Dissociation of calmodulin from cardiac ryanodine receptor causes aberrant Ca(2+) release in heart failure.
OBJECTIVE
Calmodulin (CaM) is well known to modulate the channel function of the cardiac ryanodine receptor (RyR2). However, the possible role of CaM on the aberrant Ca(2+) release in diseased hearts remains unclear. In this study, we investigated the state of RyR2-bound CaM and channel dysfunctions in pacing-induced failing hearts.


RESULTS
The characteristics of CaM binding to RyR2 and the role of CaM on the aberrant Ca(2+) release were assessed in normal and failing canine hearts. The affinity of CaM binding to RyR2 was lower in failing sarcoplasmic reticulum (SR) than in normal SR. Addition of FK506, which dissociates FKBP12.6 from RyR2, to normal SR reduced the CaM-binding affinity. Dantrolene restored a normal level of the CaM-binding affinity in either FK506-treated (normal) SR or failing SR, suggesting that the defective inter-domain interaction between the N-terminal domain and the central domain of RyR2 (the therapeutic target of dantrolene) is involved in the reduction of the CaM-binding affinity in failing hearts. In saponin-permeabilized cardiomyocytes, the frequency of spontaneous Ca(2+) sparks was much more increased in failing cardiomyocytes than in normal cardiomyocytes, whereas the addition of a high concentration of CaM attenuated the aberrant increase of Ca(2+) sparks.


CONCLUSIONS
The defective inter-domain interaction between N-terminal and central domains within RyR2 reduces the binding affinity of CaM to RyR2, thereby causing the spontaneous Ca(2+) release events in failing hearts. Correction of the defective CaM binding may be a new strategy to protect against the aberrant Ca(2+) release in heart failure.
Ono
Makoto
M
Department of Medicine and Clinical Science, Division of Cardiology, Yamaguchi University Graduate School of Medicine, 1-1-1 Minamikogushi, Ube, Yamaguchi 755-8505, Japan.
Yano
Masafumi
M
Hino
Akihiro
A
Suetomi
Takeshi
T
Xu
Xiaojuan
X
Susa
Takehisa
T
Uchinoumi
Hitoshi
H
Tateishi
Hiroki
H
Oda
Tetsuro
T
Okuda
Shinichi
S
Doi
Masahiro
M
Kobayashi
Shigeki
S
Yamamoto
Takeshi
T
Koseki
Noritaka
N
Kyushiki
Hiroyuki
H
Ikemoto
Noriaki
N
Matsuzaki
Masunori
M
D000818:Animals; D020013:Calcium Signaling / Q000187:drug effects; D002147:Calmodulin / Q000378:metabolism*; D002304:Cardiac Pacing, Artificial; D003620:Dantrolene / Q000494:pharmacology; D004195:Disease Models, Animal; D004285:Dogs; D056966:Excitation Contraction Coupling; D006333:Heart Failure / Q000209:etiology / Q000378:metabolism*; D018613:Microscopy, Confocal; D009206:Myocardium / Q000378:metabolism*; D010446:Peptide Fragments / Q000378:metabolism; D011485:Protein Binding; D054730:Protein Interaction Domains and Motifs; D025941:Protein Interaction Mapping; D017434:Protein Structure, Tertiary; D019837:Ryanodine Receptor Calcium Release Channel / Q000378:metabolism*; D012519:Sarcoplasmic Reticulum / Q000187:drug effects / Q000378:metabolism*; D016559:Tacrolimus / Q000494:pharmacology; D022021:Tacrolimus Binding Proteins / Q000378:metabolism
D002147:Calmodulin; D010446:Peptide Fragments; D019837:Ryanodine Receptor Calcium Release Channel; C451408:ryanodine receptor calcium release channel (2460-2495), synthetic; D022021:Tacrolimus Binding Proteins; C403484:tacrolimus binding protein 1B; D003620:Dantrolene; D016559:Tacrolimus
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