title: Mitochondrial calcium uptake regulates rapid calcium transients in skeletal muscle during excitation-contraction (E-C) coupling.
abstract: Defective coupling between sarcoplasmic reticulum and mitochondria during control of intracellular Ca(2+) signaling has been implicated in the progression of neuromuscular diseases. Our previous study showed that skeletal muscles derived from an amyotrophic lateral sclerosis (ALS) mouse model displayed segmental loss of mitochondrial function that was coupled with elevated and uncontrolled sarcoplasmic reticulum Ca(2+) release activity. The localized mitochondrial defect in the ALS muscle allows for examination of the mitochondrial contribution to Ca(2+) removal during excitation-contraction coupling by comparing Ca(2+) transients in regions with normal and defective mitochondria in the same muscle fiber. Here we show that Ca(2+) transients elicited by membrane depolarization in fiber segments with defective mitochondria display an ~10% increased amplitude. These regional differences in Ca(2+) transients were abolished by the application of 1,2-bis(O-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid, a fast Ca(2+) chelator that reduces mitochondrial Ca(2+) uptake. Using a mitochondria-targeted Ca(2+) biosensor (mt11-YC3.6) expressed in ALS muscle fibers, we monitored the dynamic change of mitochondrial Ca(2+) levels during voltage-induced Ca(2+) release and detected a reduced Ca(2+) uptake by mitochondria in the fiber segment with defective mitochondria, which mirrored the elevated Ca(2+) transients in the cytosol. Our study constitutes a direct demonstration of the importance of mitochondria in shaping the cytosolic Ca(2+) signaling in skeletal muscle during excitation-contraction coupling and establishes that malfunction of this mechanism may contribute to neuromuscular degeneration in ALS.
authors.affiliation: Department of Molecular Biophysics and Physiology, Rush University School of Medicine, Chicago, Illinois 60612, USA.
authors.forename: Jianxun
authors.initials: J
authors.lastname: Yi
authors.forename: Changling
authors.initials: C
authors.lastname: Ma
authors.forename: Yan
authors.initials: Y
authors.lastname: Li
authors.forename: Noah
authors.initials: N
authors.lastname: Weisleder
authors.forename: Eduardo
authors.initials: E
authors.lastname: Ríos
authors.forename: Jianjie
authors.initials: J
authors.lastname: Ma
authors.forename: Jingsong
authors.initials: J
authors.lastname: Zhou
mesh_terms: D000690:Amyotrophic Lateral Sclerosis / Q000378:metabolism / Q000473:pathology; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D002614:Chelating Agents / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004195:Disease Models, Animal; D004533:Egtazic Acid / Q000031:analogs & derivatives / Q000494:pharmacology; D056966:Excitation Contraction Coupling; D008564:Membrane Potentials; D051379:Mice; D008817:Mice, Mutant Strains; D008931:Mitochondria, Muscle / Q000378:metabolism* / Q000473:pathology; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000473:pathology; D012519:Sarcoplasmic Reticulum / Q000378:metabolism / Q000473:pathology
chemical_list: D002614:Chelating Agents; D004533:Egtazic Acid; C025603:1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid; D002118:Calcium