Calcium entry blockers inhibit contractures induced by the molluscicide Frescon in Lymnaea stagnalis smooth and cross-striated muscles

The molluscicide Frescon induces irreversible contracture in smooth and cross-striated muscles of the freshwater snail Lymnaea stagnalis. This contracture can be inhibited or reversed by elevated Mg²⁺ and reduced Ca²⁺ concentrations, by the heavy metals Ni²⁺, Co²⁺, and Mn²⁺, by the rare earth La³⁺, and by the calcium channel blocker D-600. The removal of extracellular Ca²⁺ also prevents the expression of Frescon action. These results are consistent with the hypothesis that Frescon causes an increase in the Ca²⁺ permeability of the sarcolemma.