Amphidinolide B, a powerful activator of actomyosin ATPase enhances skeletal muscle contraction

Amphidinolide B caused a concentration-dependent increase in the contractil e force of skeletal muscle skinned fibers. The concentration-contractile re sponse curve for external Ca2+ was shifted to the left in a parallel manner , suggesting an increase in Ca2+ sensitivity. Amphidinolide B stimulated th e superprecipitation of natural actomyosin. The maximum response of natural actomyosin to Ca2+ in superprecipitation was enhanced by it. Amphidinolide B increased the ATPase activity of myofibrils and natural actomyosin. The ATPase activity of actomyosin reconstituted from actin and myosin was enhan ced in a concentration-dependent manner in the presence or absence of tropo nin -tropomyosin complex, Ca2+-, K+-EDTA- or Mg2+-ATPase of myosin was not affected by amphidinolide B. These results suggest that amphidinolide B enh ances an interaction of actin and myosin directly and increases Ca2+ sensit ivity of the contractile apparatus mediated through troponin-tropomyosin sy stem? resulting in an increase in the ATPase activity of actomyosin and thu s enhances the contractile response of myofilament. (C) 1999 Elsevier Scien ce B.V. All rights reserved.