Table 4.

Dynamic Stretch‐Activation Parameters Measured Before and Following Myk461 Incubation in WT and KO Myocardium at pCa 6.0

Group	krel (s−1)	kdf (s−1)	P1	P2	P3	Pdf
WT
Pre‐Myk461	376.37±27.86	11.54±0.51	0.541±0.019	−0.017±0.010	0.130±0.009	0.149±0.012
0.5 μmol/L Myk461	410.39±32.74	7.43±0.58a	0.551±0.023	0.014±0.010	0.184±0.014a	0.171±0.016
1.0 μmol/L Myk461	424.23±42.04	6.00±0.84a	0.567±0.021	0.050±0.010a	0.217±0.012a	0.167±0.016
KO
Pre‐Myk461	792.67±53.56b	18.37±1.22b	0.526±0.021	−0.028±0.016	0.178±0.008b	0.206±0.013
0.5 μmol/L Myk461	578.47±65.90a,b	9.00±0.42a	0.573±0.021	0.021±0.024	0.209±0.010	0.189±0.018
1.0 μmol/L Myk461	513.60±52.89a	8.14±0.49a	0.611±0.019	0.062±0.023a	0.235±0.010a	0.173±0.017

Stretch activation amplitudes were normalized to prestretch steady‐state Ca²⁺‐activated force, which refers to the activation level (≈52%–57% of maximal Ca²⁺‐activated force) as described in the Methods section. Values are expressed as mean±SE of mean. Twelve skinned myocardial preparations (3 fibers each from 4 hearts) were used for both groups. Linear mixed model was used for data analysis with Tukey post hoc tests for multiple comparisons between groups of data. k_df indicates rate of XB recruitment; k_rel, rate of XB detachment; KO, knockout; P1, XB stiffness; P2, magnitude of XB detachment; P3, the new steady‐state force attained following a 2% stretch in muscle length; P_df, magnitude of XB recruitment; WT, wild‐type.

^aSignificantly different vs the corresponding pre‐Myk461 group (P<0.05).

^bSignificantly different vs the corresponding WT group (P<0.05).