pH dependence of myosin binding-induced activation of the thin filament in cardiac myocytes and skeletal fibers

1996 ◽  
Vol 270 (3) ◽  
pp. H1008-H1014 ◽  
Author(s):  
J. M. Metzger
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Myocytes ◽  
Thin Filament ◽  
Ph Dependence ◽  
Muscle Fibers ◽  
Isometric Tension ◽  
Experimental Conditions ◽  
Skeletal Muscle Fibers ◽  
Myosin Binding ◽  
Fast Twitch

The pH dependence of myosin binding-induced thin filament activation was determined in permeabilized cardiac myocytes and slow- and fast-twitch single skeletal muscle fibers by experimental lowering of [MgATP] in the Ca(2+)-free solutions bathing the permeabilized preparations. As the pS (where S is [MgATP] and pS is -log[MgATP]) was increased from 3.0 to 8.0, isometric tension increased to a peak value in the pS range of 4.9-5.3. At pH 7.00, the transition from the relaxed to the activated rigor state was steep in cardiac myocytes [Hill value (nH) = 21.2 +/- 3.1 (SE)] and due to the apparent effect of strongly bound cross bridges to cooperatively activate the thin filament in the absence of added Ca2+. At pH 6.20, the steepness of the tension-pS relationship was markedly reduced (nH = 6.1 +/- 1.0) and the midpoint of the relationship (pS50) was shifted to higher pS values in cardiac myocytes. In comparison, reduced pH had no effect on the steepness or position of the tension-pS relationship in single slow- or fast-twitch skeletal muscle fibers. These findings suggest that myosin binding-induced activation of the thin filament is pH dependent in cardiac myocytes but not in skeletal muscle fibers under these experimental conditions in which Ca2+ is absent.

Effects on Ca(2+)-activated tension due to a synthetic NH2-terminal actin peptide in single skeletal muscle fibers

1995 ◽  
Vol 269 (5) ◽  
pp. C1193-C1199
Author(s):  
J. M. Metzger
Keyword(s):  
Skeletal Muscle ◽  
Thin Filament ◽  
Troponin I ◽  
Muscle Fibers ◽  
Isometric Tension ◽  
Specific Sequence ◽  
Tension Development ◽  
Terminal Domain ◽  
Skeletal Muscle Fibers ◽  
Inhibitory Region

Insight into the mechanism of force development in striated muscle will be provided by elucidating the specific regions of the actin molecule that interact with myosin and regulatory subunits of the thin filament during Ca(2+)-activated contraction. There is growing evidence that the acidic NH2-terminal domain of actin 1) may represent an important binding site for myosin and 2) may interact with the inhibitory region of troponin I. The purpose of this study was to determine the effects of a synthetic peptide corresponding to a specific sequence of the NH2-terminal domain of skeletal muscle actin on Ca(2+)-activated tension in chemically skinned single psoas skeletal muscle fibers. This study focused on the highly conserved Lys18-Arg28 amino acid sequence of actin, a region of native actin that is believed to interact with troponin I and myosin. The effects of synthetic actin peptide Lys18-Arg28 on tension development varied, depending on 1) the concentration of Ca2+ in the activating solutions and 2) the peptide concentration. At submaximal concentrations of Ca2+, isometric tension was reversibly potentiated in the presence of 100-500 microM synthetic actin peptide Lys18-Arg28. Importantly, scrambling the sequence of Lys18-Arg28 fully abolished the increase in Ca2+ sensitivity, providing evidence that the observed effects were specific to the sequence of peptide Lys18-Arg28. In contrast, maximum Ca(2+)-activated tension was inhibited by millimolar concentrations of Lys18-Arg28 and the scrambled peptide, indicating that this effect was nonspecific. The effect of peptide Lys18-Arg28 to increase the Ca2+ sensitivity of tension is not known but may be due to an effect of the actin peptide to alter thin filament activation, a possibility consistent with proposed interactions between this domain of actin and the inhibitory region of troponin I.

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 Effect of electromagnetic field GSM on contractile responses of fast‐twitch intact skeletal muscle fibers

2011 ◽  
Vol 25 (S1) ◽  
Author(s):  
Wiam Ramadan ◽  
Hanane Akhdar ◽  
Fatima Jebai ◽  
Yolla Makhour ◽  
Dana Zeyneddine ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Electromagnetic Field ◽  
Muscle Fibers ◽  
Contractile Responses ◽  
Skeletal Muscle Fibers ◽  
Fast Twitch

scholarly journals Exercise: Teaching myocytes new tricks

2017 ◽  
Vol 123 (2) ◽  
pp. 460-472 ◽  
Author(s):  
Scott K. Powers
Keyword(s):  
Skeletal Muscle ◽  
Exercise Training ◽  
Cardiac Myocytes ◽  
Endurance Exercise ◽  
Ischemia Reperfusion ◽  
Muscle Fibers ◽  
Cardiac Phenotype ◽  
Endurance Exercise Training ◽  
Skeletal Muscle Fibers ◽  
Exercise Induced

Endurance exercise training promotes numerous cellular adaptations in both cardiac myocytes and skeletal muscle fibers. For example, exercise training fosters changes in mitochondrial function due to increased mitochondrial protein expression and accelerated mitochondrial turnover. Additionally, endurance exercise training alters the abundance of numerous cytosolic and mitochondrial proteins in both cardiac and skeletal muscle myocytes, resulting in a protective phenotype in the active fibers; this exercise-induced protection of cardiac and skeletal muscle fibers is often referred to as “exercise preconditioning.” As few as 3–5 consecutive days of endurance exercise training result in a preconditioned cardiac phenotype that is sheltered against ischemia-reperfusion-induced injury. Similarly, endurance exercise training results in preconditioned skeletal muscle fibers that are resistant to a variety of stresses (e.g., heat stress, exercise-induced oxidative stress, and inactivity-induced atrophy). Many studies have probed the mechanisms responsible for exercise-induced preconditioning of cardiac and skeletal muscle fibers; these studies are important, because they provide an improved understanding of the biochemical mechanisms responsible for exercise-induced preconditioning, which has the potential to lead to innovative pharmacological therapies aimed at minimizing stress-induced injury to cardiac and skeletal muscle. This review summarizes the development of exercise-induced protection of cardiac myocytes and skeletal muscle fibers and highlights the putative mechanisms responsible for exercise-induced protection in the heart and skeletal muscles.

beta-Adrenergic modulation of Ba2+ currents and K+ contractures in frog slow skeletal muscle fibers

1997 ◽  
Vol 272 (1) ◽  
pp. C77-C81 ◽  
Author(s):  
M. Huerta ◽  
X. Trujillo ◽  
C. Vasquez
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Isometric Tension ◽  
External Application ◽  
Beta Adrenergic ◽  
Cyclic Monophosphate ◽  
Slow Skeletal Muscle ◽  
Skeletal Muscle Fibers ◽  
Adrenergic Modulation ◽  
Ca2 Channels

beta-Adrenergic modulation of the Ba2+ current (IBa) and K+ contracture in slow skeletal muscle fibers of the frog (Rana pipiens) were investigated in intact fibers with the three-microelectrode voltage-clamp technique and isometric tension measurements. Application of epinephrine (10(-6) to 10(-5) M) to the bath increased the amplitude of IBa. This increase was blocked by the beta-antagonist propranolol (3 microM), and a similar increase was observed with the beta-specific agonist isoproterenol (1 microM). Thus the epinephrine effect was mediated mainly by beta-adrenergic receptors. External application of permeable 8-bromoadenosine 3',5'-cyclic monophosphate (0.5 mM) increased the amplitude of both IBa and K+ contractures. The present results suggest that beta-adrenergic modulation of IBa in slow skeletal muscle fibers could reflect a modulation of Ca2+ channels via adenosine 3',5'-cyclic monophosphate (cAMP). cAMP (0.5 mM) also potentiated the K(+)-evoked tension in these slow fibers. The physiological contribution made by the modulation of slow skeletal muscle Ca2+ channels to the increase in tension is still not completely understood.

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.

scholarly journals Steady State Relation between Cytoplasmic Free Ca2+ Concentration and Force in Intact Frog Skeletal Muscle Fibers

1998 ◽  
Vol 111 (4) ◽  
pp. 505-519 ◽  
Author(s):  
Masato Konishi ◽  
Masaru Watanabe
Keyword(s):  
Skeletal Muscle ◽  
Steady State ◽  
Isometric Force ◽  
Muscle Fibers ◽  
Skinned Fibers ◽  
Hill Coefficient ◽  
Experimental Conditions ◽  
Skeletal Muscle Fibers ◽  
Force Relation ◽  
Series Of Experiments

The steady state relation between cytoplasmic Ca2+ concentration ([Ca2+]i) and force was studied in intact skeletal muscle fibers of frogs. Intact twitch fibers were injected with the dextran-conjugated Ca2+ indicator, fura dextran, and the fluorescence signals of fura dextran were converted to [Ca2+]i using calibration parameters previously estimated in permeabilized muscle fibers (Konishi and Watanabe. 1995. J. Gen. Physiol. 106:1123–1150). In the first series of experiments, [Ca2+]i and isometric force were simultaneously measured during high K+ depolarization. Slow changes in [Ca2+]i and force induced by 15–30 mM K+ appeared to be in equilibrium, as instantaneous [Ca2+]i versus force plot tracked the common path in the rising and relaxation phases of K+ contractures. In the second series of experiments, 2,5-di-tert-butylhydroquinone (TBQ), an inhibitor of the sarcoplasmic reticulum Ca2+ pump, was used to decrease the rate of decline of [Ca2+]i after tetanic stimulation. The decay time courses of both [Ca2+]i and force were dose-dependently slowed by TBQ up to 5 μM; the instantaneous [Ca2+]i– force relations were nearly identical at ≥1 μM TBQ, suggesting that the change in [Ca2+]i was slow enough to reach equilibrium with force. The [Ca2+]i–force data obtained from the two types of experiments were consistent with the Hill curve using a Hill coefficient of 3.2–3.9 and [Ca2+]i for half activation (Ca50) of 1.5–1.7 μM. However, if fura dextran reacts with Ca2+ with a 2.5-fold greater Kd as previously estimated from the kinetic fitting (Konishi and Watanabe. 1995. J. Gen. Physiol. 106:1123–1150), Ca50 would be 3.7–4.2 μM. We also studied the [Ca2+]–force relation in skinned fibers under similar experimental conditions. The average Hill coefficient and Ca50 were estimated to be 3.3 and 1.8 μM, respectively. Although uncertainties remain about the precise levels of [Ca2+]i, we conclude that the steady state force is a 3rd to 4th power function of [Ca2+]i, and Ca50 is in the low micromolar range in intact frog muscle fibers, which is in reasonable agreement with results obtained from skinned fibers.

Thalidomide attenuates tumor growth and preserves fast-twitch skeletal muscle fibers in cholangiocarcinoma rats

Surgery ◽  
2008 ◽  
Vol 143 (3) ◽  
pp. 375-383 ◽  
Author(s):  
Keng-Hao Liu ◽  
Li-Min Liao ◽  
Long-Sun Ro ◽  
Yu-Lien Wu ◽  
Ta-Sen Yeh
Keyword(s):  
Skeletal Muscle ◽  
Tumor Growth ◽  
Muscle Fibers ◽  
Skeletal Muscle Fibers ◽  
Fast Twitch

scholarly journals Alterations in Ca2+ sensitive tension due to partial extraction of C-protein from rat skinned cardiac myocytes and rabbit skeletal muscle fibers.

1991 ◽  
Vol 97 (6) ◽  
pp. 1141-1163 ◽  
Author(s):  
P A Hofmann ◽  
H C Hartzell ◽  
R L Moss
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Myocytes ◽  
Protein Extraction ◽  
Muscle Fibers ◽  
Extraction Procedure ◽  
Psoas Muscle ◽  
Similar Amount ◽  
C Protein ◽  
Skeletal Muscle Fibers ◽  
Partial Extraction

C-protein, a substantial component of muscle thick filaments, has been postulated to have various functions, based mainly on results from biochemical studies. In the present study, effects on Ca(2+)-activated tension due to partial removal of C-protein were investigated in skinned single myocytes from rat ventricle and rabbit psoas muscle. Isometric tension was measured at pCa values of 7.0 to 4.5: (a) in untreated myocytes, (b) in the same myocytes after partial extraction of C-protein, and (c) in some myocytes, after readdition of C-protein. The solution for extracting C-protein contained 10 mM EDTA, 31 mM Na2HPO2, 124 mM NaH2PO4, pH 5.9 (Offer et al., 1973; Hartzell and Glass, 1984). In addition, the extracting solution contained 0.2 mg/ml troponin and, for skeletal muscle, 0.2 mg/ml myosin light chain-2 in order to minimize loss of these proteins during the extraction procedure. Between 60 and 70% of endogenous C-protein was extracted from cardiac myocytes by a 1-h soak in extracting solution at 20-23 degrees C; a similar amount was extracted from psoas fibers during a 3-h soak at 25 degrees C. For both cardiac myocytes and skeletal muscle fibers, partial extraction of C-protein resulted in increased active tension at submaximal concentrations of Ca2+, but had little effect upon maximum tension. C-protein extraction also reduced the slope of the tension-pCa relationships, suggesting that the cooperativity of Ca2+ activation of tension was decreased. Readdition of C-protein to previously extracted myocytes resulted in recovery of both tension and slope to near their control values. The effects on tension did not appear to be due to disruption of cooperative activation of the thin filament, since C-protein extraction from cardiac myocytes that were 40-60% troponin-C (TnC) deficient produced effects similar to those observed in cells that were TnC replete. Measurements of the tension-pCa relationship in skeletal muscle fibers were also made at a sarcomere length of 3.5 microns which, because of the distribution of C-protein on the thick filament, should eliminate any interaction between C-protein and actin. The effects of C-protein extraction were similar at long and short sarcomere lengths. These data are consistent with a model in which C-protein modulates the range of movement of myosin, such that the probability of myosin binding to actin is increased after its extraction.

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