title: A low-dose β1-blocker in combination with milrinone improves intracellular Ca2+ handling in failing cardiomyocytes by inhibition of milrinone-induced diastolic Ca2+ leakage from the sarcoplasmic reticulum.
abstract: OBJECTIVE
  The purpose of this study was to investigate whether adding a low-dose β1-blocker to milrinone improves cardiac function in failing cardiomyocytes and the underlying cardioprotective mechanism.
  
  
  BACKGROUND
  The molecular mechanism underlying how the combination of low-dose β1-blocker and milrinone affects intracellular Ca(2+) handling in heart failure remains unclear.
  
  
  METHODS
  We investigated the effect of milrinone plus landiolol on intracellular Ca(2+) transient (CaT), cell shortening (CS), the frequency of diastolic Ca(2+) sparks (CaSF), and sarcoplasmic reticulum Ca(2+) concentration ({Ca(2+)}SR) in normal and failing canine cardiomyocytes and used immunoblotting to determine the phosphorylation level of ryanodine receptor (RyR2) and phospholamban (PLB).
  
  
  RESULTS
  In failing cardiomyocytes, CaSF significantly increased, and peak CaT and CS markedly decreased compared with normal myocytes. Administration of milrinone alone slightly increased peak CaT and CS, while CaSF greatly increased with a slight increase in {Ca(2+)}SR. Co-administration of β1-blocker landiolol to failing cardiomyocytes at a dose that does not inhibit cardiomyocyte function significantly decreased CaSF with a further increase in {Ca(2+)}SR, and peak CaT and CS improved compared with milrinone alone. Landiolol suppressed the hyperphosphorylation of RyR2 (Ser2808) in failing cardiomyocytes but had no effect on levels of phosphorylated PLB (Ser16 and Thr17). Low-dose landiolol significantly inhibited the alternans of CaT and CS under a fixed pacing rate (0.5 Hz) in failing cardiomyocytes.
  
  
  CONCLUSIONS
  A low-dose β1-blocker in combination with milrinone improved cardiac function in failing cardiomyocytes, apparently by inhibiting the phosphorylation of RyR2, not PLB, and subsequent diastolic Ca(2+) leak.
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Shigeki
authors.initials: S
authors.lastname: Kobayashi
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Takehisa
authors.initials: T
authors.lastname: Susa
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Hironori
authors.initials: H
authors.lastname: Ishiguchi
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Takeki
authors.initials: T
authors.lastname: Myoren
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Wakako
authors.initials: W
authors.lastname: Murakami
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Takayoshi
authors.initials: T
authors.lastname: Kato
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Masakazu
authors.initials: M
authors.lastname: Fukuda
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Akihiro
authors.initials: A
authors.lastname: Hino
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Suetomi
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Makoto
authors.initials: M
authors.lastname: Ono
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Hitoshi
authors.initials: H
authors.lastname: Uchinoumi
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Hiroki
authors.initials: H
authors.lastname: Tateishi
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Mamoru
authors.initials: M
authors.lastname: Mochizuki
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Tetsuro
authors.initials: T
authors.lastname: Oda
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Shinichi
authors.initials: S
authors.lastname: Okuda
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Masahiro
authors.initials: M
authors.lastname: Doi
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Takeshi
authors.initials: T
authors.lastname: Yamamoto
authors.affiliation: Division of Cardiology, Department of Medicine and Clinical Science, Yamaguchi University Graduate School of Medicine, Ube, Japan.
authors.forename: Masafumi
authors.initials: M
authors.lastname: Yano
mesh_terms: D058671:Adrenergic beta-1 Receptor Antagonists / Q000494:pharmacology*; D000818:Animals; D002118:Calcium / Q000378:metabolism*; D020013:Calcium Signaling; D002316:Cardiotonic Agents / Q000494:pharmacology*; D002478:Cells, Cultured; D004285:Dogs; D020105:Milrinone / Q000494:pharmacology*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism*; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism; D012519:Sarcoplasmic Reticulum / Q000378:metabolism*
chemical_list: D058671:Adrenergic beta-1 Receptor Antagonists; D002316:Cardiotonic Agents; D019837:Ryanodine Receptor Calcium Release Channel; D020105:Milrinone; D002118:Calcium