Dantrolene Inhibition of Sarcoplasmic Reticulum Ca2+Release by Direct and Specific Action at Skeletal Muscle Ryanodine Receptors

Abstract

The skeletal muscle relaxant dantrolene inhibits the release of Ca 2؉ from the sarcoplasmic reticulum during excitation-contraction coupling and suppresses the uncontrolled Ca 2؉ release that underlies the skeletal muscle pharmacogenetic disorder malignant hyperthermia; however, the molecular mechanism by which dantrolene selectively affects skeletal muscle Ca 2؉ regulation remains to be defined. Here we provide evidence of a high-affinity, monophasic inhibition by dantrolene of ryanodine receptor Ca 2؉ channel function in isolated sarcoplasmic reticulum vesicles prepared from malignant hyperthermia-susceptible and normal pig skeletal muscle. In media simulating resting myoplasm, dantrolene increased the half-time for 45 Ca 2؉ release from both malignant hyperthermia and normal vesicles approximately 3. The muscle relaxant dantrolene is a potent and specific inhibitor of skeletal muscle excitation-contraction (E-C) 1 coupling (1). Dantrolene (ϳ10 M) reduces skeletal muscle twitch force by approximately 75% (2) and shifts the sensitivity of contractile activation to higher voltages (3, 4), these effects being attributed to a partial block by dantrolene of Ca 2ϩ release from the sarcoplasmic reticulum (SR) (1,5,6). In contrast to these pronounced effects on skeletal muscle, effects of dantrolene on cardiac muscle contractility are mild or absent (1, 5, 7). Clinically, dantrolene has proven effective in the treatment of malignant hyperthermia (MH), a potentially fatal genetic disorder of skeletal muscle E-C coupling in which exposure to volatile anesthetics triggers uncontrolled SR Ca 2ϩ release, muscle contracture, and accelerated metabolism (8).The molecular basis of the action of dantrolene remains undefined but is generally presumed to involve either direct or indirect inhibitory effects on ryanodine receptor (RYR) Ca 2ϩ channels. To date, three RYR isoforms have been identified in mammalian tissues and are termed RYR1, RYR2, and RYR3 (9). In skeletal muscle, the RYR1 isoform is the major pathway for SR Ca 2ϩ release during E-C coupling, and defects in these channels have been linked to MH susceptibility in pigs and in certain human families (8, 10). Moreover, recent evidence indicates that high-affinity [3 H]dantrolene and [ 3 H]ryanodine binding sites are localized to the same or closely associated skeletal muscle SR membrane fractions (11, 12). RYR1 channels thus constitute a likely target for the physiologic and therapeutic actions of dantrolene on skeletal muscle Ca 2ϩ regulation. Nonetheless, the precise mechanism by which dantrolene may affect the activation of RYR1 channels has remained unclear. In particular, it is not yet clear how dantrolene may alter RYR1 activation by the physiologic effectors of these channels that have been identified in studies using isolated SR vesicles preparations (13). In addition, whether the effects of dantrolene may reflect a direct interaction with the RYR1 channel complex itself or rather require dantrolene binding to a separate and as yet unidentified regulatory molecu...

Dantrolene Stabilizes Domain Interactions within the Ryanodine Receptor

“…In agreement with previous reports (7,12,13,45,46), we found that the extent of dantrolene inhibition of DP4-induced RyR1 channel activation, as determined by both [ 3 H]ryanodine binding and SR Ca 2ϩ release, varies with the temperature, i.e. significant inhibition was observed at 37°C, with only negligible inhibition at 22°C.…”

“…CaM alone (1 M) increased the specific activity of [ 3 H]ryanodine binding to the SR at 22°C, but dantrolene was now able to significantly suppress radioligand binding (ϳ35%) (Table II). When we carried out the same type of experiments at 37°C, dantrolene produced equivalently significant inhibition of [ 3 H]ryanodine binding (ϳ59%) in the presence or absence of CaM, in agreement with previous reports (7,12,13,45). These results suggest that higher temperature and CaM have similar effects on the extent of dantrolene inhibition of DP4-induced activation of RyR Ca 2ϩ channels.…”

“…It has been shown that both dantrolene and its equipotent, watersoluble analog azumolene suppress SR Ca 2ϩ release induced by Ca 2ϩ and various pharmacological agents (3, 10 -12). Although dantrolene has been shown to suppress the ryanodine binding activity of the SR (13,14), this finding is not universal (15). Dantrolene (1-5 M) has been reported to have a biphasic effect on the open probability of RyR1 channels in lipid bilayers, first activating and then blocking at nanomolar concentrations (16), but others have not been able to see any effect of this drug on single channels (3).…”

“…According to an earlier report (13), the addition of CaM is required to observe dantrolene inhibition of RyR1 channel function. We addressed the question of the possible role of CaM in modulating dantrolene activity in this study.…”

Carbamazepine toxicity following Oxybutynin and Dantrolene administration: a case report

“…6 Dantrolene relaxes striated muscles by inhibiting the release of Ca 2 þ from the sarcoplasmic reticulum. 7 The drug commonly causes transient drowsiness, weakness, general malaise, fatigue, diarrhea, and liver test dysfunction that requires strict laboratory follow-up. 8 The potential liver toxicity discourages some physicians from using Dantrolene, but still many use it for long periods.…”