Effects of PKA treatment on the activation dependence of the rate of force redevelopment in WT, cTnI_Ala5, cMyBP-C^−/−, and cTnI_Ala5/cMyBP-C^−/− skinned myocardium. The apparent rate constant of force redevelopment (k_tr) after a rapid release–restretch protocol measured as a function of relative isometric steady-state force (P/P₀) in untreated (•; n = 8) and PKA-treated (○; n = 8) preparations. All values are means ± SEM.