Fig. 5.

Reduced maximal isometric force, calcium sensitivity of steady-state muscle activation, and sinusoidal stiffness in fast-twitch fiber of C2^−/− EDL skinned fibers. (A) Force–pCa curve of skinned single EDL fiber in pCa 9.0 to 4.5 at 2.3 µm sarcomere length. (B) Increased steady-state isometric force generation after 3% dextran treatment in both WT and C2^−/− muscle fiber. (C) Maximum isometric force at pCa 4.5 with or without dextran treatment. The increase of isometric maximal force in C2^−/− fiber in dextran versus nondextran was 12% higher than that of WT in dextran versus nondextran. (D) Significantly decreased myofilament calcium sensitivity of contraction (pCa₅₀) in C2^−/− fiber with and without dextran treatment. (E) k_TR in submaximum calcium concentrations (pCa 5.5 and 5.4) increased in C2^−/−(n = 6 in each group) and (F) reduced sinusoidal stiffness of C2^−/− fiber in all calcium concentrations (pCa 9.0 to 4.5). (G) Maximum sinusoidal stiffness at pCa 4.5 increased more in C2^−/− (+62%) compared to WT (+22%) after dextran (3%) treatment (WT, n = 5 to 6 and C2^−/−, n = 6). (H) Complete deletion of fMyBP-C protein has no effect on sinusoidal stiffness during rigor in EDL muscle. (A–F) WT, n = 6; WT + Dex, n = 8; C2^−/−, n = 6; and C2^−/− + Dex, n = 7. (H) WT, n = 5; WT + Dex, n = 6; C2^−/−, n = 6; and C2^−/− + Dex, n = 6. Error bars represent ± SEM, *P < 0.05, **P < 0.01, and ***P < 0.001. NS, nonsignificant. Statistical analyses were performed in WT and C2^−/− by unpaired Student’s t test in each condition.