title: Individual Cardiac Mitochondria Undergo Rare Transient Permeability Transition Pore Openings.
abstract: BACKGROUND
  Mitochondria produce ATP, especially critical for survival of highly aerobic cells, such as cardiac myocytes. Conversely, opening of mitochondrial high-conductance and long-lasting permeability transition pores (mPTP) causes respiratory uncoupling, mitochondrial injury, and cell death. However, low conductance and transient mPTP openings (tPTP) might limit mitochondrial Ca(2+) load and be cardioprotective, but direct evidence for tPTP in cells is limited.
  
  
  OBJECTIVE
  To directly characterize tPTP occurrence during sarcoplasmic reticulum Ca(2+) release in adult cardiac myocytes.
  
  
  RESULTS
  Here, we measured tPTP directly as transient drops in mitochondrial [Ca(2+)] ([Ca(2+)]mito) and membrane potential (ΔΨm) in adult cardiac myocytes during cyclic sarcoplasmic reticulum Ca release, by simultaneous live imaging of 500 to 1000 individual mitochondria. The frequency of tPTPs rose at higher [Ca(2+)]mito, [Ca(2+)]i, with 1 μmol/L peroxide exposure and in myocyte from failing hearts. The tPTPs were suppressed by preventing mitochondrial Ca(2+) influx, by mPTP inhibitor cyclosporine A, sanglifehrin, and in cyclophilin D knockout mice. These tPTP events were 57±5 s in duration, but were rare (occurring in <0.1% of myocyte mitochondria at any moment) such that the overall energetic cost to the cell is minimal. The tPTP pore size is much smaller than for permanent mPTP, as neither Rhod-2 nor calcein (600 Da) were lost. Thus, proteins and even molecules the size of NADH (663 Da) will be retained during these tPTP.
  
  
  CONCLUSIONS
  We conclude that tPTP openings (MitoWinks) may be molecularly related to pathological mPTP, but are likely to be normal physiological manifestation that benefits mitochondrial (and cell) survival by allowing individual mitochondria to reset themselves with little overall energetic cost.
authors.affiliation: From the Department of Pharmacology, University of California, Davis (X.L., D.M.B.); Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, OH (J.Q.K., J.D.M.).
authors.forename: Xiyuan
authors.initials: X
authors.lastname: Lu
authors.affiliation: From the Department of Pharmacology, University of California, Davis (X.L., D.M.B.); Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, OH (J.Q.K., J.D.M.).
authors.forename: Jennifer Q
authors.initials: JQ
authors.lastname: Kwong
authors.affiliation: From the Department of Pharmacology, University of California, Davis (X.L., D.M.B.); Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, OH (J.Q.K., J.D.M.).
authors.forename: Jeffery D
authors.initials: JD
authors.lastname: Molkentin
authors.affiliation: From the Department of Pharmacology, University of California, Davis (X.L., D.M.B.); Department of Pediatrics, Cincinnati Children's Hospital Medical Center, University of Cincinnati, OH (J.Q.K., J.D.M.). dmbers@ucdavis.edu.
authors.forename: Donald M
authors.initials: DM
authors.lastname: Bers
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D051379:Mice; D008810:Mice, Inbred C57BL; D008929:Mitochondria, Heart / Q000378:metabolism*; D033681:Mitochondrial Membrane Transport Proteins / Q000378:metabolism*; D032383:Myocytes, Cardiac / Q000378:metabolism*; D010539:Permeability
chemical_list: D033681:Mitochondrial Membrane Transport Proteins
keywords: calcium; cardiac myocytes; cyclosporine; metabolism; mitochondria