scholarly journals The Changes in Ca2+ Sparks Associated with Measured Modifications of Intra-store Ca2+ Concentration in Skeletal Muscle

2006 ◽  
Vol 128 (1) ◽  
pp. 45-54 ◽  
Author(s):  
Bradley S. Launikonis ◽  
Jingsong Zhou ◽  
Demetrio Santiago ◽  
Gustavo Brum ◽  
Eduardo Ríos
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Muscle ◽  
Confocal Imaging ◽  
Frog Skeletal Muscle ◽  
Average Increase ◽  
Global Level ◽  
Event Frequency ◽  
Average Change ◽  
Contractile Activation

In cardiac muscle and amphibian skeletal muscle, the intracellular Ca2+ release that signals contractile activation proceeds by discrete local packets, which result in Ca2+ sparks. The remarkably stereotyped duration of these release events requires a robustly timed termination mechanism. In cardiac muscle the mechanism of spark termination appears to crucially involve depletion of Ca2+ in the lumen of the sarcoplasmic reticulum (SR), but in skeletal muscle, the mechanism is unknown. We used SEER (shifted excitation and emission ratioing of fluorescence) of SR-trapped mag-indo-1 and confocal imaging of fluorescence of cytosolic rhod-2 to image Ca2+ sparks while reversibly changing and measuring [Ca2+] in the SR ([Ca2+]SR) of membrane-permeabilized frog skeletal muscle cells. Sparks were collected in cells immersed in a solution promoting production of events at moderate frequency. Just after permeabilization, event frequency was zero, and in 10 minutes it reached close to a steady value. Controlled interventions modified [Ca2+]SR reversibly between a low value (299 μM on average in 10 experiments) and a high value (433 μM, a 45% average increase). This change increased sparks frequency by 93%, spatial width by 7%, rise time by 10%, and peak amplitude by 38% (provided that it was calculated in absolute terms, rather than normalized by resting fluorescence). The changes in event frequency and amplitude were statistically significant. The “strength” of the effect of [Ca2+]SR on frequency, quantified by decomposition of variance, was <6%. While the average change in [Ca2+]SR was limited, it reached up to 200% in individual fibers, without causing massive Ca2+ release or an increase of >3.5-fold in event frequency. Taken together with existing evidence that depletion is modest during Ca2+ sparks or release elicited by an action potential, the mild effects of [Ca2+]SR reported here do not support a major role of depletion in either the termination of sparks or the strong inactivation that terminates Ca2+ release at the global level in frog skeletal muscle.

Hg2+-induced contracture in mechanically skinned fibers of frog skeletal muscle

1985 ◽  
Vol 63 (9) ◽  
pp. 1070-1074 ◽  
Author(s):  
Takako Aoki ◽  
Toshiharu Oba ◽  
Ken Hotta
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Sulfhydryl Groups ◽  
Skinned Fibers ◽  
Frog Skeletal Muscle ◽  
Semitendinosus Muscle ◽  
Skinned Fiber ◽  
Brij 58 ◽  
Develop Tension

In mechanically skinned fibers of the semitendinosus muscle of bullfrogs, we examined the role of membrane sulfhydryl groups on Ca2+ release from the sarcoplasmic reticulum (SR). Hg2+, a sulfhydryl reagent (20–100 μM), induced a repetitive contracture of skinned fibers, and this contracture did not occur in skinned fibers in which the SR had been disrupted by treatment with a detergent (Brij 58). Procaine (10 mM), Mg2+ (5 mM), or dithiothreitol (1 mM) blocked the Hg2+-induced contracture. Ag+ or p-chloromercuribenzenesulfonic acid produced similar contractures to that induced by Hg2+. We conclude that Hg2+ releases Ca2+ from SR of a skinned fiber by modifying sulfhydryl groups on the SR membrane, and suggest that the Ca2+ released by Hg2+ may trigger a greater release of Ca2+ from SR to develop tension.

scholarly journals Kinetics of contractile activation in voltage clamped frog skeletal muscle fibers

1997 ◽  
Vol 73 (4) ◽  
pp. 1999-2011 ◽  
Author(s):  
P. Szentesi ◽  
Z. Papp ◽  
G. Szücs ◽  
L. Kovács ◽  
L. Csernoch
Keyword(s):  
Skeletal Muscle ◽  
Muscle Fibers ◽  
Frog Skeletal Muscle ◽  
Skeletal Muscle Fibers ◽  
Contractile Activation ◽  
Kinetics Of

scholarly journals Modulation of the Frequency of Spontaneous Sarcoplasmic Reticulum Ca2+ Release Events (Ca2+ Sparks) by Myoplasmic [Mg2+] in Frog Skeletal Muscle

1998 ◽  
Vol 111 (2) ◽  
pp. 207-224 ◽  
Author(s):  
Alain Lacampagne ◽  
Michael G. Klein ◽  
Martin F. Schneider
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Calcium Release ◽  
Frog Skeletal Muscle ◽  
Calcium Release Channel ◽  
Release Channel ◽  
Event Frequency ◽  
Open Time ◽  
Channel Opening ◽  
Sr Calcium Release

The modulation by internal free [Mg2+] of spontaneous calcium release events (Ca2+ “sparks”) from the sarcoplasmic reticulum (SR) was studied in depolarized notched frog skeletal muscle fibers using a laser scanning confocal microscope in line-scan mode (x vs. t). Over the range of [Mg2+] from 0.13 to 1.86 mM, decreasing the [Mg2+] induced an increase in the frequency of calcium release events in proportion to [Mg2+]−1.6. The change of event frequency was not due to changes in [Mg-ATP] or [ATP]. Analysis of individual SR calcium release event properties showed that the variation in event frequency induced by the change of [Mg2+] was not accompanied by any changes in the spatiotemporal spread (i.e., spatial half width or temporal half duration) of Ca2+ sparks. The increase in event frequency also had no effect on the distribution of event amplitudes. Finally, the rise time of calcium sparks was independent of the [Mg2+], indicating that the open time of the SR channel or channels underlying spontaneous calcium release events was not altered by [Mg2+] over the range tested. These results suggest that in resting skeletal fibers, [Mg2+] modulates the SR calcium release channel opening frequency by modifying the average closed time of the channel without altering the open time. A kinetic reaction scheme consistent with our results and those of bilayer and SR vesicle experiments indicates that physiological levels of resting Mg2+ may inhibit channel opening by occupying the site for calcium activation of the SR calcium release channel.

Differential Ca2+ sensitivity of skeletal and cardiac muscle ryanodine receptors in the presence of calmodulin

2000 ◽  
Vol 279 (3) ◽  
pp. C724-C733 ◽  
Author(s):  
Bradley R. Fruen ◽  
Jennifer M. Bardy ◽  
Todd M. Byrem ◽  
Gale M. Strasburg ◽  
Charles F. Louis
Keyword(s):  
Skeletal Muscle ◽  
Sarcoplasmic Reticulum ◽  
Cardiac Muscle ◽  
Ryanodine Receptors ◽  
Cross Linking ◽  
Release Channel ◽  
Channel Activation ◽  
Functional Interactions ◽  
Ryr2 Channel

Calmodulin (CaM) activates the skeletal muscle ryanodine receptor Ca2+ release channel (RyR1) in the presence of nanomolar Ca2+ concentrations. However, the role of CaM activation in the mechanisms that control Ca2+ release from the sarcoplasmic reticulum (SR) in skeletal muscle and in the heart remains unclear. In media that contained 100 nM Ca2+, the rate of45Ca2+ release from porcine skeletal muscle SR vesicles was increased approximately threefold in the presence of CaM (1 μM). In contrast, cardiac SR vesicle45Ca2+ release was unaffected by CaM, suggesting that CaM activated the skeletal RyR1 but not the cardiac RyR2 channel isoform. The activation of RyR1 by CaM was associated with an approximately sixfold increase in the Ca2+ sensitivity of [3H]ryanodine binding to skeletal muscle SR, whereas the Ca2+ sensitivity of cardiac SR [3H]ryanodine binding was similar in the absence and presence of CaM. Cross-linking experiments identified both RyR1 and RyR2 as predominant CaM binding proteins in skeletal and cardiac SR, respectively, and [35S]CaM binding determinations further indicated comparable CaM binding to the two isoforms in the presence of micromolar Ca2+. In nanomolar Ca2+, however, the affinity and stoichiometry of RyR2 [35S]CaM binding was reduced compared with that of RyR1. Together, our results indicate that CaM activates RyR1 by increasing the Ca2+ sensitivity of the channel, and further suggest differences in CaM's functional interactions with the RyR1 and RyR2 isoforms that may potentially contribute to differences in the Ca2+ dependence of channel activation in skeletal and cardiac muscle.

Role of Parvalbumin in Skeletal Muscle Relaxation

Physiology ◽  
1996 ◽  
Vol 11 (6) ◽  
pp. 249-255 ◽  
Author(s):  
JA Rall
Keyword(s):  
Skeletal Muscle ◽  
Skeletal Muscles ◽  
Muscle Relaxation ◽  
Calcium Pump ◽  
Frog Skeletal Muscle ◽  
Animal Kingdom ◽  
Calcium Buffer ◽  
High Concentrations ◽  
Sarcoplasmic Reticulum Calcium

Parvalbumin, a soluble intracellular calcium buffer, is present in high concentrations in fast-contracting skeletal muscles across the animal kingdom. In frog skeletal muscle, pharmacological or low-temperature inhibition of the sarcoplasmic reticulum calcium pump reveals that parvalbumin sequesters calcium and promotes relaxation at a rate determined by magnesium dissociation from parvalbumin.

Adrenaline causes potassium influx in skeletal muscle and potassium efflux in cardiac muscle in rats: The role of NA/K ATPase

Life Sciences ◽  
1987 ◽  
Vol 40 (1) ◽  
pp. 101-108 ◽  
Author(s):  
A.D. Struthers ◽  
D.L. Davies ◽  
D. Harland ◽  
J.S. Price ◽  
R.A. Brown ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Cardiac Muscle ◽  
Potassium Efflux ◽  
Potassium Influx

scholarly journals Lmo7 is dispensable for skeletal muscle and cardiac function

2015 ◽  
Vol 309 (7) ◽  
pp. C470-C479 ◽  
Author(s):  
Dieu Hung Lao ◽  
Mary C. Esparza ◽  
Shannon N. Bremner ◽  
Indroneal Banerjee ◽  
Jianlin Zhang ◽  
...  
Keyword(s):  
Skeletal Muscle ◽  
Muscular Dystrophy ◽  
Cardiac Function ◽  
Cardiac Muscle ◽  
Mapk Pathway ◽  
Mdx Mouse ◽  
Mdx Mice ◽  
Mouse Line

Emery-Dreifuss muscular dystrophy (EDMD) is a degenerative disease primarily affecting skeletal muscles in early childhood as well as cardiac muscle at later stages. EDMD is caused by a number of mutations in genes encoding proteins associated with the nuclear envelope (e.g., Emerin, Lamin A/C, and Nesprin). Recently, a novel protein, Lim-domain only 7 ( lmo7) has been reported to play a role in the molecular pathogenesis of EDMD. Prior in vitro and in vivo studies suggested the intriguing possibility that Lmo7 plays a role in skeletal or cardiac muscle pathophysiology. To further understand the in vivo role of Lmo7 in striated muscles, we generated a novel Lmo7-null ( lmo7−/−) mouse line. Using this mouse line, we examined skeletal and cardiac muscle physiology, as well as the role of Lmo7 in a model of muscular dystrophy and regeneration using the dystrophin-deficient mdx mouse model. Our results demonstrated that lmo7−/− mice had no abnormalities in skeletal muscle morphology, physiological function, or regeneration. Cardiac function was also unaffected. Moreover, we found that ablation of lmo7 in mdx mice had no effect on the observed myopathy and muscular regeneration exhibited by mdx mice. Molecular analyses also showed no changes in dystrophin complex factors, MAPK pathway components, and Emerin levels in lmo7 knockout mice. Taken together, we conclude that Lmo7 is dispensable for skeletal muscle and cardiac physiology and pathophysiology.

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