Fig. 1. Diagram of experimental arrangement. The byssal end of the preparation was hooked to the lower lever of the displacement transducer with a stainless steal wire connector, while the shell end was held with the extension of the force transducer. The lever was initially fixed in position by stops 1 and 2, and after the full development of ACh-induced isometric force, stop 2 was removed to load the preparation with the spring, hooked between the upper lever and the micromanipulator.