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

Abstract

Amphidinolide B caused a concentration-dependent increase in the contractile force of skeletal muscle skinned fibers. The concentration–contractile response curve for external Ca 2+ was shifted to the left in a parallel manner, suggesting an increase in Ca 2+ sensitivity. Amphidinolide B stimulated the superprecipitation of natural actomyosin. The maximum response of natural actomyosin to Ca 2+ 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 enhanced in a concentration-dependent manner in the presence or absence of troponin–tropomyosin complex. Ca 2+-, K +-EDTA- or Mg 2+-ATPase of myosin was not affected by amphidinolide B. These results suggest that amphidinolide B enhances an interaction of actin and myosin directly and increases Ca 2+ sensitivity of the contractile apparatus mediated through troponin–tropomyosin system, resulting in an increase in the ATPase activity of actomyosin and thus enhances the contractile response of myofilament.