2001 Fiscal Year Final Research Report Summary
Morphological and ultrastructural changes of the membrane systems involved in excitation-contraction coupling in skeletal muscle during contraction
| Project/Area Number |
11558003
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| Research Category |
Grant-in-Aid for Scientific Research (B)
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| Allocation Type | Single-year Grants |
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| Section | 展開研究 |
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| Research Field |
体育学
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| Research Institution | National Institute of Fitness and Sports in Kanoya |
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Principal Investigator |
TAKEKURA Hiroaki National Institute of Fitness and Sports in Kanoya, Physiological Sciences, Professor, 体育学部, 教授 (00206963)
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| Co-Investigator(Kenkyū-buntansha) |
KASUGA Norikatsu Aichi University of Education, Phisical Education, Professor, 教育学部, 教授 (60152659)
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| Project Period (FY) |
1999 – 2001
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| Keywords | skeletal muscle / excitation-contraction coupling / sarcoplasmic reticulum / transverse tubules / exercise / triad / three-dimensional structure / electron microscope |
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| Research Abstract |
During excitation-contraction (e-c) coupling in skeletal muscle, depolarization of the surface membrane/transverse (T) tubule is converted into Ca^<2+> release from internal store, sarcoplasmic reticulum (SR). These two membrane systems make junctions with each other, named peripheral coupling, dyads, and triads or, collectively, calcium release units. Functional interaction between T tubule and SR involves two Ca^<2+> channels in these membrane complex: dihydropyridine receptors (DHPR) of surface membrane/transverse tubules, and ryanodine receptor (RyR) of SR. The steps leading to the differentiation of the specialized SR domain involved in CRUs are just beginning to be understood. Key to the formation of CRUs is a docking step, which allows the formation and stabilization of the SR-T tubule link. Candidates for the docking protein have been proposed. Another step is the insertion of RyRs and DHPRs within CRUs. The former can be followed using electron microscopy, since the cytoplasmic domains of RyRs are seen as well defined electron dense structures within the junctional gap between SR and plasmalemma/T tubules. Using the mouse diaphragm as a model, we report further insights into the morphogenesis of the membrane systems. We found that the SR-T docking and the trapping of RyRs at the junctions are two sequential steps in the formation of CRUs. A second, somewhat unexpected, finding is that the specific positioning of CRUs relative to the bands of the myofibrils proceeds positioning of the entire T tubule network in transverse planes associated with the myofibrils. We found that the SR-T docking and the trapping of RyRs at the junctions are two sequential steps in the formation of GRUs. These sequential stages suggest an order of inductive processes for the molecular differentiation and structural organization of the CRUs in skeletal muscle development.
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