Dantrolene is a drug that suppresses intracellular Ca
2+ release from sarcoplasmic reticulum in normal skeletal muscle and is used as a therapeutic agent in individuals susceptible to malignant hyperthermia. Though its precise mechanism of action has not been elucidated, we have identified the N-terminal region (amino acids 1-1400) of the skeletal muscle isoform of the ryanodine receptor (RyR1), the primary Ca a molecular target for dantrolene using the photoaffinity analog [RyR1 retains its capacity to be specifically labeled with [ indicating that muscle specific factors are not required for this ligand-receptor interaction. Synthetic domain peptides of RyR1, previously shown to affect RyR1 function and used in photoaffinity labeling experiments. Only DP1 and DP1-2, peptides containing the amino acid sequence corresponding to RyR1 residues 590-609 were specifically labeled by [antibody which recognizes RyR1 and its 1400 amino acid N-terminal fragment, recognizes DP1 and DP1-2 in both Western blots and immunoprecipitatio assays, and specifically inhibits [its N-terminal fragment in sarcoplasmic reticulum. Our results indicate that synthetic domain peptides can mimic a native, ligand binding conformation vitro antibody on RyR1 are equivalent and composed of amino-acids 590-609.