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.
Tameyasu
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Department of Physiology, Teikyo University School of Medicine, Tokyo, Japan.
D000109:Acetylcholine / Q000494:pharmacology; D000205:Actomyosin / Q000648:ultrastructure; D000818:Animals; D049872:Bivalvia / Q000502:physiology*; D002118:Calcium / Q000502:physiology*; D008974:Mollusca / Q000502:physiology*; D009119:Muscle Contraction; D009126:Muscle Relaxation; D009132:Muscles / Q000502:physiology* / Q000648:ultrastructure; D011188:Potassium / Q000502:physiology; D014961:X-Ray Diffraction
D000205:Actomyosin; D000109:Acetylcholine; D011188:Potassium; D002118:Calcium