Defective regulation of interdomain interactions within the ryanodine receptor plays a key role in the pathogenesis of heart failure.
BACKGROUND
According to our hypothesis, 2 domains within the ryanodine receptor (RyR) of sarcoplasmic reticulum (SR) (N-terminal [0 to 600] and central [2000 to 2500] domains), where many mutations have been found in patients with polymorphic ventricular tachycardia, interact with each other as a regulatory switch for channel gating. Here, we investigated whether the defective FKBP12.6-mediated stabilization of RyR in heart failure is produced by an abnormal interdomain interaction.


RESULTS
SR vesicles were isolated from dog left ventricular muscles, and then the RyR moiety of the SR was fluorescently labeled with methylcoumarin acetate (MCA) using DPc10, a synthetic peptide corresponding to Gly2460-Pro2495 of RyR (one of the mutable domains in polymorphic ventricular tachycardia), as a site-directing carrier; the carrier was removed from the RyR after MCA labeling. Addition of DPc10 induced an unzipped state of the interacting N-terminal and central domains, as evidenced by an increase in the accessibility of the RyR-bound MCA fluorescence to a large fluorescence quencher. Domain unzipping resulted in Ca2+ leak through the RyR and facilitated cAMP-dependent hyperphosphorylation of RyR and FKBP12.6 dissociation from RyR. When DPc10 was introduced into the isolated myocytes, the magnitude of intracellular Ca2+ transient decreased, and its decay time was prolonged. In the SR isolated from pacing-induced dog failing hearts, the domain unzipping has already occurred, together with FKBP12.6 dissociation and Ca2+ leak.


CONCLUSIONS
The specific domain interaction within the RyR regulates the channel gating property, and the defectiveness in the mode of the interdomain interaction seems to be the initial critical step of the pathogenesis of heart failure.
Oda
Tetsuro
T
Department of Medical Bioregulation, Division of Cardiovascular Medicine, Yamaguchi University School of Medicine, Yamaguchi, Japan.
Yano
Masafumi
M
Yamamoto
Takeshi
T
Tokuhisa
Takahiro
T
Okuda
Shinichi
S
Doi
Masahiro
M
Ohkusa
Tomoko
T
Ikeda
Yasuhiro
Y
Kobayashi
Shigeki
S
Ikemoto
Noriaki
N
Matsuzaki
Masunori
M
D000818:Animals; D001665:Binding Sites; D002118:Calcium / Q000378:metabolism; D000242:Cyclic AMP / Q000378:metabolism; D004195:Disease Models, Animal; D004285:Dogs; D005456:Fluorescent Dyes; D006333:Heart Failure / Q000209:etiology*; D006352:Heart Ventricles / Q000166:cytology / Q000648:ultrastructure; D015640:Ion Channel Gating; D020125:Mutation, Missense; D032383:Myocytes, Cardiac / Q000166:cytology / Q000378:metabolism; D010766:Phosphorylation; D017434:Protein Structure, Tertiary; D019837:Ryanodine Receptor Calcium Release Channel / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D012519:Sarcoplasmic Reticulum / Q000737:chemistry; D017180:Tachycardia, Ventricular / Q000209:etiology; D022061:Tacrolimus Binding Protein 1A / Q000378:metabolism
D005456:Fluorescent Dyes; D019837:Ryanodine Receptor Calcium Release Channel; D000242:Cyclic AMP; D022061:Tacrolimus Binding Protein 1A; D002118:Calcium