Regulatory roles of MgADP and calcium in tension development of skinned cardiac muscle

Norio Fukuda, Hideaki Fujita, Takashi Fujita, Shin'ichi Ishiwata*

*Corresponding author for this work

    Research output: Contribution to journalArticlepeer-review

    42 Citations (Scopus)


    We investigated the regulatory roles of MgADP and free Ca2+ in isometric tension development in skinned bovine cardiac muscle. We found that, in the relaxed state without free Ca2+, MgADP elicited a sigmoidal increase in active tension, as is the case in skeletal muscle (ADP-contraction). The critical MgADP concentration, at which the tension increment became half-maximal, increased in proportion to MgATP concentration, with a slope of approximately 1 for cardiac and 4 for skeletal muscle. Raising the free Ca2+ concentration decreased the critical MgADP concentration in proportion to the free Ca2+ concentration. In addition, the apparent Ca2+ sensitivity of tension development increased with MgADP, while decreasing with inorganic phosphate (Pi); MgADP suppressed the Ca2+-desensitizing effect of Pi in a concentration-dependent manner. These activating effects of MgADP were quantitatively assessed by means of a model based upon the kinetic scheme of actomyosin ATPase. These experimental results and model simulation suggest that the state of thin filaments is synergistically regulated by both the binding of Ca2+ to troponin and the formation of the actomyosin-ADP complex.

    Original languageEnglish
    Pages (from-to)909-921
    Number of pages13
    JournalJournal of Muscle Research and Cell Motility
    Issue number8
    Publication statusPublished - 1998

    ASJC Scopus subject areas

    • Physiology
    • Clinical Biochemistry
    • Endocrinology
    • Cell Biology


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