title: While systolic cardiomyocyte function is preserved, diastolic myocyte function and recovery from acidosis are impaired in CaMKIIδ-KO mice.
abstract: OBJECTIVE
  CaMKII contributes to impaired contractility in heart failure by inducing SR Ca(2+)-leak. CaMKII-inhibition in the heart was suggested to be a novel therapeutic principle. Different CaMKII isoforms exist. Specifically targeting CaMKIIδ, the dominant isoform in the heart, could be of therapeutic potential without impairing other CaMKII isoforms.
  
  
  BACKGROUND
  We investigated whether cardiomyocyte function is affected by isoform-specific knockout (KO) of CaMKIIδ under basal conditions and upon stress, i.e. upon ß-adrenergic stimulation and during acidosis.
  
  
  RESULTS
  Systolic cardiac function was largely preserved in the KO in vivo (echocardiography) corresponding to unchanged Ca(2+)-transient amplitudes and isolated myocyte contractility in vitro. CaMKII activity was dramatically reduced while phosphatase-1 inhibitor-1 was significantly increased. Surprisingly, while diastolic Ca(2+)-elimination was slower in KO most likely due to decreased phospholamban Thr-17 phosphorylation, frequency-dependent acceleration of relaxation was still present. Despite decreased SR Ca(2+)-reuptake at lower frequencies, SR Ca(2+)-content was not diminished, which might be due to reduced diastolic SR Ca(2+)-loss in the KO as a consequence of lower RyR Ser-2815 phosphorylation. Challenging KO myocytes with isoproterenol showed intact inotropic and lusitropic responses. During acidosis, SR Ca(2+)-reuptake and SR Ca(2+)-loading were significantly impaired in KO, resulting in an inability to maintain systolic Ca(2+)-transients during acidosis and impaired recovery.
  
  
  CONCLUSIONS
  Inhibition of CaMKIIδ appears to be safe under basal physiologic conditions. Specific conditions exist (e.g. during acidosis) under which CaMKII-inhibition might not be helpful or even detrimental. These conditions will have to be more clearly defined before CaMKII inhibition is used therapeutically.
authors.affiliation: Dept. of Cardiology and Pneumology, Georg-August-University, Göttingen, Germany.
authors.forename: Stefan
authors.initials: S
authors.lastname: Neef
authors.forename: Can M
authors.initials: CM
authors.lastname: Sag
authors.forename: Maria
authors.initials: M
authors.lastname: Daut
authors.forename: Henrik
authors.initials: H
authors.lastname: Bäumer
authors.forename: Clemens
authors.initials: C
authors.lastname: Grefe
authors.forename: Ali
authors.initials: A
authors.lastname: El-Armouche
authors.forename: Jaime
authors.initials: J
authors.lastname: DeSantiago
authors.forename: Laetitia
authors.initials: L
authors.lastname: Pereira
authors.forename: Donald M
authors.initials: DM
authors.lastname: Bers
authors.forename: Johannes
authors.initials: J
authors.lastname: Backs
authors.forename: Lars S
authors.initials: LS
authors.lastname: Maier
mesh_terms: D000138:Acidosis / Q000378:metabolism*; D000818:Animals; D002118:Calcium / Q000378:metabolism; D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2 / Q000235:genetics / Q000378:metabolism*; D003971:Diastole / Q000235:genetics / Q000502:physiology; D056966:Excitation Contraction Coupling; D051379:Mice; D018345:Mice, Knockout; D032383:Myocytes, Cardiac / Q000166:cytology* / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000378:metabolism; D013599:Systole / Q000235:genetics / Q000502:physiology
chemical_list: D054732:Calcium-Calmodulin-Dependent Protein Kinase Type 2; D002118:Calcium