Assessment of calcium sparks in intact skeletal muscle fibers
Journal of Visualized Experiments: JoVE, 2014•pmc.ncbi.nlm.nih.gov
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+ handling
properties of healthy and diseased striated muscles. Although Ca2+ sparks events are …
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+ handling
properties of healthy and diseased striated muscles. Although Ca2+ sparks events are …
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+ 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).
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