Alteration in calcium handling at the subcellular level in mdx myotubes.
In this study, we have tested the hypothesis that augmented [Ca(2+)] in subcellular regions or organelles, which are known to play a key role in cell survival, is the missing link between Ca(2+) homeostasis alterations and muscular degeneration associated with muscular dystrophy. To this end, different targeted chimeras of the Ca(2+)-sensitive photoprotein aequorin have been transiently expressed in subcellular compartments of skeletal myotubes of mdx mice, the animal model of Duchenne muscular dystrophy. Direct measurements of the [Ca(2+)] in the sarcoplasmic reticulum, [Ca(2+)](sr), show a higher steady state level at rest and a larger drop after KCl-induced depolarization in mdx compared with control myotubes. The peaks in [Ca(2+)] occurring in the mitochondrial matrix of mdx myotubes are significantly larger than in controls upon KCl-induced depolarization or caffeine application. The augmented response of mitochondria precedes the alterations in the Ca(2+) responses of the cytosol and of the cytoplasmic region beneath the membrane, which become significant only at a later stage of myotube differentiation. Taking into account the key role played by mitochondria Ca(2+) handling in the control of cell death, our data suggest that mitochondria are potential targets of impaired Ca(2+) homeostasis in muscular dystrophy.
Robert
V
V
Department of Biomedical Sciences, CNR Center of Biomembranes, University of Padova, 35131 Padua, Italy.
Massimino
M L
ML
Tosello
V
V
Marsault
R
R
Cantini
M
M
Sorrentino
V
V
Pozzan
T
T
D000331:Aequorin / Q000235:genetics; D000818:Animals; D000831:Animals, Newborn; D002118:Calcium / Q000378:metabolism*; D002451:Cell Compartmentation; D002478:Cells, Cultured; D051379:Mice; D018101:Mice, Inbred mdx; D008928:Mitochondria / Q000378:metabolism; D018482:Muscle, Skeletal / Q000196:embryology / Q000378:metabolism*; D020388:Muscular Dystrophy, Duchenne / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D014162:Transfection
D000331:Aequorin; D002118:Calcium