ABSTRACT
The maximum shortening velocity of the longitudinal retractor muscle of the holothurian, Isostichopus badionotus, was measured using a ‘slack test’ in solutions of normal, increased and reduced osmotic strength.
At normal osmotic strength, the average maximum shortening velocity was 0·44 ± 0·04L0s−1(N = 14) which is fast compared to other smooth muscles. This is unexpected considering the slow locomotion of these animals.
Raising the osmotic strength by 55% by addition of sucrose reduced the shortening velocity by more than 50%. Raising the osmotic strength by 52% with NaCl caused a 35% reduction in shortening velocity.
Lowering the osmotic strength by 19% or 39%, by reducing NaCl concentration, did not significantly affect shortening velocity.
The shortening velocity was found to be proportional to the volume of the muscle preparation.
