Calcium phosphate precipitation in the sarcoplasmic reticulum reduces action potential-mediated Ca2+ release in mammalian skeletal muscle

During vigorous exercise, Pi concentration levels within the cytoplasm of fast-twitch muscle fibers may reach ≥30 mM. Cytoplasmic Pi may enter the sarcoplasmic reticulum (SR) and bind to Ca2+ to form a precipitate (CaPi), thus reducing the amount of releasable Ca2+. Using mechanically skinned rat fast-twitch muscle fibers, which retain the normal action potential-mediated Ca2+ release mechanism, we investigated the consequences of Pi exposure on normal excitation-contraction coupling. The total amount of Ca2+ released from the SR by a combined caffeine/low-Mg2+ concentration stimulus was reduced by ∼20%, and the initial rate of force development slowed after 2-min exposure to 30 mM Pi (with or without the presence creatine phosphate). Peak (50 Hz) tetanic force was also reduced (by ∼25% and ∼45% after 10 and 30 mM Pi exposure, respectively). Tetanic force responses produced after 30 mM Pi exposure were nearly identical to those observed in the same fiber after depletion of total SR Ca2+ by ∼35%. Ca2+ content assays revealed that the total amount of Ca2+ in the SR was not detectably changed by exposure to 30 mM Pi, indicating that Ca2+ had not leaked from the SR but instead formed a precipitate with the Pi, reducing the amount of available Ca2+ for rapid release. These results suggest that CaPi precipitation that occurs within the SR could contribute to the failure of Ca2+ release observed in the later stages of metabolic muscle fatigue. They also demonstrate that the total amount of Ca2+ stored in the SR cannot drop substantially below the normal endogenous level without reducing tetanic force responses.

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

AJP Cell Physiology ◽

10.1152/ajpcell.00155.2007 ◽

2008 ◽

Vol 294 (1) ◽

pp. C97-C105 ◽

Cited By ~ 7

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.

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Regulation of ClC-1 and KATP channels in action potential–firing fast-twitch muscle fibers

The Journal of General Physiology ◽

10.1085/jgp.200910290111709c ◽

2009 ◽

Vol 134 (6) ◽

pp. 523-523

Author(s):

Thomas Holm Pedersen ◽

Frank Vincenzo de Paoli ◽

John A. Flatman ◽

Ole Bækgaard Nielsen

Keyword(s):

Action Potential ◽

Muscle Fibers ◽

Katp Channels ◽

Action Potential Firing ◽

Potential Firing ◽

Fast Twitch Muscle ◽

Fast Twitch

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Transverse tubular system depolarization reduces tetanic force in rat skeletal muscle fibers by impairing action potential repriming

AJP Cell Physiology ◽

10.1152/ajpcell.00006.2007 ◽

2007 ◽

Vol 292 (6) ◽

pp. C2112-C2121 ◽

Cited By ~ 15

Author(s):

T. L. Dutka ◽

G. D. Lamb

Keyword(s):

Muscle Fibers ◽

Force Output ◽

Tetanic Force ◽

Internal Solution ◽

Transverse Tubular System ◽

Tubular System ◽

Fast Twitch Muscle ◽

Fast Twitch ◽

Pulse Stimulation ◽

T System

When muscle fibers are repeatedly stimulated, they may become depolarized and force output decline. Excitation of the transverse tubular system (T-system) is critical for activation, but its role in muscle fatigue is poorly understood. Here, mechanically skinned fibers from rat fast-twitch muscle were used, because the sarcolemma is absent but the T-system retains normal excitability and its properties can be studied in isolation. The T-system membrane was fully polarized by bathing the skinned fiber in an internal solution with 126 mM K+ (control solution) or set at partially depolarized levels (approximately −63 and −58 mV) in solutions with 66 or 55 mM K+, respectively, and action potentials (APs) were triggered in the sealed T-system by field stimulation. Prolonged depolarization of the T-system reduced tetanic force proportionately more than twitch force, with greater effect at higher stimulation frequency (responses at 20 and 100 Hz reduced to 71 and 62% in 66 mM K+ and to 54 and 35% in 55 mM K+, respectively). Double-pulse stimulation showed that depolarization increased the repriming period (estimated minimum time before a second AP can be produced) from ∼4 ms to ∼7.5 and 15 ms in the 66 and 55 mM K+ solutions, respectively. These results demonstrate that T-system depolarization reduces tetanic force by impairing AP repriming, rather than by preventing AP generation per se or by inactivating the T-system voltage sensors. The findings also explain why it is advantageous to reduce the rate of motoneuron stimulation to muscles during repeated or prolonged periods of activity.

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Regulation of ClC-1 and KATP channels in action potential–firing fast-twitch muscle fibers

The Journal of General Physiology ◽

10.1085/jgp.200910290 ◽

2009 ◽

Vol 134 (4) ◽

pp. 309-322 ◽

Cited By ~ 44

Author(s):

Thomas Holm Pedersen ◽

Frank Vincenzo de Paoli ◽

John A. Flatman ◽

Ole Bækgaard Nielsen

Keyword(s):

Action Potential ◽

Phase 1 ◽

Muscle Fibers ◽

Katp Channels ◽

Membrane Currents ◽

Resting Membrane Potential ◽

Phase 2 ◽

Channel Inhibition ◽

Fast Twitch Muscle ◽

Fast Twitch

Action potential (AP) excitation requires a transient dominance of depolarizing membrane currents over the repolarizing membrane currents that stabilize the resting membrane potential. Such stabilizing currents, in turn, depend on passive membrane conductance (Gm), which in skeletal muscle fibers covers membrane conductances for K+ (GK) and Cl− (GCl). Myotonic disorders and studies with metabolically poisoned muscle have revealed capacities of GK and GCl to inversely interfere with muscle excitability. However, whether regulation of GK and GCl occur in AP-firing muscle under normal physiological conditions is unknown. This study establishes a technique that allows the determination of GCl and GK with a temporal resolution of seconds in AP-firing muscle fibers. With this approach, we have identified and quantified a biphasic regulation of Gm in active fast-twitch extensor digitorum longus fibers of the rat. Thus, at the onset of AP firing, a reduction in GCl of ∼70% caused Gm to decline by ∼55% in a manner that is well described by a single exponential function characterized by a time constant of ∼200 APs (phase 1). When stimulation was continued beyond ∼1,800 APs, synchronized elevations in GK (∼14-fold) and GCl (∼3-fold) caused Gm to rise sigmoidally to ∼400% of its level before AP firing (phase 2). Phase 2 was often associated with a failure to excite APs. When AP firing was ceased during phase 2, Gm recovered to its level before AP firing in ∼1 min. Experiments with glibenclamide (KATP channel inhibitor) and 9-anthracene carboxylic acid (ClC-1 Cl− channel inhibitor) revealed that the decreased Gm during phase 1 reflected ClC-1 channel inhibition, whereas the massively elevated Gm during phase 2 reflected synchronized openings of ClC-1 and KATP channels. In conclusion, GCl and GK are acutely regulated in AP-firing fast-twitch muscle fibers. Such regulation may contribute to the physiological control of excitability in active muscle.

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Effects of fatigue on sarcoplasmic reticulum and myofibrillar properties of rat single muscle fibers

Journal of Applied Physiology ◽

10.1152/jappl.2000.89.3.891 ◽

2000 ◽

Vol 89 (3) ◽

pp. 891-898 ◽

Cited By ~ 17

Author(s):

D. Danieli-Betto ◽

E. Germinario ◽

A. Esposito ◽

D. Biral ◽

R. Betto

Keyword(s):

Sarcoplasmic Reticulum ◽

Muscle Fibers ◽

Normal Medium ◽

Regulatory Myosin Light Chain ◽

Fatigue Development ◽

Slow Twitch Muscle ◽

Fast Twitch Muscle ◽

Slow Twitch ◽

Fast Twitch

Force decline during fatigue in skeletal muscle is attributed mainly to progressive alterations of the intracellular milieu. Metabolite changes and the decline in free myoplasmic calcium influence the activation and contractile processes. This study was aimed at evaluating whether fatigue also causes persistent modifications of key myofibrillar and sarcoplasmic reticulum (SR) proteins that contribute to tension reduction. The presence of such modifications was investigated in chemically skinned fibers, a procedure that replaces the fatigued cytoplasm from the muscle fiber with a normal medium. Myofibrillar Ca2+ sensitivity was reduced in slow-twitch muscle (for example, the pCa value corresponding to 50% of maximum tension was 6.23 ± 0.03 vs. 5.99 + 0.05, P < 0.01, in rested and fatigued fibers) and not modified in fast-twitch muscle. Phosphorylation of the regulatory myosin light chain isoform increased in fast-twitch muscle. The rate of SR Ca2+ uptake was increased in slow-twitch muscle fibers (14.2 ± 1.0 vs. 19.6 ± 2.5 nmol · min−1 · mg fiber protein−1, P < 0.05) and not altered in fast-twitch fibers. No persistent modifications of SR Ca2+ release properties were found. These results indicate that persistent modifications of myofibrillar and SR properties contribute to fatigue-induced muscle force decline only in slow fibers. These alterations may be either enhanced or counteracted, in vivo, by the metabolic changes that normally occur during fatigue development.

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High-speed jaw-opening exercise in training suprahyoid fast-twitch muscle fibers

Clinical Interventions in Aging ◽

10.2147/cia.s152821 ◽

2018 ◽

Vol Volume 13 ◽

pp. 125-131 ◽

Cited By ~ 5

Author(s):

Mariko Matsubara ◽

Haruka Tohara ◽

Koji Hara ◽

Hiromichi Shinozaki ◽

Yasuhiro Yamazaki ◽

...

Keyword(s):

High Speed ◽

Muscle Fibers ◽

Jaw Opening ◽

Fast Twitch Muscle ◽

Fast Twitch

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lncRNA-Six1 Is a Target of miR-1611 that Functions as a ceRNA to Regulate Six1 Protein Expression and Fiber Type Switching in Chicken Myogenesis

Cells ◽

10.3390/cells7120243 ◽

2018 ◽

Vol 7 (12) ◽

pp. 243 ◽

Cited By ~ 10

Author(s):

Manting Ma ◽

Bolin Cai ◽

Liang Jiang ◽

Bahareldin Ali Abdalla ◽

Zhenhui Li ◽

...

Keyword(s):

Fiber Type ◽

Muscle Fibers ◽

Muscle Fiber Types ◽

Fiber Types ◽

Proliferation And Differentiation ◽

Slow Twitch Muscle ◽

Fast Twitch Muscle ◽

Slow Twitch ◽

Slow Twitch Fibers ◽

Fast Twitch

Emerging studies indicate important roles for non-coding RNAs (ncRNAs) as essential regulators in myogenesis, but relatively less is known about their function. In our previous study, we found that lncRNA-Six1 can regulate Six1 in cis to participate in myogenesis. Here, we studied a microRNA (miRNA) that is specifically expressed in chickens (miR-1611). Interestingly, miR-1611 was found to contain potential binding sites for both lncRNA-Six1 and Six1, and it can interact with lncRNA-Six1 to regulate Six1 expression. Overexpression of miR-1611 represses the proliferation and differentiation of myoblasts. Moreover, miR-1611 is highly expressed in slow-twitch fibers, and it drives the transformation of fast-twitch muscle fibers to slow-twitch muscle fibers. Together, these data demonstrate that miR-1611 can mediate the regulation of Six1 by lncRNA-Six1, thereby affecting proliferation and differentiation of myoblasts and transformation of muscle fiber types.

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Impaired sarcoplasmic reticulum Ca2+ release rate after fatiguing stimulation in rat skeletal muscle

Journal of Applied Physiology ◽

10.1152/jappl.2000.89.1.210 ◽

2000 ◽

Vol 89 (1) ◽

pp. 210-217 ◽

Cited By ~ 50

Author(s):

Niels Ørtenblad ◽

Gisela Sjøgaard ◽

Klavs Madsen

Keyword(s):

Sarcoplasmic Reticulum ◽

Release Rate ◽

Slow Phase ◽

Release Mechanism ◽

Rat Skeletal Muscle ◽

Slow Recovery ◽

Tetanic Force ◽

Longus Muscle ◽

Two Phases

The purpose of the study was to characterize the sarcoplasmic reticulum (SR) function and contractile properties before and during recovery from fatigue in the rat extensor digitorum longus muscle. Fatiguing contractions (60 Hz, 150 ms/s for 4 min) induced a reduction of the SR Ca2+release rate to 66% that persisted for 1 h, followed by a gradual recovery to 87% of prefatigue release rate at 3 h recovery. Tetanic force and rate of force development (+dF/d t) and relaxation (−dF/d t) were depressed by ∼80% after stimulation. Recovery occurred in two phases: an initial phase, in which during the first 0.5–1 h the metabolic state recovered to resting levels, and a slow phase from 1–3 h characterized by a rather slow recovery of the mechanical properties. The recovery of SR Ca2+ release rate was closely correlated to +dF/d t during the slow phase of recovery ( r 2 = 0.51; P < 0.05). Despite a slowing of the relaxation rate, we did not find any significant alterations in the SR Ca2+ uptake function. These data demonstrate that the Ca2+ release mechanism of SR is sensitive to repetitive in vitro muscle contraction. Moreover, the results indicate that +dF/d t to some extent depends on the rate of Ca2+ release during the slow phase of recovery.

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