Abstract
1. 1. Parathion induces tonic contractures in crab skeletal muscle. These contractures are irreversible at concentrations greater than about 100 μM. 2. 2. The contracture-induction effect was examined in terms of disruption of the electromechanical coupling process at a number of possible stages, (a) membrane depolarization, (b) the reticular calcium control system, (c) actomyosin cross bridge formation and (d) structural changes in the fibres. 3. 3. It has been established that parathion does not activate muscle by a transient depolarization, but it does significantly depress reticular calcium uptake. In addition, parathion greatly modifies actomyosin superprecipitation, and fine-structural studies show great disruption of reticular organization, suggestive of massive calcium loss from the reticulum into the myoplasm.
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