title: Mitochondria fine-tune the slow Ca(2+) transients induced by electrical stimulation of skeletal myotubes.
abstract: Mitochondria sense cytoplasmic Ca(2+) signals in many cell types. In mammalian skeletal myotubes, depolarizing stimuli induce two independent cytoplasmic Ca(2+) signals: a fast signal associated with contraction and a slow signal that propagates to the nucleus and regulates gene expression. How mitochondria sense and possibly affect these cytoplasmic Ca(2+) signals has not been reported. We investigated here (a) the emergence of mitochondrial Ca(2+) signals in response to electrical stimulation of myotubes, (b) the contribution of mitochondrial Ca(2+) transients to ATP generation and (c) the influence of mitochondria as modulators of cytoplasmic and nuclear Ca(2+) signals. Rhod2 and Fluo3 fluorescence determinations revealed composite Ca(2+) signals associated to the mitochondrial compartment in electrically stimulated (400 pulses, 45 Hz) skeletal myotubes. Similar Ca(2+) signals were detected when using a mitochondria-targeted pericam. The fast mitochondrial Ca(2+) rise induced by stimulation was inhibited by pre-incubation with ryanodine, whereas the phospholipase C inhibitor U73122 blocked the slow mitochondrial Ca(2+) signal, showing that mitochondria sense the two cytoplasmic Ca(2+) signal components. The fast but not the slow Ca(2+) transient enhanced mitochondrial ATP production. Inhibition of the mitochondrial Ca(2+) uniporter prevented the emergence of mitochondrial Ca(2+) transients and significantly increased the magnitude of slow cytoplasmic Ca(2+) signals after stimulation. Precluding mitochondrial Ca(2+) extrusion with the Na(+)/Ca(2+) exchanger inhibitor CGP37157 decreased mitochondrial potential, increased the magnitude of the slow cytoplasmic Ca(2+) signal and decreased the rate of Ca(2+) signal propagation from one nucleus to the next. Over expression of the mitochondrial fission protein Drp-1 decreased mitochondrial size and the slow Ca(2+) transient in mitochondria, but enhanced cytoplasmic and nuclear slow transients. The present results indicate that mitochondria play a central role in the regulation of Ca(2+) signals involved in gene expression in myotubes.
authors.affiliation: Centro de Estudios Moleculares de la Celula, Universidad de Chile, Instituto de Ciencias Biomédicas, Facultad de Medicina, Santiago 8380492, Chile.
authors.forename: Veronica
authors.initials: V
authors.lastname: Eisner
authors.forename: Valentina
authors.initials: V
authors.lastname: Parra
authors.forename: Sergio
authors.initials: S
authors.lastname: Lavandero
authors.forename: Cecilia
authors.initials: C
authors.lastname: Hidalgo
authors.forename: Enrique
authors.initials: E
authors.lastname: Jaimovich
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis; D000818:Animals; D002118:Calcium / Q000378:metabolism; D020013:Calcium Signaling; D002478:Cells, Cultured; D004558:Electric Stimulation; D007700:Kinetics; D008931:Mitochondria, Muscle / Q000502:physiology*; D018485:Muscle Fibers, Skeletal / Q000502:physiology*; D051381:Rats
chemical_list: D000255:Adenosine Triphosphate; D002118:Calcium