Dantrolene inhibition of ryanodine receptor Ca2+ release channels -: Molecular mechanism and isoform selectivity

As an inhibitor of Ca2+ release through ryanodine receptor (RYR) channels, the skeletal muscle relaxant dantrolene has proven to be both a valuable experimental probe of intracellular Ca2+ signaling and a lifesaving treatment for the pharmacogenetic disorder malignant hyperthermia. However, the molecular basis and specificity of the actions of dantrolene on RYR channels have remained in question. Here we utilize [H-3]ryanodine binding to further investigate the actions of dantrolene on the three mammalian RME isoforms. The inhibition of the pig skeletal muscle RYR1 by dantrolene (10 muM) was associated with a 3-foId increase in the K-d of [H-3]ryanodine binding to sarcoplasmic reticulum (SR) vesicles such that dantrolene effectively reversed the 3-fold decrease in the K-d for [H-3]ryanodine binding resulting from the malignant hyperthermia RYR1 Arg(615) --> Cys mutation. Dantrolene inhibition of the RYR1 was dependent on the presence of the adenine nucleotide and calmodulin and reflected a selective decrease in the apparent affinity of RYR1 activation sites for Ca2+ relative to Mg2+. In contrast to the RYR1 isoform, the cardiac RYR2 isoform was unaffected by dantrolene, both in native cardiac SR vesicles and when heterologously expressed in HEK-293 cells. By comparison, the RYR3 isoform expressed in HEK-293 cells was significantly inhibited by dantrolene, and the extent of RYR3 inhibition was similar to that displayed by the RYR1 in native SR vesicles. Our results thus indicate that both the RYR1 and the RYR3, but not the RYR2, may be targets for dantrolene inhibition in vivo.