Figure 8. Isolated skeletal muscle contractures induced by nanomolar dantrolene sodium (DS). (A) Human vastus lateralis from malignant hyperthermia susceptible (MHS) person. Twenty nanomoles DS added at arrow produced 1.3 g isometric contracture. (B) MHS dog gracilis produces phenotypic contracture response to halothane. Addition of 20 nM DS produces a 0.54-g contracture above the steady-state tension produced by halothane.