scholarly journals Recordings of action potentials, charge movements, and sarcoplasmic reticulum Ca2+ release in isolated adult zebrafish fast skeletal muscle fibers reveals very fast kinetics of excitation–contraction coupling

2021 ◽  
Vol 154 (9) ◽  
Author(s):  
Romane Idoux ◽  
Christine Berthier ◽  
Vincent Jacquemond ◽  
Bruno Allard
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Action Potentials ◽  
Muscle Fibers ◽  
Fast Skeletal Muscle ◽  
Fast Kinetics ◽  
Ec Coupling ◽  
Skeletal Muscle Fibers ◽  
Charge Movements ◽  
Kinetics Of

The zebrafish has emerged as a very relevant animal model to decipher the pathophysiology of human muscle disorders. However, the vast majority of studies on zebrafish skeletal muscle have investigated genetic, histological, and molecular aspects, but functional approaches at the cellular level, especially in the field of excitation–contraction (EC) coupling, are scarcer and generally limited to cultured myotubes or fibers from embryonic zebrafish. Considering that zebrafish undergoes profound metamorphosis during transition from larval to adult stage and that number of muscle pathologies come up at ages far beyond embryonic stages, there is an actual need to investigate EC coupling in fully differentiated zebrafish skeletal muscle. In the present study, we were able to implement current and voltage clamp combined with intracellular Ca2+ measurements using the intracellularly loaded Ca2+ dye indo-1 in enzymatically isolated fast skeletal muscle fibers from 1-yr old zebrafish. Recording of action potentials (AP) in current-clamp conditions revealed very fast kinetics of the repolarization phase of AP. Measurements of intramembrane charge movements in voltage-clamp conditions showed that charge movement density was half that measured in mammalian fibers, but they displayed much faster kinetics. Ca2+ transients elicited by depolarization displayed a voltage-dependent phase of activation and voltage- and time-dependent phase of inactivation. Recording of Ca2+ signals elicited by trains of AP at different rates in current-clamp conditions indicated that Ca2+ signals fused at very high stimulation frequencies with no sign of Ca2+ signal decay for the entire 0.5 s duration of the stimulation, giving evidence that fibers were still able to generate AP and the sarcoplasmic reticulum to release Ca2+ with stimulation rates as high as 200 Hz. These data indicate that adult zebrafish fast skeletal muscle fibers exhibit strikingly fast kinetics of EC coupling from AP firing to charge movements and sarcoplasmic reticulum Ca2+ release.

scholarly journals Elevated nuclear Foxo1 suppresses excitability of skeletal muscle fibers

2013 ◽  
Vol 305 (6) ◽  
pp. C643-C653 ◽  
Author(s):  
Erick O. Hernández-Ochoa ◽  
Tova Neustadt Schachter ◽  
Martin F. Schneider
Keyword(s):  
Skeletal Muscle ◽  
Electrical Stimulation ◽  
Muscle Atrophy ◽  
Action Potentials ◽  
Muscle Fibers ◽  
Calcium Transients ◽  
Skeletal Muscle Atrophy ◽  
Nuclear Activity ◽  
Ec Coupling ◽  
Skeletal Muscle Fibers

Forkhead box O 1 (Foxo1) controls the expression of proteins that carry out processes leading to skeletal muscle atrophy, making Foxo1 of therapeutic interest in conditions of muscle wasting. The transcription of Foxo1-regulated proteins is dependent on the translocation of Foxo1 to the nucleus, which can be repressed by insulin-like growth factor-1 (IGF-1) treatment. The role of Foxo1 in muscle atrophy has been explored at length, but whether Foxo1 nuclear activity affects skeletal muscle excitation-contraction (EC) coupling has not yet been examined. Here, we use cultured adult mouse skeletal muscle fibers to investigate the effects of Foxo1 overexpression on EC coupling. Fibers expressing Foxo1-green fluorescent protein (GFP) exhibit an inability to contract, impaired propagation of action potentials, and ablation of calcium transients in response to electrical stimulation compared with fibers expressing GFP alone. Evaluation of the transverse (T)-tubule system morphology, the membranous system involved in the radial propagation of the action potential, revealed an intact T-tubule network in fibers overexpressing Foxo1-GFP. Interestingly, long-term IGF-1 treatment of Foxo1-GFP fibers, which maintains Foxo1-GFP outside the nucleus, prevented the loss of normal calcium transients, indicating that Foxo1 translocation and the atrogenes it regulates affect the expression of proteins involved in the generation and/or propagation of action potentials. A reduction in the sodium channel Nav1.4 expression in fibers overexpressing Foxo1-GFP was also observed in the absence of IGF-1. We conclude that increased nuclear activity of Foxo1 prevents the normal muscle responses to electrical stimulation and that this indicates a novel capability of Foxo1 to disable the functional activity of skeletal muscle.

Uptake and caffeine-induced release of calcium in fast muscle fibers of Xenopus laevis: effects of MgATP and P(i)

1993 ◽  
Vol 265 (3) ◽  
pp. C650-C657 ◽  
Author(s):  
G. J. Stienen ◽  
I. A. van Graas ◽  
G. Elzinga
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Xenopus Laevis ◽  
Muscle Fatigue ◽  
Muscle Fibers ◽  
Force Response ◽  
Fast Skeletal Muscle ◽  
Reduction In Force ◽  
Kinetics Of ◽  
Uptake And Release

To elucidate the origin of the reduction in force during prolonged muscle fatigue, the dependency of Ca2+ uptake and release on MgATP and P(i) concentration was studied in saponin-skinned fast skeletal muscle fibers of the iliofibularis muscle of Xenopus laevis at 3 degrees C. The sarcoplasmic reticulum was loaded with Ca2+ for 5 min at pCa 7.0. The amount of Ca2+ released was derived from the area of the caffeine-induced force response. Ca2+ uptake increased with the MgATP concentration present during loading. It was half maximal at 20 microM and saturated at higher concentrations. The kinetics of Ca2+ release were affected for MgATP concentrations between 0.1 and 0.5 mM or less, but the amount of Ca2+ released by caffeine in ATP-free solutions was substantial. Phosphate (15 mM) only slightly reduced Ca2+ uptake when the loading period was short (1 min). It is unlikely, therefore, that the reduction in MgATP concentration contributes to the depression of Ca2+ released from the sarcoplasmic reticulum during fatigue. The increase in P(i) concentration could play a small role by reducing Ca2+ uptake.

Evidence for Na+/Ca2+exchange in intact single skeletal muscle fibers from the mouse

1998 ◽  
Vol 274 (4) ◽  
pp. C940-C946 ◽  
Author(s):  
Christopher D. Balnave ◽  
David G. Allen
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Muscle Fibers ◽  
Exchange Mechanism ◽  
Initial Exposure ◽  
Mouse Skeletal Muscle ◽  
Reverse Mode ◽  
Skeletal Muscle Fibers ◽  
Plateau Level ◽  
Sustained Increase

The myoplasmic free Ca2+concentration ([Ca2+]i) was measured in intact single fibers from mouse skeletal muscle with the fluorescent Ca2+ indicator indo 1. Some fibers were perfused in a solution in which the concentration of Na+ was reduced from 145.4 to 0.4 mM (low-Na+solution) in an attempt to activate reverse-mode Na+/Ca2+exchange (Ca2+ entry in exchange for Na+ leaving the cell). Under normal resting conditions, application of low-Na+ solution only increased [Ca2+]iby 5.8 ± 1.8 nM from a mean resting [Ca2+]iof 42 nM. In other fibers, [Ca2+]iwas elevated by stimulating sarcoplasmic reticulum (SR) Ca2+ release with caffeine (10 mM) and by inhibiting SR Ca2+ uptake with 2,5-di( tert-butyl)-1,4-benzohydroquinone (TBQ; 0.5 μM) in an attempt to activate forward-mode Na+/Ca2+exchange (Ca2+ removal from the cell in exchange for Na+ influx). These two agents caused a large increase in [Ca2+]i, which then declined to a plateau level approximately twice the baseline [Ca2+]iover 20 min. If the cell was allowed to recover between exposures to caffeine and TBQ in a solution in which Ca2+ had been removed, the increase in [Ca2+]iduring the second exposure was very low, suggesting that Ca2+ had left the cell during the initial exposure. Application of caffeine and TBQ to a preparation in low-Na+ solution produced a large, sustained increase in [Ca2+]iof ∼1 μM. However, when cells were exposed to caffeine and TBQ in a low-Na+ solution in which Ca2+ had been removed, a sustained increase in [Ca2+]iwas not observed, although [Ca2+]iremained higher and declined slower than in normal Na+ solution. This suggests that forward-mode Na+/Ca2+exchange contributed to the fall of [Ca2+]iin normal Na+ solution, but when extracellular Na+ was low, a prolonged elevation of [Ca2+]icould activate reverse-mode Na+/Ca2+exchange. The results provide evidence that skeletal muscle fibers possess a Na+/Ca2+exchange mechanism that becomes active in its forward mode when [Ca2+]iis increased to levels similar to that obtained during contraction.

Determinants of relaxation rate in skinned frog skeletal muscle fibers

1998 ◽  
Vol 274 (6) ◽  
pp. C1608-C1615 ◽  
Author(s):  
Philip A. Wahr ◽  
J. David Johnson ◽  
Jack. A. Rall
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Slow Phase ◽  
Frog Skeletal Muscle ◽  
Force Of Contraction ◽  
Thin Filaments ◽  
Fast Phase ◽  
Skeletal Muscle Fibers ◽  
Kinetics Of ◽  
Overall Kinetics

The influences of sarcomere uniformity and Ca2+ concentration on the kinetics of relaxation were examined in skinned frog skeletal muscle fibers induced to relax by rapid sequestration of Ca2+ by the photolysis of the Ca2+ chelator, diazo-2, at 10°C. Compared with an intact fiber, diazo-2-induced relaxation exhibited a faster and shorter initial slow phase and a fast phase with a longer tail. Stabilization of the sarcomeres by repeated releases and restretches during force development increased the duration of the slow phase and slowed its kinetics. When force of contraction was decreased by lowering the Ca2+concentration, the overall kinetics of relaxation was accelerated, with the slow phase being the most sensitive to Ca2+ concentration. Twitchlike contractions were induced by photorelease of Ca2+ from a caged Ca2+ (DM-Nitrophen), with subsequent Ca2+ sequestration by intact sarcoplasmic reticulum or Ca2+ rebinding to caged Ca2+. These twitchlike responses exhibited relaxation kinetics that were about twofold slower than those observed in intact fibers. Results suggest that the slow phase of relaxation is influenced by the degree of sarcomere homogeneity and rate of Ca2+ dissociation from thin filaments. The fast phase of relaxation is in part determined by the level of Ca2+ activation.

scholarly journals Effects of Cannabinoids on Caffeine Contractures in Slow and Fast Skeletal Muscle Fibers of the Frog

2009 ◽  
Vol 229 (2) ◽  
pp. 91-99 ◽  
Author(s):  
Miguel Huerta ◽  
Mónica Ortiz-Mesina ◽  
Xóchitl Trujillo ◽  
Enrique Sánchez-Pastor ◽  
Clemente Vásquez ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Fast Skeletal Muscle ◽  
Skeletal Muscle Fibers ◽  
Caffeine Contractures
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