch) muscle fibers. We also show that among the Six and Eya gene products expressed in mouse skeletal muscle, Six1 and Eya1 proteins accumulate preferentially in the nuclei of fast-twitch muscles. The forced expression of Six1 and Eya1 together in the slow-twitch soleus muscle induced a fiber-type transition characterized by the replacement of myosin heavy chain I and IIA isoforms by the faster IIB and/or IIX isoforms, the activation of fast-twitch fiber-specific genes, and a switch toward glycolytic metabolism. Collectively, these data identify Six1 and Eya1 as the first transcriptional complex that is able to reprogram adult slow-twitch oxidative fibers toward a fast-twitch glycolytic phenotype.

The “KIMWIPE” Effect in Ultra-Thin Cryosections

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).

The Adaptive Potential of Skeletal Muscle Fibers

2002 ◽  
Vol 27 (4) ◽  
pp. 423-448 ◽  
Author(s):  
Dirk Pette
Keyword(s):  
Skeletal Muscle ◽  
Fiber Type ◽  
Muscle Fibers ◽  
Protein Isoforms ◽  
Mammalian Skeletal Muscle ◽  
Adaptive Potential ◽  
Hybrid Fibers ◽  
Neuromuscular Activity ◽  
Skeletal Muscle Fibers ◽  
Initial Location

Mammalian skeletal muscle fibers display a great adaptive potential. This potential results from the ability of muscle fibers to adjust their molecular, functional, and metabolic properties in response to altered functional demands, such as changes in neuromuscular activity or mechanical loading. Adaptive changes in the expression of myofibrillar and other protein isoforms result in fiber type transitions. These transitions occur in a sequential order and encompass a spectrum of pure and hybrid fibers. Depending on the quality, intensity, and duration of the alterations in functional demand, muscle fibers may undergo functional transitions in the direction of slow or fast, as well as metabolic transitions in the direction of aerobic-oxidative or glycotytic. The maximum range of possible transitions in either direction depends on the fiber phenotype and is determined by its initial location in the fiber spectrum. Key words: Ca-sequestering proteins, energy metabolism, fiber type transition, myofibrillar protein isofonns, myosin, neuromuscular activity

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