Contraction in a Muscle with Negligible Sarcoplasmic Reticulum: The Longitudinal Retractor of the Sea Cucumber lsostichopus badionotus (Selenka), Holothuria Aspidochirota
Hill R, Sanger J, Yantorno R, Deutsch C. 1978. Contraction in a Muscle with Negligible Sarcoplasmic Reticulum: The Longitudinal Retractor of the Sea Cucumber lsostichopus badionotus (Selenka), Holothuria Aspidochirota. Journal of Experimental Zoology. 206(2):137 - 150
The longitudinal retractor muscles of the body wall of the sea cucumber Isostichopus badionotus have small cells joined in small bundles by extensive areas of tight surface contact between the cells and on projections at the center of the bundles. The cells have only a few small mitochondria and negligible sarcoplasmic reticulum. It might be expected that such cells would be poor in intracellular storage sites for calcium for excitation-contraction coupling. However, we have found that it requires up to ten hours incubation of the isolated muscles in calcium-free solutions of chelating agents to abolish contractility in the calcium-free solutions. After that, contraction is directly calcium dependent. Contractility was assessed by measuring either force or shortening during potassium depolarization across a sucrose gap. Caffeine induces contraction even in calcium-free solutions. Thus the physiological evidence indicates that there are internal storage sites for calcium, even though there is scarcely any sarcoplasmic reticulum. On morphological grounds we suggest that there are also superficial sarcolemmic storage sites for calcium. This is suggested by the great increase in sarcolemmic area provided by extraordinary extensions of each cell into the lumen of the bundle.
- Type
- Journal Article
- Authors
- Hill, Robert; Sanger, Joseph; Yantorno, Robert; Deutsch, Carol
- Units
- SFCN
- Keywords
- Anatomy, Calcium dependence, Contractility, Movement, Physiology, stretch