Dantrolene sodium is an inhibitor of Ca²⁺ release from sarcoplasmic reticulum via inhibition of ryanodine receptor (RYR) channels. Displays selectivity for RYR1 and RYR3 over RYR2. Acts asa skeletal muscle relaxant that depresses excitation-contraction coupling in skeletal muscle by binding to the type 1 ryanodine receptor and decreasing free intracellular calcium concentration.