Effects of Azumolene on Ca<sup>2+</sup>Sparks in Skeletal Muscle Fibers

Zhang, Yingfan; Rodney, George G.; Schneider, Martin F.

doi:10.1124/jpet.105.084046

Cited by 24 publications

(23 citation statements)

References 40 publications

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“…Azumolene, a Ca 2ϩ release modulator that suppresses the activity of the SR RyR Ca 2ϩ release channel (28), was used to address its effect on the activity of Ca 2ϩ sparks on day 7 dedifferentiated fibers. In fluo 4-loaded day 7 dedifferentiated fibers azumolene treatment (10 M for 10 min) completely suppressed Ca 2ϩ release events, indicating that RyR channel activity underlies increased Ca 2ϩ sparks (data not shown).…”

Section: Resultsmentioning

confidence: 99%

Ca²⁺ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Brown

Rodney²,

Hernández‐Ochoa³

et al. 2007

American Journal of Physiology-Cell Physiology

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Ca(+) sparks are rare in healthy adult mammalian skeletal muscle but may appear when adult fiber integrity is compromised, and occur in embryonic muscle but decline as the animal develops. Here we used cultured adult mouse flexor digitorum brevis muscle fibers to monitor occurrence of Ca(2+) sparks during maintenance of adult fiber morphology and during eventual fiber morphological dedifferentiation after various times in culture. Fibers cultured for up to 3 days retain normal morphology and striated appearance. Ca(2+) sparks were rare in these fibers. At 5-7 days in culture, many of the original muscle fibers exhibit sprouting and loss of striations, as well as the occurrence of spontaneous Ca(2+) sparks. The average rate of occurrence of Ca(2+) sparks is >10-fold higher after 5-7 days in culture than in days 1-3. With the use of fibers cultured for 7 days, application of the Ca(2+) channel blockers Co(2+) or nifedipine almost completely suppressed the occurrence of Ca(2+) sparks, as previously shown in embryonic fibers, suggesting that Ca(2+) sparks may be generated by similar mechanisms in dedifferentiating cultured adult fibers and in embryonic fibers before final differentiation. The sarcomeric disruption observed under transmitted light microscopy in dedifferentiating fibers was accompanied by morphological changes in the transverse (T) tubular system, as observed by fluorescence confocal imaging of both an extracellular marker dye and membrane staining dyes. Changes in T tubule morphology coincided with the appearance of Ca(2+) sparks, suggesting that Ca(2+) sparks may either be a signal for, or the result of, disruption of DHPR-ryanodine receptor 1 coupling.

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Section: Resultsmentioning

confidence: 99%

Ca²⁺ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Brown

Rodney²,

Hernández‐Ochoa³

et al. 2007

American Journal of Physiology-Cell Physiology

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“…Dantrolene was also found to inhibit DHPR Ca 2ϩ currents (4,43). In addition, azumolene (a dantrolene analog) decreased the frequency but not the shape (amplitude, duration, and width) of local events of RyR1-mediated Ca 2ϩ release (Ca 2ϩ sparks), indicating that the gating of RyR1 channels during the events was not affected by dantrolene derivatives (49). Similar decrease in Ca 2ϩ spark frequency is found with the DHPR antagonist nifedipine, which appears to stabilize physical interactions between DHPR and RyR1 (52).…”

Section: Discussionmentioning

confidence: 99%

Halothane modulation of skeletal muscle ryanodine receptors: dependence on Ca²⁺, Mg²⁺, and ATP

Diaz-Sylvester¹,

Porta²,

Copello³

2008

American Journal of Physiology-Cell Physiology

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Diaz-Sylvester PL, Porta M, Copello JA. Halothane modulation of skeletal muscle ryanodine receptors: dependence on Ca 2ϩ , Mg 2ϩ , and ATP. Am J Physiol Cell Physiol 294: C1103-C1112, 2008. First published February 27, 2008 doi:10.1152/ajpcell.90642.2007 susceptibility is a genetic disorder of skeletal muscle associated with mutations in the ryanodine receptor isoform 1 (RyR1) of sarcoplasmic reticulum (SR). In MH-susceptible skeletal fibers, RyR1-mediated Ca 2ϩ release is highly sensitive to activation by the volatile anesthetic halothane. Indeed, studies with isolated RyR1 channels (using simple Cs ϩ solutions) found that halothane selectively affects mutated but not wild-type RyR1 function. However, studies in skeletal fibers indicate that halothane can also activate wild-type RyR1-mediated Ca 2ϩ release. We hypothesized that endogenous RyR1 agonists (ATP, lumenal Ca 2ϩ ) may increase RyR1 sensitivity to halothane. Consequently, we studied how these agonists affect halothane action on rabbit skeletal RyR1 reconstituted into planar lipid bilayers. We found that cytosolic ATP is required for halothane-induced activation of the skeletal RyR1. Unlike RyR1, cardiac RyR2 (much less sensitive to ATP) responded to halothane even in the absence of this agonist. ATP-dependent halothane activation of RyR1 was enhanced by cytosolic Ca 2ϩ (channel agonist) and counteracted by Mg 2ϩ (channel inhibitor). Dantrolene, a muscle relaxant used to treat MH episodes, did not affect RyR1 or RyR2 basal activity and did not interfere with halothane-induced activation. Studies with skeletal SR microsomes confirmed that halothane-induced RyR1-mediated SR Ca 2ϩ release is enhanced by high ATP-low Mg 2ϩ in the cytosol and by increased SR Ca 2ϩ load. Thus, physiological or pathological processes that induce changes in cellular levels of these modulators could affect RyR1 sensitivity to halothane in skeletal fibers, including the outcome of halothane-induced contracture tests used to diagnose MH susceptibility.

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“…Dantrolene, and presumably its more water-soluble analogue azumolene, bind with high affinity to skeletal muscle SR membrane preparations, but not to sarcolemmal or t-tubule membranes [42,43]. A discrete dantrolene binding site within RyR1 (a.a. 590-609) was identified [43] and proposed to suppress RyR1 channel opening [44] by promoting RyR1 interdomain interactions that stabilize the closed state of the channel [45]. While dantrolene reduces electrically-evoked Ca 2+ release in myotubes [46], as well as both SR Ca 2+ release and [ 3 H]ryanodine binding to SR vesicles [47], two separate studies failed to observe a direct effect of dantrolene on purified RyR1 channel gating following incorporation in artificial planar lipid bilayers [46,48].…”

Section: Discussionmentioning

confidence: 99%

Accelerated Activation of SOCE Current in Myotubes from Two Mouse Models of Anesthetic- and Heat-Induced Sudden Death

2013

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Store-operated calcium entry (SOCE) channels play an important role in Ca2+ signaling. Recently, excessive SOCE was proposed to play a central role in the pathogenesis of malignant hyperthermia (MH), a pharmacogenic disorder of skeletal muscle. We tested this hypothesis by characterizing SOCE current (ISkCRAC) magnitude, voltage dependence, and rate of activation in myotubes derived from two mouse models of anesthetic- and heat-induced sudden death: 1) type 1 ryanodine receptor (RyR1) knock-in mice (Y524S/+) and 2) calsequestrin 1 and 2 double knock-out (dCasq-null) mice. ISkCRAC voltage dependence and magnitude at -80 mV were not significantly different in myotubes derived from wild type (WT), Y524S/+ and dCasq-null mice. However, the rate of ISkCRAC activation upon repetitive depolarization was significantly faster at room temperature in myotubes from Y524S/+ and dCasq-null mice. In addition, the maximum rate of ISkCRAC activation in dCasq-null myotubes was also faster than WT at more physiological temperatures (35-37°C). Azumolene (50 µM), a more water-soluble analog of dantrolene that is used to reverse MH crises, failed to alter ISkCRAC density or rate of activation. Together, these results indicate that while an increased rate of ISkCRAC activation is a common characteristic of myotubes derived from Y524S/+ and dCasq-null mice and that the protective effects of azumolene are not due to a direct inhibition of SOCE channels.

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Effects of Azumolene on Ca²⁺Sparks in Skeletal Muscle Fibers

Abstract: Azumolene is an analog of dantrolene, the only approved medicine for treatment of malignant hyperthermia (MH). The pharmacological mechanism of these drugs is to inhibit skeletal muscle sarcoplasmic reticulum (SR)

Cited by 24 publications

References 40 publications

Ca²⁺ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Ca²⁺ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Halothane modulation of skeletal muscle ryanodine receptors: dependence on Ca²⁺, Mg²⁺, and ATP

Accelerated Activation of SOCE Current in Myotubes from Two Mouse Models of Anesthetic- and Heat-Induced Sudden Death

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Effects of Azumolene on Ca2+Sparks in Skeletal Muscle Fibers

Abstract: Azumolene is an analog of dantrolene, the only approved medicine for treatment of malignant hyperthermia (MH). The pharmacological mechanism of these drugs is to inhibit skeletal muscle sarcoplasmic reticulum (SR)

Cited by 24 publications

References 40 publications

Ca2+ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Ca2+ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Halothane modulation of skeletal muscle ryanodine receptors: dependence on Ca2+, Mg2+, and ATP

Accelerated Activation of SOCE Current in Myotubes from Two Mouse Models of Anesthetic- and Heat-Induced Sudden Death

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Effects of Azumolene on Ca²⁺Sparks in Skeletal Muscle Fibers

Ca²⁺ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Ca²⁺ sparks and T tubule reorganization in dedifferentiating adult mouse skeletal muscle fibers

Halothane modulation of skeletal muscle ryanodine receptors: dependence on Ca²⁺, Mg²⁺, and ATP