Dantrolene, a therapeutic agent for malignant hyperthermia, markedly improves the function of failing cardiomyocytes by stabilizing interdomain interactions within the ryanodine receptor.
OBJECTIVE
We sought to investigate the effect of dantrolene, a drug generally used to treat malignant hyperthermia, on the Ca2+ release and cardiomyocyte function in failing hearts.


BACKGROUND
The N-terminal (N: 1-600) and central (C: 2000-2500) domains of the ryanodine receptor (RyR) harbor many mutations associated with malignant hyperthermia in skeletal muscle RyR (RyR1) and polymorphic ventricular tachycardia in cardiac RyR (RyR2). There is strong evidence that interdomain interaction between these regions plays an important role in the mechanism of channel regulation.


METHODS
Sarcoplasmic reticulum vesicles and cardiomyocytes were isolated from the left ventricular muscles of dogs (normal or rapid ventricular pacing for 4 weeks), for Ca2+ leak, transient, and spark assays. To assess the zipped or unzipped state of the interacting domains, the RyR was labeled fluorescently with methylcoumarin acetate in a site-directed manner. We used a quartz-crystal microbalance technique to identify the dantrolene binding site within the RyR2.


RESULTS
Dantrolene specifically bound to domain 601-620 in RyR2. In the sarcoplasmic reticulum isolated from pacing-induced failing dog hearts, the defective interdomain interaction (domain unzipping) had already occurred, causing spontaneous Ca2+ leak. Dantrolene suppressed both domain unzipping and the Ca2+ leak, demonstrating identical drug concentration-dependence (IC50 = 0.3 micromol/l). In failing cardiomyocytes, both diastolic Ca2+ sparks and delayed afterdepolarization were observed frequently, but 1 micromol/l dantrolene inhibited both events.


CONCLUSIONS
Dantrolene corrects defective interdomain interactions within RyR2 in failing hearts, inhibits spontaneous Ca2+ leak, and in turn improves cardiomyocyte function in failing hearts. Thus, dantrolene may have a potential to treat heart failure, specifically targeting the RyR2.
Kobayashi
Shigeki
S
Department of Medicine and Clinical Science, Division of Cardiology, Yamaguchi University Graduate School of Medicine, Ube, Yamaguchi, Japan.
Yano
Masafumi
M
Suetomi
Takeshi
T
Ono
Makoto
M
Tateishi
Hiroki
H
Mochizuki
Mamoru
M
Xu
Xiaojuan
X
Uchinoumi
Hitoshi
H
Okuda
Shinichi
S
Yamamoto
Takeshi
T
Koseki
Noritaka
N
Kyushiki
Hiroyuki
H
Ikemoto
Noriaki
N
Matsuzaki
Masunori
M
D000818:Animals; D002118:Calcium / Q000378:metabolism; D003620:Dantrolene / Q000627:therapeutic use*; D004195:Disease Models, Animal; D004285:Dogs; D006333:Heart Failure / Q000188:drug therapy* / Q000209:etiology / Q000503:physiopathology; D008305:Malignant Hyperthermia / Q000150:complications / Q000188:drug therapy* / Q000503:physiopathology; D008564:Membrane Potentials / Q000187:drug effects; D018613:Microscopy, Confocal; D009125:Muscle Relaxants, Central / Q000627:therapeutic use*; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism* / Q000473:pathology; D019837:Ryanodine Receptor Calcium Release Channel / Q000187:drug effects / Q000378:metabolism*; D016896:Treatment Outcome; D016278:Ventricular Function, Right / Q000187:drug effects* / Q000502:physiology
D009125:Muscle Relaxants, Central; D019837:Ryanodine Receptor Calcium Release Channel; D003620:Dantrolene; D002118:Calcium