The effects of sodium selenite on rat diaphragm muscle

The effects of sodium selenite on isolated rat diaphragm muscle were investigated. Sodium selenite (0.1-3.0 mM) caused a complete inhibition of twitch responses elicited by either direct or indirect stimulation and induced a muscle contracture. These effects were irreversible and linearly related to the concentration of selenite and were not preceded by membrane depolarization. The contracture induced by sodium selenite is decreased by 50% in Ca++-free Ringer's solution containing 2.0 mM EDTA and the latency of muscle rigor was significantly reduced. The actions of selenite appeared to be temperature-dependent. Neither caffeine (20 mM) nor isotonic KCl solution produced any additional contracture after the completion of selenite rigor. Cysteine, tetrodotoxin, procaine and lidocaine failed to alter selenite-induced contracture. These results suggest that selenite probably caused an irreversible alteration in the contractile system of the mammalian muscle.