title: Tension Recovery following Ramp-Shaped Release in High-Ca and Low-Ca Rigor Muscle Fibers: Evidence for the Dynamic State of AMADP Myosin Heads in the Absence of ATP.
abstract: During muscle contraction, myosin heads (M) bound to actin (A) perform power stroke associated with reaction, AMADPPi → AM + ADP + Pi. In this scheme, A • M is believed to be a high-affinity complex after removal of ATP. Biochemical studies on extracted protein samples show that, in the AM complex, actin-binding sites are located at both sides of junctional peptide between 50K and 20K segments of myosin heavy chain. Recently, we found that a monoclonal antibody (IgG) to the junctional peptide had no effect on both in vitro actin-myosin sliding and skinned muscle fiber contraction, though it covers the actin-binding sites on myosin. It follows from this that, during muscle contraction, myosin heads do not pass through the static rigor AM configuration, determined biochemically and electron microscopically using extracted protein samples. To study the nature of AM and AMADP myosin heads, actually existing in muscle, we examined mechanical responses to ramp-shaped releases (0.5% of Lo, complete in 5ms) in single skinned rabbit psoas muscle fibers in high-Ca (pCa, 4) and low-Ca (pCa, >9) rigor states. The fibers exhibited initial elastic tension drop and subsequent small but definite tension recovery to a steady level. The tension recovery was present over many minutes in high-Ca rigor fibers, while it tended to decrease quickly in low-Ca rigor fibers. EDTA (10mM, with MgCl2 removed) had no appreciable effect on the tension recovery in high-Ca rigor fibers, while it completely eliminated the tension recovery in low-Ca rigor fibers. These results suggest that the AMADP myosin heads in rigor muscle have long lifetimes and dynamic properties, which show up as the tension recovery following applied release. Possible AM linkage structure in muscle is discussed in connection with the X-ray diffraction pattern from contracting muscle, which is intermediate between resting and rigor muscles.
authors: Department of Physiology, School of Medicine, Teikyo University, Tokyo, Japan.
authors: Haruo
authors: H
authors: Sugi
authors: Department of Physiology, Jikei University School of Medicine, Tokyo, Japan.
authors: Maki
authors: M
authors: Yamaguchi
authors: Department of Physiology, Jikei University School of Medicine, Tokyo, Japan.
authors: Tetsuo
authors: T
authors: Ohno
authors: Department of Electronic Engineering, Shibaura Institute of Technology, Tokyo, Japan.
authors: Takakazu
authors: T
authors: Kobayashi
authors: Department of Integrated Sciences in Physics and Biology, College of Humanities and Science, Nihon University, Tokyo, Japan.
authors: Shigeru
authors: S
authors: Chaen
authors: Department of Physiology, Jikei University School of Medicine, Tokyo, Japan.
authors: Hiroshi
authors: H
authors: Okuyama
mesh_terms: D000244:Adenosine Diphosphate / Q000378:metabolism*; D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D001696:Biomechanical Phenomena; D002118:Calcium / Q000378:metabolism*; D004058:Diffusion; D008297:Male; D055595:Mechanical Phenomena; D018485:Muscle Fibers, Skeletal / Q000378:metabolism* / Q000502:physiology; D009218:Myosins / Q000378:metabolism*; D011817:Rabbits
chemical_list: D000244:Adenosine Diphosphate; D000255:Adenosine Triphosphate; D009218:Myosins; D002118:Calcium