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Journal of Experimental Biology 119,31-40 (1985)
Published by Company of Biologists 1985

The Maximum Shortening Velocity of Holothurian Muscle and Effects of Tonicity Change on it

T. TSUCHIYA ¹

¹ Bermuda Biological Station for Research, Ferry Reach 1-15, Bermuda; Department of Physiology, School of Medicine, Teikyo University, Itabashi-ku, Tokyo 173, Japan

1. 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.

2. At normal osmotic strength, the average maximum shortening velocity was 0.44 ± 0.04 L_oS^-1 (N=14) which is fast compared to other smooth muscles. This is unexpected considering the slow locomotion of these animals.

3. 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.

4. Lowering the osmotic strength by 19% or 39%, by reducing NaCl concentration, did not significantly affect shortening velocity.

5. The shortening velocity was found to be proportional to the volume of the muscle preparation.

Key words: Holothurian muscle, shortening velocity, tonicity change

Accepted on May 8, 1985