title: Dynamic modulation of Ca2+ sparks by mitochondrial oscillations in isolated guinea pig cardiomyocytes under oxidative stress.
abstract: Local control of Ca(2+)-induced Ca(2+) release (CICR) depends on the spatial organization of L-type Ca(2+) channels and ryanodine receptors (RyR) in the dyad. Analogously, Ca(2+) uptake by mitochondria is facilitated by their close proximity to the Ca(2+) release sites, a process required for stimulating oxidative phosphorylation during changes in work. Mitochondrial feedback on CICR is less well understood. Since mitochondria are a primary source of reactive oxygen species (ROS), they could potentially influence the cytosolic redox state, in turn altering RyR open probability. We have shown that self-sustained oscillations in mitochondrial inner membrane potential (ΔΨ(m)), NADH, ROS, and reduced glutathione (GSH) can be triggered by a laser flash in cardiomyocytes. Here, we employ this method to directly examine how acute changes in energy state dynamically influence resting Ca(2+) spark occurrence and properties. Two-photon laser scanning microscopy was used to monitor cytosolic Ca(2+) (or ROS), ΔΨ(m), and NADH (or GSH) simultaneously in isolated guinea pig cardiomyocytes. Resting Ca(2+) spark frequency increased with each ΔΨ(m) depolarization and decreased with ΔΨ(m) repolarization without affecting Ca(2+) spark amplitude or time-to-peak. Stabilization of mitochondrial energetics by pretreatment with the superoxide scavenger TMPyP, or by acute addition of 4'-chlorodiazepam, a mitochondrial benzodiazepine receptor antagonist that blocks the inner membrane anion channel, prevented or reversed, respectively, the increased spark frequency. Cyclosporine A did not block the ΔΨ(m) oscillations or prevent Ca(2+) spark modulation by ΔΨ(m). The results support the hypothesis that mitochondria exert an influential role on the redox environment of the Ca(2+) handling subsystem, with mechanistic implications for the pathophysiology of cardiac disease.
authors.affiliation: Department of Medicine, Division of Cardiology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Lufang
authors.initials: L
authors.lastname: Zhou
authors.forename: Miguel A
authors.initials: MA
authors.lastname: Aon
authors.forename: Ting
authors.initials: T
authors.lastname: Liu
authors.forename: Brian
authors.initials: B
authors.lastname: O'Rourke
mesh_terms: D000818:Animals; D001570:Benzodiazepinones / Q000494:pharmacology; D002118:Calcium / Q000378:metabolism*; D020746:Calcium Channels, L-Type / Q000502:physiology*; D016166:Free Radical Scavengers / Q000494:pharmacology; D058787:GABA-A Receptor Antagonists / Q000494:pharmacology; D005978:Glutathione / Q000378:metabolism; D006168:Guinea Pigs; D006331:Heart Diseases / Q000378:metabolism* / Q000473:pathology; D015640:Ion Channel Gating / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D007834:Lasers; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects / Q000502:physiology* / Q000528:radiation effects; D018613:Microscopy, Confocal; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism* / Q000528:radiation effects; D009243:NAD / Q000378:metabolism; D010084:Oxidation-Reduction; D018384:Oxidative Stress; D017785:Photons; D011166:Porphyrins / Q000494:pharmacology; D017382:Reactive Oxygen Species / Q000037:antagonists & inhibitors / Q000378:metabolism; D011963:Receptors, GABA-A / Q000378:metabolism; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D014466:Ultraviolet Rays
chemical_list: D001570:Benzodiazepinones; D020746:Calcium Channels, L-Type; D016166:Free Radical Scavengers; D058787:GABA-A Receptor Antagonists; D011166:Porphyrins; D017382:Reactive Oxygen Species; D011963:Receptors, GABA-A; D019837:Ryanodine Receptor Calcium Release Channel; D009243:NAD; C028513:4'-chlorodiazepam; C021096:tetra(4-N-methylpyridyl)porphine; D005978:Glutathione; D002118:Calcium