The discovery of troponin (Ebashi and Kodama, 1965; cf. Ebashi et al., 1969) established the concept of regulation in muscle contraction and the term regulatory proteins (Maruyama and Ebashi, 1970). The absence of troponin or other specific regulatory proteins in molluscan striated muscle (Kendrick-Jones et al., 1970) suggested that the mode of regulation by Ca2 + is not as simple as it was expected to be. The complexity of Ca2 + regulation was further confirmed by research on regulatory mechanisms in smooth muscle (cf. Ebashi, 1979).