Effect of troponin C on the cooperativity in Ca2+ activation of cardiac muscle.

This study describes the effects of exchanging native cardiac troponin C (CTnC) from the right ventricular muscle of Syrian hamster for purified skeletal (S) TnC from fast twitch muscles in triggering cardiac contraction. Ca2+ sensitivity of the myocardium became decreased with STnC to 62% of the original value with CTnC. Furthermore, the slope of the pCa-force curve of cardiac muscle was found to be increased with STnC. The results show that the TnC moiety, as part of the switching mechanism during activation, also regulates thin-filament cooperativity in muscle. Modifications in both the Ca2+ sensitivity and cooperativity are associated with alterations in the primary structure of TnC.