Contractile Properties of Holothurian Muscle.

The contractile properties of the radial muscle of a holothurian, Stichropus japonicas, were studied with the following results. (1) The muscle slowly contracts by the action of acetylcholine and KC1. The pattern of contracture is the same to both reagents. The muscle does not show caffeine-contracture. (2) Acetylcholine- and KCl-contractures are slowly relaxed after the removal of these reagents during the sustained or relaxing phases. The time course of relaxation resembles that observed under the existence of these reagents. (3) After quick release, the tension lowered is rapidly compensated during the early rising phase. No recovery of the tension is however detected when the quick release is performed during the sustained contracture phase. (4) The sustained contracture achieved in acetylcholine or KC1 is not released by serotonine and chlorobuthanol. (5) The pattern of contracture by acetylcholine is not changed in the muscle whose T-system is selectively disrupted.