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.     

Regulation of cross-bridge detachment by Ca ions at high ionic strength in molluscan catch muscle

Changes in the profile of equatorial intensities of X-ray diffraction from an intact, anterior byssal retractor muscle (ABRM) of Mytilus were examined at rest, during contracture brought about by acetylcholine (ACh) and a subsequent rigor-like contraction caused by raising the tonicity of the external solution, and after returning the tonicity to normal. The results suggest that the cross-bridges formed between thick and thin actin filaments during the ACh-contracture were maintained in the hypertonic solution and broken on decreasing the tonicity before the recovery of spacing of the actin filament lattice. A similar rigor-like contraction was induced in glycerinated ABRM by increasing salt concentration during active contraction. The rigor-like force declined rapidly when Ca++ concentration decreased. The results suggest that the detachment of the cross-bridge from the actin filament is regulated by Ca++ at high ionic strength in the ABRM.     

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.     

Regulation of cross-bridge detachment by Ca ions at high ionic strength in molluscan catch muscle

Summary Changes in the profile of equatorial intensities of X-ray diffraction from an intact, anterior byssal retractor muscle (ABRM) ofMytilus were examined at rest, during contracture brought about by acetylcholine (ACh) and a subsequent rigor-like contraction caused by raising the tonicity of the external solution, and after returning the tonicity to normal. The results suggest that the cross-bridges formed between thick and thin actin filaments during the ACh-contracture were maintained in the hypertonic solution and broken on decreasing the tonicity before the recovery of spacing of the actin filament lattice. A similar rigor-like contraction was induced in glycerinated ABRM by increasing salt concentration during active contraction. The rigor-like force declined rapidly when Ca⁺⁺ concentration decreased. The results suggest that the detachment of the cross-bridge from the actin filament is regulated by Ca⁺⁺ at high ionic strength in the ABRM.     

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.     

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.