title: Impact of levosimendan and ischaemia-reperfusion injury on myocardial subsarcolemmal mitochondrial respiratory chain, mitochondrial membrane potential, Ca2+ cycling and ATP synthesis.
abstract: OBJECTIVE
  Levosimendan (LS) is increasingly used in case of myocardial failure after cardiac surgery. The impact of LS on myocardial mitochondrial functions, such as respiratory chain function (RCF), mitochondrial membrane potential (ΔΨm), Ca(2+) handling, mitochondrial permeability transition pore (mPTP) opening and ATP during ongoing ischaemia/reperfusion (IR) injury, is not well understood. Depending on LS, I/R injury or the combination of both, we analysed myocardial functions in a retrograde Langendorff-model followed by the analysis of subsarcolemmal mitochondrial (SSM) functions.
  
  
  METHODS
  Rat hearts were divided into four study groups; two were subjected to 30 min of perfusion without (control) or with the application of 1.4 µmol/20 min LS (Levo). Experiments were repeated with hearts being subjected to 40 min of normothermic stop-flow ischaemia and 30 min of reperfusion without (IR) or with LS application (Levo-IR). Systolic left ventricular pressure (LVPsys), left ventricular contractility (LVdp/dtmax) and coronary flow were determined. SSM were analysed regarding RCF, ΔΨm, ATP, and Ca(2+) retention capacity (CRC), Ca(2+)-induced swelling and Ca(2+) fluxes after (re)perfusion.
  
  
  RESULTS
  I/R injury suppressed LVdp/dtmax (1381 ± 927 vs 2464 ± 913 mmHg/s; P = 0.01 at 30 min (re-)perfusion time). IR revealed complex I-V state3 (19.1 ± 7.4 vs 27.6 ± 11.0 nmolO2/min; P < 0.044) and II-V state3 (20.6 ± 6.8 vs 37.3 ± 9.10 molO2/min; P < 0.0001) suppression and Levo limited I-V (14.8 ± 11.1 vs 27.6 ± 11.0 nmolO2/min; P < 0.001) and II-V (24.1 ± 6.4 vs 37.3 ± 9.10 molO2/min; P < 0.0001) function. After energizing, ΔΨm hypopolarization was observed in Levo (0.76 ± 0.04 vs 0.84 ± 0.04; P = 0.02), IR (0.75 ± 0.06 vs 0.84 ± 0.04; P = 0.007) and Levo-IR (0.75 ± 0.06 vs 0.06 ± 0.04; P = 0.01). IR (AUC: 626 vs 292; P = 0.023) and Levo-IR (AUC: 683 vs 292, P = 0.003) increased Ca(2+)-induced mPTP-opening susceptibility. CRC declined in IR (6.4 ± 2.1 vs 10.5 ± 2.6; P = 0.04) or Levo (6.5 ± 2.0 vs 10.5 ± 2.6; P = 0.023). Ca(2+) uptake was delayed in IR and Levo-IR without LS impact (P < 0.0001). Ca(2+) liberation was increased in Levo-IR. ATP synthesis was reduced in Levo (0.49 ± 0.14 vs 0.74 ± 0.14; P = 0.002) and Levo-I/R (0.34 ± 0.18 vs 0.74 ± 0.14; P < 0.002).
  
  
  CONCLUSIONS
  LS limited RCF at complex IV and V with ΔΨm hypopolarization suggesting a specific [Formula: see text]-dependent pathway. Ca(2+) redistribution from SSM by LS during I/R injury possibly prevents from Ca(2+) overload due to mPTP flickering. LS-induced mPTP flickering did not promote permanent Ca(2+)-induced mPTP opening. LS-dependent inhibition of ATP generation presumably resulted from complex IV and V limitations and lowered ΔΨm. However, a resulting impact of limited ATP synthesis on myocardial recovery remains arguable.
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Stefanie
authors.initials: S
authors.lastname: Sommer
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Marcus
authors.initials: M
authors.lastname: Leistner
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Ivan
authors.initials: I
authors.lastname: Aleksic
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Christoph
authors.initials: C
authors.lastname: Schimmer
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Khaled
authors.initials: K
authors.lastname: Alhussini
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Peer
authors.initials: P
authors.lastname: Kanofsky
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany.
authors.forename: Rainer G
authors.initials: RG
authors.lastname: Leyh
authors.affiliation: Department of Thoracic and Cardiovascular Surgery, University Hospital Würzburg, Würzburg, Germany Klinik f. Herz- und Gefäßchirurgie, Segeberger Kliniken, Bad Segeberg, Germany sommersebastianpatrick@freenet.de.
authors.forename: Sebastian-Patrick
authors.initials: SP
authors.lastname: Sommer
mesh_terms: D000255:Adenosine Triphosphate / Q000096:biosynthesis*; D000818:Animals; D015415:Biomarkers / Q000378:metabolism; D002118:Calcium / Q000378:metabolism; D002316:Cardiotonic Agents / Q000494:pharmacology*; D004579:Electron Transport / Q000187:drug effects; D006835:Hydrazones / Q000494:pharmacology*; D008297:Male; D053078:Membrane Potential, Mitochondrial / Q000187:drug effects; D008929:Mitochondria, Heart / Q000187:drug effects / Q000378:metabolism; D033681:Mitochondrial Membrane Transport Proteins / Q000187:drug effects / Q000378:metabolism; D000083162:Mitochondrial Permeability Transition Pore; D015428:Myocardial Reperfusion Injury / Q000503:physiopathology*; D011724:Pyridazines / Q000494:pharmacology*; D011897:Random Allocation; D017208:Rats, Wistar; D012508:Sarcolemma / Q000187:drug effects; D000077464:Simendan
chemical_list: D015415:Biomarkers; D002316:Cardiotonic Agents; D006835:Hydrazones; D033681:Mitochondrial Membrane Transport Proteins; D000083162:Mitochondrial Permeability Transition Pore; D011724:Pyridazines; D000077464:Simendan; D000255:Adenosine Triphosphate; D002118:Calcium
keywords: Ca2+; Ischaemia/reperfusion injury; Levosimendan; Mitochondria; Myocardium; ΔΨm