ELEVATED MYOPLASMIC CALCIUM IN EXERCISE-INDUCED EQUINE RHABDOMYOLYSIS

Exertional rhabdomyolysis is a myopathy of unknown pathophysiology, We measured intracellular resting calcium concentration ([Ca2+](i)) by m eans of Ca2+-selective microelectrodes in intercostal muscle fibers fr om horses suffering from rhabdomyolysis, and from horses with no evide nce of neuromuscular disorder. [Ca2+](i) was several-fold higher in mu scle fibers from horses suffering from rhabdomyolysis when compared to controls. Treatment of rhabdomyolytic horses with dantrolene, an agen t that prevents Ca2+ release from the sarcoplasmic reticulum, reduced [Ca2+](i) toward control values, and accelerated the recovery from thi s myopathy, These results indicate that an acute episode of rhabdomyol ysis is associated with elevation in [Ca2+](i) in skeletal muscles, an d that dantrolene might be of benefit in treating this disease.