Table 3.

Dynamic Stretch‐Activation Parameters Measured Before and Following Myk461 Incubation in WT and KO Myocardium at pCa 6.1

Group	krel (s−1)	kdf (s−1)	P1	P2	P3	Pdf
WT
Pre‐Myk461	434.45±37.30	8.46±0.52	0.521±0.017	−0.050±0.013	0.144±0.008	0.194±0.012
0.5 μmol/L Myk461	442.91±35.82	5.53±0.55a	0.556±0.025	0.040±0.017a	0.223±0.013a	0.183±0.017
1.0 μmol/L Myk461	459.02±40.84	4.41±0.44a	0.597±0.030	0.123±0.022a	0.278±0.029a	0.156±0.019
KO
Pre‐Myk461	898.05±42.65b	12.31±0.85b	0.473±0.044	−0.057±0.014	0.217±0.012b	0.275±0.019b
0.5 μmol/L Myk461	576.77±57.39a	6.40±0.39a	0.590±0.022a	0.038±0.023a	0.233±0.009	0.195±0.016a
1.0 μmol/L Myk461	437.60±45.40a	5.25±0.35a	0.637±0.021a	0.139±0.014a	0.268±0.007a	0.129±0.012a

k_df, 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; XB, cross‐bridge. Stretch activation amplitudes were normalized to prestretch steady‐state Ca²⁺‐activated force, which refers to the activation level (≈40%–45% 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.

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

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