The origin of the instantaneous elasticity in single frog muscle fibres.

High-speed cinematographic recordings of single tetanized muscle fibres during a quick decrease in length revealed that the shortening was mostly localized at the fibre segment nearest the released end of the fibre, indicating that the instantaneous elasticity may not originate from the elasticity of the cross-bridges.     

Development of the maximum isometric force at short sarcomere lengths in calcium-activated muscle myofibrils

Summary Studies on the sarcomere length-force relation in Ca⁺⁺-activated vertebrate muscle myofibrils indicate that the maximum isometric force can be generated even at sarcomere lengths around 1 m, indicating that the ascending limb of the sarcomere length-force relation is virtually absent.We thank Miss S. Gomi for her technical assistance. This work was supported by the grant (No. 587028) form the Ministry of Education, Science and Culture of Japan.     

The origin of the instantaneous elasticity in single frog muscle fibres

Summary High-speed cinematographic recordings of single tetanized muscle fibres during a quick decrease in length revealed that the shortening was mostly localized at the fibre segment nearest the released end of the fibre, indicating that the instantaneous elasticity may not originate from the elasticity of the cross-bridges.We wish to thank Dr H. Hashizume of the Engineering Research Institute, Tokyo University for providing facilities to use the ultra high-speed cinecamera, and Mr T. Tsuno, Mr Y. Nakamura and Miss S. Gomi for their technical assistance.     

Calcium transients in a molluscan smooth muscle

Summary The changes in myoplasmic calcium concentration during contraction were recorded in the anterior byssal retractor muscle ofMytilus edulis using murexide as calcium indicator, and were found to be qualitatively similar to those in striated muscles except for their slow time course.     

The origin of the series elastic component in single crayfish muscle fibres.

High-speed cinematographic studies on the length changes of single tetanized crayfish muscle fibres during a step decrease in length revealed a farily uniform distribution of a highly compliant series elastic component along the fibre length, suggesting that it mainly originates from some structures in each sarcomere other than the cross-bridges.     

Changes in the A-band width during contraction in horseshoe crab striated muscle

Summary Cinematographic recordings of Ca-activated contraction in glycerinated bundles of myofibrils of the horseshoe crab striated muscle indicated that the A-band width did not change during rapid sarcomere shortening from 11 to 4 m, while it increased by about 10% in nearly isometric conditions.We wish to thank T. Taniguchi, M. Kusama and M. Goto for their excellent technical assistance in taking cinematographic recordings.     

The origin of the series elastic component in single crayfish muscle fibres

Summary High-speed cinematographic studies on the length changes of single tetanized crayfish muscle fibres during a step decrease in length revealed a fairly uniform distribution of a highly compliant series elastic component along the fibre length, suggesting that it mainly originates from some structures in each sarcomere other than the cross-bridges.We wish to thank Dr H. Hashizume of the Engineering Research Institute, Tokyo University for providing facilities to use the ultra high-speed cine-camera, and Mr T. Tsuno, Mr Y. Nakamura and Miss S. Gomi for their technical assistance.