Spontaneous oscillatory contraction (SPOC) of sarcomeres in skeletal muscle.

Skeletal myofibrils spontaneously oscillate under a condition where ATP, ADP, and Pi coexist and the concentration of free Ca2+ is less than about 1 microM. Although this oscillation phenomenon called SPOC is apparently simple, the molecular mechanism seems to be complex. The SPOC condition and the space-time pattern of SPOC wave suggest that the dynamics of association and dissociation of Pi (ADP) is regulated by the mechanical strain imposed on actin and myosin; the enzymatic activity (ATPase) of actomyosin complex and the mechanical event (contraction) are thus coupled to each other. In this sense, the nature of the mechanochemical enzyme, actomyosin ATPase, is revealed in SPOC.