Effects of dantrolene on the diaphragm muscle of the normal and myopathic hamster.

Dantrolene is the only known effective treatment for malignant hyperthermia. However, its effects on the myopathic diaphragm remain unknown. The effects of dantrolene 10(-8) to 10(-4) mol litre-1 on diaphragm muscle strips in normal (n = 12) and myopathic hamsters (n = 13) were investigated in vitro in response to tetanic stimulation. We studied contraction under isotonic and isometric conditions. Data are presented as mean (SD) percent of baseline. Dantrolene induced a negative inotropic effect in normal and myopathic hamsters but no significant difference was observed between groups (active force at 10(-4) mol litre-1; 34 (7) vs 32 (11)%; ns). We conclude that dantrolene induced a comparable negative inotropic effect on diaphragm muscle in normal and myopathic hamsters.