title: Calcium movement in cardiac mitochondria.
abstract: Existing theory suggests that mitochondria act as significant, dynamic buffers of cytosolic calcium ([Ca(2+)]i) in heart. These buffers can remove up to one-third of the Ca(2+) that enters the cytosol during the [Ca(2+)]i transients that underlie contractions. However, few quantitative experiments have been presented to test this hypothesis. Here, we investigate the influence of Ca(2+) movement across the inner mitochondrial membrane during both subcellular and global cellular cytosolic Ca(2+) signals (i.e., Ca(2+) sparks and [Ca(2+)]i transients, respectively) in isolated rat cardiomyocytes. By rapidly turning off the mitochondria using depolarization of the inner mitochondrial membrane potential (ΔΨm), the role of the mitochondria in buffering cytosolic Ca(2+) signals was investigated. We show here that rapid loss of ΔΨm leads to no significant changes in cytosolic Ca(2+) signals. Second, we make direct measurements of mitochondrial [Ca(2+)] ([Ca(2+)]m) using a mitochondrially targeted Ca(2+) probe (MityCam) and these data suggest that [Ca(2+)]m is near the [Ca(2+)]i level (∼100 nM) under quiescent conditions. These two findings indicate that although the mitochondrial matrix is fully buffer-capable under quiescent conditions, it does not function as a significant dynamic buffer during physiological Ca(2+) signaling. Finally, quantitative analysis using a computational model of mitochondrial Ca(2+) cycling suggests that mitochondrial Ca(2+) uptake would need to be at least ∼100-fold greater than the current estimates of Ca(2+) influx for mitochondria to influence measurably cytosolic [Ca(2+)] signals under physiological conditions. Combined, these experiments and computational investigations show that mitochondrial Ca(2+) uptake does not significantly alter cytosolic Ca(2+) signals under normal conditions and indicates that mitochondria do not act as important dynamic buffers of [Ca(2+)]i under physiological conditions in heart.
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland; Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Liron
authors.initials: L
authors.lastname: Boyman
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland; Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Aristide C
authors.initials: AC
authors.lastname: Chikando
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland; Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland; School of Systems Biology, George Mason University, Fairfax, Virginia.
authors.forename: George S B
authors.initials: GS
authors.lastname: Williams
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland; University of Maryland School of Nursing, Baltimore, Maryland; Department of Cell and Molecular Physiology, Loyola University Chicago, Maywood, Illinois.
authors.forename: Ramzi J
authors.initials: RJ
authors.lastname: Khairallah
authors.affiliation: Institute of Cardiovascular and Medical Sciences, University of Glasgow, G12 8QQ Glasgow, United Kingdom.
authors.forename: Sarah
authors.initials: S
authors.lastname: Kettlewell
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland; University of Maryland School of Nursing, Baltimore, Maryland.
authors.forename: Christopher W
authors.initials: CW
authors.lastname: Ward
authors.affiliation: Institute of Cardiovascular and Medical Sciences, University of Glasgow, G12 8QQ Glasgow, United Kingdom.
authors.forename: Godfrey L
authors.initials: GL
authors.lastname: Smith
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland; Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland.
authors.forename: Joseph P Y
authors.initials: JP
authors.lastname: Kao
authors.affiliation: Center for Biomedical Engineering and Technology, University of Maryland School of Medicine, Baltimore, Maryland; Department of Physiology, University of Maryland School of Medicine, Baltimore, Maryland. Electronic address: jlederer@umaryland.edu.
authors.forename: W Jonathan
authors.initials: WJ
authors.lastname: Lederer
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001692:Biological Transport; D020013:Calcium Signaling; D003600:Cytosol / Q000378:metabolism; D006352:Heart Ventricles / Q000166:cytology; D008929:Mitochondria, Heart / Q000378:metabolism*; D008954:Models, Biological; D032383:Myocytes, Cardiac / Q000166:cytology; D051381:Rats; D017382:Reactive Oxygen Species / Q000378:metabolism
chemical_list: D017382:Reactive Oxygen Species; D000255:Adenosine Triphosphate