Name: assessment of calcium sparks in intact skeletal muscle fibers
Uploaded: 2014-02-24T15:00:00
Description: Watch this Scientific Journal Video about Assessment of Calcium Sparks in Intact Skeletal Muscle Fibers at JoVE.com

This work was supported by RO1- AG028614 to JM, RO1- AR063084to NLW, and RO1-AR057404 to JZ.

1. Setting up Osmotic-stress Perfusion System
Figure 1 is a schematic protocol of calcium sparks assessment in intact skeletal muscle fibers.
<ol>
	<li>Set up a three-axis (xyz) micromanipulator capable of positioning the outlet tip of the perfusion system containing a minimum of two channels. This could be made with disposable Luer-syringe barrel with attached three-way Luer-Lok&#160;stopcock to switch on and/or off of the flow of perfusi...

<ol>
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M., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reciprocal+amplification+of+ROS+and+Ca2++signals+in+stressed+mdx+dystrophic+skeletal+muscle+fibers.">Reciprocal amplification of ROS and Ca2+ signals in stressed mdx dystrophic skeletal muscle fibers.</a> Pflugers. Arch. 458 (5), 915-928 (2009).</li><li>Lovering, R. M., Michaelson, L., Ward, C. W., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Malformed+mdx+myofibers+have+normal+cytoskeletal+architecture+yet+altered+EC+coupling+and+stress-induced+Ca2++signaling.">Malformed mdx myofibers have normal cytoskeletal architecture yet altered EC coupling and stress-induced Ca2+ signaling.</a> Am. J. Physiol. Cell. Physiol. 297 (3), 571-580 (2009).</li><li>Weisleder, N., Ma, J. 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Chem. 286 (37), 32436-32443 (2011).</li><li>Tjondrokoesoemo, A., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Type+1+inositol+(1,4,5)-trisphosphate+receptor+activates+ryanodine+receptor+1+to+mediate+calcium+spark+signaling+in+adult+Mammalian+skeletal+muscle.">Type 1 inositol (1,4,5)-trisphosphate receptor activates ryanodine receptor 1 to mediate calcium spark signaling in adult Mammalian skeletal muscle.</a> J. Biol. Chem. 288, 2103-2109 (2013).</li><li>Martins, A. S., et al. <a target="_blank" href="http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=PubMed&cmd=Search&doptcmdl=Citation&defaultField=Title+Word&term=Reactive+oxygen+species+contribute+to+Ca2++signals+produced+by+osmotic+stress+in+mouse+skeletal+muscle+fibres.">Reactive oxygen species contribute to Ca2+ signals produced by osmotic stress in mouse skeletal muscle fibres.</a> J. 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This method of assessing Ca2+ sparks in intact skeletal muscle is a useful tool for muscle physiology and disease research. We showed that the Ca2+&#160;spark response was altered in different conditions, including muscular dystrophy11, aging18,19,&#160;as well as in amyotrophic lateral sclerosis20. Our recent study also revealed functional coupling between IP3 receptor and RyR representing a critical component that contributes to Ca<...

Intracellular free Ca2+ ([Ca2+]i) is a versatile and important secondary messenger that regulates multiple cellular functions in excitable cells such as neurons, cardiac, skeletal and smooth muscles (for review see&#160;Stutzmann&#160;and Mattson1). Regulated Ca2+ mobilization and cross-talk between sarcoplasmic reticulum (SR) and T-tubule (TT) membranes are fundamental regulators of muscle physiology. Furthermore, changes in Ca2+ signaling had been shown to be an underlying mechanism of contractile dysfunction in various muscle diseases.
Ca2+ sparks are localized elementary Ca2+ release events originating from opening of the ryanodine receptor (RyR) channel on the sarcoplasmic reticulum (SR) membrane2. In cardiac muscle, sparks occur spontaneously through opening of the RyR2 channel by a Ca2+-induced Ca2+&#160;release (CICR) mechanism 3-5. In skeletal muscle, RyR1 is strictly controlled by the voltage sensor at the TT membrane6,7. Thus Ca2+ sparks are suppressed and rarely detected in resting conditions in intact skeletal muscle fibers. Until recently, the sarcolemmal membrane needed to be disrupted by various chemical or mechanical &#34;skinning&#34; methods to uncouple the suppression of the voltage sensor on RyR1 and allowed for Ca2+ spark events to be detected in skeletal muscle8,9. One method previously described required permeabilization of the membrane of muscle fibers by saponin detergent10.
In 2003, we discovered that either transient hypoosmotic stress or hyperosmotic stress could induce peripheral Ca2+ sparks adjacent to the sarcolemmal membrane in intact muscle fibers11. This method has since been modified to study the molecular mechanism and modulation of Ca2+ release and dynamics12-16. Here we outline the details of our experimental approach for induction, detection and analysis of Ca2+ sparks in intact skeletal muscle. We also present our custom-built spark analysis program that can be used to quantify the elemental properties of individual Ca2+ sparks in skeletal muscle, e.g. spark frequency and amplitude (&#916; F/F0, which reflects the open probability of the RyR channels and the Ca2+ load inside the SR); time to peak (rise time) and duration (FDHM, full duration at half-maximal amplitude) of sparks, as well as the spatial distribution of Ca2+ sparks. In addition, we present evidence that links altered Ca2+ sparks to the various pathophysiological states in skeletal muscle, such as muscular dystrophy and amyotrophic lateral sclerosis.
The advantage of this technique involves the ability to measure Ca2+ in relatively undamaged cells, instead of stripping the muscle fibers, allowing recording of Ca2+ sparks in conditions closer to physiologic. Additionally, our custom-designed program provides more accurate calculations of the properties of the spark in relation to muscle fibers.

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		<col />
		<col />
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	<tbody>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">Dissecting microscope</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td style="width:367px;">Dissect out fibers and check muscle integrity</td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:195px;">Dissection tools -scissors, and fine tip forceps</td>
			<td style="width:111px;">Fine Science Tools</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:195px;">Sylgard 184 Silicone Elastomer Kit</td>
			<td>DOW CORNING</td>
			<td style="width:119px;">184 SIL ELAST KIT</td>
			<td style="width:367px;">&#160;Make ahead of time for fiber dissection. Mix 5 ml liquid Sylgard components and pour into a 60-mm glass Petri dish and waiting 48 hr to let the Sylgard compound become clear, colorless solid substrate.&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">60-mm glass petri dish&#160;</td>
			<td style="width:111px;">Pyrex</td>
			<td style="width:119px;">3160</td>
			<td>Fiber dissection</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Isotonic Tyrode Solution&#160;</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">Minimal Ca2+ Tyrode Solution</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Hypotonic Tyrode Solution&#160;</td>
			<td>Sigma-Aldrich</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">collagenase type I&#160;</td>
			<td>Sigma-Aldrich</td>
			<td>C-5138</td>
			<td>Fiber digestion&#160;</td>
		</tr>
		<tr height="23">
			<td height="23" style="height:23px;">Fluo-4 AM&#160;</td>
			<td style="width:111px;">Invitrogen</td>
			<td>F14201</td>
			<td>Fluorescent Ca2+ imaging dyes&#160;</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">TMRE</td>
			<td style="width:111px;">Invitrogen</td>
			<td>T669</td>
			<td>mitochondrial membrane potential fluorescent dyes</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;">Delta TPG dishes&#160;</td>
			<td>Bioptechs</td>
			<td style="width:119px;">0420041500C</td>
			<td>35 mm glass bottom dish for imaging</td>
		</tr>
		<tr height="21">
			<td height="21" style="height:21px;width:195px;">Spark Fit software</td>
			<td style="width:111px;"></td>
			<td style="width:119px;"></td>
			<td>data analysis software</td>
		</tr>
		<tr height="84">
			<td height="84" style="height:84px;width:195px;">Radiance 2100 laser scanning confocal microscope or equivalent microscope</td>
			<td style="width:111px;">Bio-Rad</td>
			<td style="width:119px;"></td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:195px;">3 axis micromanipulator</td>
			<td style="width:111px;">Narishige International</td>
			<td style="width:119px;">MHW-3</td>
			<td></td>
		</tr>
		<tr height="42">
			<td height="42" style="height:42px;width:195px;">temperature controllable orbital shaker</td>
			<td style="width:111px;">New Brunswick scientific</td>
			<td style="width:119px;"></td>
			<td>Fiber dissociation</td>
		</tr>
	</tbody>
</table>

assessment of calcium sparks in intact skeletal muscle fibers

Maintaining homeostatic Ca2+ signaling is a fundamental physiological process in living cells. Ca2+ sparks are the elementary units of Ca2+ signaling in the striated muscle fibers that appear as highly localized Ca2+ release events mediated by ryanodine receptor (RyR) Ca2+ release channels on the sarcoplasmic reticulum (SR) membrane. Proper assessment of muscle Ca2+ sparks could provide information on the intracellular Ca2+&#160;handling properties of healthy and diseased striated muscles. Although Ca2+ sparks events are commonly seen in resting cardiomyocytes, they are rarely observed in resting skeletal muscle fibers; thus there is a need for methods to generate and analyze sparks in skeletal muscle fibers.
Detailed here is an experimental protocol for measuring Ca2+ sparks in isolated flexor digitorm brevis (FDB) muscle fibers using fluorescent Ca2+ indictors and laser scanning confocal microscopy. In this approach, isolated FDB fibers are exposed to transient hypoosmotic stress followed by a return to isotonic physiological solution. Under these conditions, a robust Ca2+ sparks response is detected adjacent to the sarcolemmal membrane in young healthy FDB muscle fibers. Altered Ca2+ sparks response is detected in dystrophic or aged skeletal muscle fibers. This approach has recently demonstrated that membrane-delimited signaling involving cross-talk between inositol (1,4,5)-triphosphate receptor (IP3R) and RyR contributes to Ca2+ spark activation in skeletal muscle. In summary, our studies using osmotic stress induced Ca2+ sparks showed that this intracellular response reflects a muscle signaling mechanism in physiology and aging/disease states, including mouse models of muscle dystrophy (mdx mice) or amyotrophic lateral sclerosis (ALS model).

Earlier studies showed that transient hypoosmotic stress induced peripheral Ca2+ sparks adjacent to the sarcolemmal membrane in intact muscle fibers11. Figure 1 shows the images of intact single muscle fibers with smooth sarcolemmal membrane and characteristic clear striations. Figure 2 shows typical Ca2+ sparks (as xy images) were induced by transient (100 sec) treatment with a hypoosmotic solution that swells the FDB muscle fibers from young, h...

Watch this Scientific Journal Video about Assessment of Calcium Sparks in Intact Skeletal Muscle Fibers at JoVE.com

Assessment of Calcium Sparks in Intact Skeletal Muscle Fibers

Described here is a method to directly measure calcium sparks, the elementary units of Ca2+ release from sarcoplasmic reticulum&#160;in intact skeletal muscle fibers. This method utilizes osmotic-stress-mediated triggering of Ca2+ release from ryanodine receptor in isolated muscle fibers. The dynamics and homeostatic capacity of intracellular Ca2+ signaling can be employed to assess muscle function in health and disease.

Maintaining homeostatic Ca2+ signaling is a fundamental physiological process in living cells. Ca2+ sparks are the elementary units of Ca2+ signaling in ...

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