Effects of sulphydryl inhibitors on frog sartorius muscle: N‐ethylmaleimide

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Abstract
1 . The characteristic action of the –SH inhibitor, N-ethylmaleimide (NEM), is muscle rigour. The dose-response curve indicates a biphasic effect with maximum rigour tension produced by 10 mm NEM; beyond 1.0 mm there was an inverse relationship between dose and response. 2 . NEM produces a membrane depolarization unrelated to rigour development. 3 . NEM causes a sustained increase in 45Ca efflux from whole muscle. Pretreatment of a muscle with ethylenediamine tetra-acetic acid (EDTA, 5 mm) to remove membrane calcium does not alter the NEM induced 45Ca efflux. 4 . It is suggested that the primary site of NEM action is inhibition of calcium uptake by the sarcoplasmic reticulum thereby producing rigour. At concentrations above 1.0 mm, NEM may affect the myofilaments.

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