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Modulation of the rate of cardiac muscle contraction by troponin C constructs with various calcium binding affinities

Department of Physiology and Cell Biology, Ohio State University, Columbus, Ohio

Submitted 10 January 2007 ; accepted in final form 7 August 2007

We investigated whether changing thin filament Ca²⁺ sensitivity alters the rate of contraction, either during normal cross-bridge cycling or when cross-bridge cycling is increased by inorganic phosphate (P_i). We increased or decreased Ca²⁺ sensitivity of force production by incorporating into rat skinned cardiac trabeculae the troponin C (TnC) mutants V44QTnC^F27W and F20QTnC^F27W. The rate of isometric contraction was assessed as the rate of force redevelopment (k_tr) after a rapid release and restretch to the original length of the muscle. Both in the absence of added P_i and in the presence of 2.5 mM added P_i 1) Ca²⁺ sensitivity of k_tr was increased by V44QTnC^F27W and decreased by F20QTnC^F27W compared with control TnC^F27W; 2) k_tr at submaximal Ca²⁺ activation was significantly faster for V44QTnC^F27W and slower for F20QTnC^F27W compared with control TnC^F27W; 3) at maximum Ca²⁺ activation, k_tr values were similar for control TnC^F27W, V44QTnC^F27W, and F20QTnC^F27W; and 4) k_tr exhibited a linear dependence on force that was indistinguishable for all TnCs. In the presence of 2.5 mM P_i, k_tr was faster at all pCa values compared with the values for no added P_i for TnC^F27W, V44QTnC^F27W, and F20QTnC^F27W. This study suggests that TnC Ca²⁺ binding properties modulate the rate of cardiac muscle contraction at submaximal levels of Ca²⁺ activation. This result has physiological relevance considering that, on a beat-to-beat basis, the heart contracts at submaximal Ca²⁺ activation.

force; thin filament

This article has been cited by other articles:

				J. P. Davis and S. B. Tikunova Ca2+ exchange with troponin C and cardiac muscle dynamics Cardiovasc Res, March 1, 2008; 77(4): 619 - 626. [Abstract] [Full Text] [PDF]