Determinates of Dantrolene Inhibition of Ryanodine Receptors

Dantrolene is a neutral hydantoin that is clinically used as a skeletal muscle relaxant to prevent RyR1 over activation in response to volatile anaesthetics. Previously we found that dantrolene produces up to a 45% inhibition of sheep RyR2 an IC50 of 100 nM and that this inhibition requires CaM. In this study, we examine the effect of dantrolene on human RyR2 that are isolated from healthy human donor hearts and hearts with ischaemic cardiomyopathy (ICM) with ethics approval (UoN H-2009-0369; Univ Sydney #2012/2814; QUT EC28114) and incorporated into lipid bilayers. We found that RyR2 from healthy human hearts were not inhibited by dantrolene at concentrations up to 10 μM whereas for RyR2 from human hearts with ICM, dantrolene caused a 40% reduction in open probability. Hyper-phosphorylating these RyR2 channels with PKA prior to experiments abolished the effect of dantrolene. The effect of dantrolene in sheep ryR2 was abolished by prior exposure of RyR2 to FK506, a compound known to dissociate FKBP12.6 from the RyR2 complex. This suggests that in addition to CaM, FKBP12.6 is necessary for dantrolene inhibition of RyR2.