title: Levosimendan improves calcium sensitivity of diaphragm muscle fibres from a rat model of heart failure.
abstract: OBJECTIVE
  Diaphragm muscle weakness occurs in patients with heart failure (HF) and is associated with exercise intolerance and increased mortality. Reduced sensitivity of diaphragm fibres to calcium contributes to diaphragm weakness in HF. Here we have investigated the ability of the calcium sensitizer levosimendan to restore the reduced calcium sensitivity of diaphragm fibres from rats with HF.
  
  
  METHODS
  Coronary artery ligation in rats was used as an animal model for HF. Sham-operated rats served as controls. Fifteen weeks after induction of HF or sham operations animals were killed and muscle fibres were isolated from the diaphragm. Diaphragm fibres were skinned and activated with solutions containing incremental calcium concentrations and 10 µM levosimendan or vehicle (0.02% DMSO). Developed force was measured at each calcium concentration, and force-calcium concentration relationships were plotted.
  
  
  RESULTS
  Calcium sensitivity of force generation was reduced in diaphragm muscle fibres from HF rats, compared with fibres from control rats (P < 0.01). Maximal force generation was ∼25% lower in HF diaphragm fibres than in control fibres (P < 0.05). Levosimendan significantly increased calcium sensitivity of force generation in diaphragm fibres from HF and control rats, without affecting maximal force generation.
  
  
  CONCLUSIONS
  Levosimendan enhanced the force generating capacity of diaphragm fibres from HF rats by increasing the sensitivity of force generation to calcium concentration. These results provide strong support for testing the effect of calcium sensitizers on diaphragm muscle weakness in patients with HF.
authors.affiliation: Department of Pulmonary Diseases, Institute for Fundamental and Clinical Human Movement Sciences, Radboud University Nijmegen Medical Centre, The Netherlands. h.vanhees@long.umcn.nl
authors.forename: H W H
authors.initials: HW
authors.lastname: van Hees
authors.forename: Gl
authors.initials: G
authors.lastname: Andrade Acuña
authors.forename: M
authors.initials: M
authors.lastname: Linkels
authors.forename: P N R
authors.initials: PN
authors.lastname: Dekhuijzen
authors.forename: L M A
authors.initials: LM
authors.lastname: Heunks
mesh_terms: D000818:Animals; D000889:Anti-Arrhythmia Agents / Q000494:pharmacology*; D002118:Calcium / Q000494:pharmacology*; D003964:Diaphragm / Q000187:drug effects / Q000502:physiology*; D006333:Heart Failure / Q000503:physiopathology*; D006801:Humans; D006835:Hydrazones / Q000494:pharmacology*; D008297:Male; D009119:Muscle Contraction / Q000187:drug effects*; D018485:Muscle Fibers, Skeletal / Q000737:chemistry / Q000187:drug effects* / Q000502:physiology; D018908:Muscle Weakness; D018995:Myosin Heavy Chains / Q000032:analysis; D011724:Pyridazines / Q000494:pharmacology*; D051381:Rats; D017208:Rats, Wistar; D000077464:Simendan
chemical_list: D000889:Anti-Arrhythmia Agents; D006835:Hydrazones; D011724:Pyridazines; D000077464:Simendan; D018995:Myosin Heavy Chains; D002118:Calcium