Mammalian skeletal muscle does not express functional voltage-gated H+ channels

High metabolic activity and existence of a large transmembrane inward electrochemical gradient for H+ at rest promote intracellular acidification of skeletal muscle. Exchangers and cotransports efficiently contend against accumulation of intracellular H+ and associated deleterious effects on muscle functions. Voltage-gated H+ channels have also been found to represent another H+ extrusion pathway in cultured muscle cells. Up to now, the skeletal muscle cell was therefore the unique vertebrate excitable cell in which voltage-gated H+ currents have been described. In this study, we show that, unlike cultured cells, single mouse muscle fibers do not generate H+ currents in response to depolarization. In contrast, expression of human voltage-gated H+ channels in mouse muscle gives rise to robust outward voltage-gated H+ currents. This result excludes that inappropriate experimental conditions may have failed to reveal voltage-gated H+ currents in control muscle. This work therefore demonstrates that fully differentiated mammalian muscle fibers do not express functional voltage-gated H+ channels and consequently can no longer be considered as the only vertebrate excitable cells exhibiting voltage-gated H+ currents.

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Mammalian muscle fibers may be simple as well as slow

The Journal of General Physiology ◽

10.1085/jgp.201912478 ◽

2019 ◽

Vol 151 (12) ◽

pp. 1334-1338 ◽

Cited By ~ 1

Author(s):

John M. Squire ◽

Pradeep K. Luther

Keyword(s):

Skeletal Muscle ◽

Lattice Structure ◽

Muscle Fibers ◽

Mammalian Skeletal Muscle ◽

Mammalian Muscle ◽

Simple Lattice ◽

New Evidence

Squire and Luther consider new evidence for a simple lattice structure in mammalian skeletal muscle.

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The Adaptive Potential of Skeletal Muscle Fibers

Canadian Journal of Applied Physiology ◽

10.1139/h02-023 ◽

2002 ◽

Vol 27 (4) ◽

pp. 423-448 ◽

Cited By ~ 109

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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Interdomain Interactions within Ryanodine Receptors Regulate Ca2+ Spark Frequency in Skeletal Muscle

The Journal of General Physiology ◽

10.1085/jgp.119.1.15 ◽

2001 ◽

Vol 119 (1) ◽

pp. 15-32 ◽

Cited By ~ 40

Author(s):

Alexander Shtifman ◽

Christopher W. Ward ◽

Takeshi Yamamoto ◽

Jianli Wang ◽

Beth Olbinski ◽

...

Keyword(s):

Skeletal Muscle ◽

Lipid Bilayers ◽

Laser Scanning ◽

Muscle Fibers ◽

Mammalian Skeletal Muscle ◽

Open Probability ◽

Release Channel ◽

Pronounced Increase ◽

Open Time ◽

Interdomain Interactions

DP4 is a 36-residue synthetic peptide that corresponds to the Leu2442-Pro2477 region of RyR1 that contains the reported malignant hyperthermia (MH) mutation site. It has been proposed that DP4 disrupts the normal interdomain interactions that stabilize the closed state of the Ca2+ release channel (Yamamoto, T., R. El-Hayek, and N. Ikemoto. 2000. J. Biol. Chem. 275:11618–11625). We have investigated the effects of DP4 on local SR Ca2+ release events (Ca2+ sparks) in saponin-permeabilized frog skeletal muscle fibers using laser scanning confocal microscopy (line-scan mode, 2 ms/line), as well as the effects of DP4 on frog SR vesicles and frog single RyR Ca2+ release channels reconstituted in planar lipid bilayers. DP4 caused a significant increase in Ca2+ spark frequency in muscle fibers. However, the mean values of the amplitude, rise time, spatial half width, and temporal half duration of the Ca2+ sparks, as well as the distribution of these parameters, remained essentially unchanged in the presence of DP4. Thus, DP4 increased the opening rate, but not the open time of the RyR Ca2+ release channel(s) generating the sparks. DP4 also increased [3H]ryanodine binding to SR vesicles isolated from frog and mammalian skeletal muscle, and increased the open probability of frog RyR Ca2+ release channels reconstituted in bilayers, without changing the amplitude of the current through those channels. However, unlike in Ca2+ spark experiments, DP4 produced a pronounced increase in the open time of channels in bilayers. The same peptide with an Arg17 to Cys17 replacement (DP4mut), which corresponds to the Arg2458-to-Cys2458 mutation in MH, did not produce a significant effect on RyR activation in muscle fibers, bilayers, or SR vesicles. Mg2+ dependence experiments conducted with permeabilized muscle fibers indicate that DP4 preferentially binds to partially Mg2+-free RyR(s), thus promoting channel opening and production of Ca2+ sparks.

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Immunolocalization of Sarcoplasmic Reticulum Proteins in Mammalian Skeletal Muscle Fibers

American Zoologist ◽

10.1093/icb/27.4.1021 ◽

1987 ◽

Vol 27 (4) ◽

pp. 1021-1032 ◽

Cited By ~ 3

Author(s):

ANNELISE O. JORGENSEN

Keyword(s):

Skeletal Muscle ◽

Sarcoplasmic Reticulum ◽

Muscle Fibers ◽

Mammalian Skeletal Muscle ◽

Skeletal Muscle Fibers

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Calcium Sparklets in Intact Mammalian Skeletal Muscle Fibers Expressing the Embryonic CaV1.1 Splice Variant

Biophysical Journal ◽

10.1016/j.bpj.2014.11.2759 ◽

2015 ◽

Vol 108 (2) ◽

pp. 504a

Author(s):

Beatrix Dienes ◽

Nasreen Sultana ◽

Janos Vincze ◽

Monika Sztretye ◽

Peter Szentesi ◽

...

Keyword(s):

Skeletal Muscle ◽

Splice Variant ◽

Muscle Fibers ◽

Mammalian Skeletal Muscle ◽

Skeletal Muscle Fibers

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

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1996.270.3.h1008 ◽

1996 ◽

Vol 270 (3) ◽

pp. H1008-H1014 ◽

Cited By ~ 1

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.

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Factors affecting SOCE activation in mammalian skeletal muscle fibers

The Journal of Physiological Sciences ◽

10.1007/s12576-009-0039-5 ◽

2009 ◽

Vol 59 (4) ◽

pp. 317-328 ◽

Cited By ~ 7

Author(s):

Pura Bolaños ◽

Alis Guillén ◽

Reinaldo DiPolo ◽

Carlo Caputo

Keyword(s):

Skeletal Muscle ◽

Muscle Fibers ◽

Mammalian Skeletal Muscle ◽

Factors Affecting ◽

Skeletal Muscle Fibers

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

The Journal of General Physiology ◽

10.1085/jgp.111.4.505 ◽

1998 ◽

Vol 111 (4) ◽

pp. 505-519 ◽

Cited By ~ 11

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.

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Single-fiber isolation and maintenance of satellite cell quiescence

Biochemistry and Cell Biology ◽

10.1139/o05-046 ◽

2005 ◽

Vol 83 (5) ◽

pp. 674-676 ◽

Cited By ~ 24

Author(s):

Ashley C Wozniak ◽

Judy E Anderson

Keyword(s):

Skeletal Muscle ◽

Satellite Cell ◽

Satellite Cells ◽

Muscle Fibers ◽

Single Fiber ◽

Skeletal Muscle Regeneration ◽

Mouse Muscle ◽

Collagenase Digestion ◽

Cell Quiescence ◽

Gentle Agitation

The activity of satellite cells during myogenesis, development, or skeletal muscle regeneration is strongly modelled using cultures of single muscle fibers. However, there are variations in reported features of gene or protein expression as examined with single-fiber cultures. Here, we examined the potential differences in activation of satellite cells on normal mouse muscle fibers produced during a standard isolation protocol, with or without agitation during collagenase digestion. Activation was detected in satellite cells on fibers after 24 and 48 h of culture in basal growth medium using immunodetection of the incorporation of bromodeoxyuridine (BrdU) into DNA and quantification of the number of BrdU-positive cells per fiber. After 24 and 48 h in culture under nonactivating conditions, the number of activated (BrdU+) satellite cells was greater on fibers that had received gentle agitation during collagenase digestion than on those that were subject to digestion without agitation during isolation. The findings are interpreted to mean that at least some of the variation among published reports may derive from the application of various methods of fiber isolation. The information should be useful for maintaining satellite cell quiescence during studies of the regulatory steps that lead to satellite cell activation.Key words: activation, skeletal muscle, proliferation, single-fiber culture, myogenesis.

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