ROLE OF TROPONIN-C IN DETERMINING THE CA-2-SENSITIVITY AND COOPERATIVITY OF THE TENSION DEVELOPMENT IN RABBIT SKELETAL AND CARDIAC MUSCLES()

The role of troponin C in determining the characteristic differences i n contraction between fast-twitch skeletal and cardiac muscles was inv estigated with rabbit skinned psoas fibers and left ventricular trabec ulae by exchanging their troponins C using a technique involving extra ction and replacement. In both muscle types, skeletal troponin C confe rred higher cooperativity on the Ca2+-activated tension development th an cardiac troponin C, indicating that troponin C plays a crucial role in determining the cooperativity in Ca2+ activation of vertebrate str iated muscle. Furthermore, the foreign type of troponin C was found to confer lower Ca2+ sensitivity on the tension development in both fast -twitch skeletal and cardiac muscles than the native type of troponin C. This indicates that the Ca2+ sensitivity of each muscle type is det ermined by troponin C interactions with other troponin subunits and no t by troponin C alone.