Effects of PKA on cTnI phosphorylation and Ca²⁺ sensitivity in PLV. (A; Top) Western blotting showing cTnI phosphorylation (12.5 µg protein/well). Cont., control without PKA treatment. (Bottom) Comparison of the intensity of cTnI Ser23/24 phosphorylation normalized with total cTnI content in control and PKA-treated PLV. *, P < 0.05. n = 3. (B) Force-pCa curves showing the effect of PKA on Ca²⁺ sensitivity. (Inset) pCa₅₀ values before and after PKA treatment. *, P < 0.05. n = 7. (C) Force-pCa curves showing the effects of quasi-complete sTn reconstitution (shown in gray) and subsequent treatment with PKA on Ca²⁺ sensitivity. (Inset) pCa₅₀ values. *, P < 0.05. n = 7. (D; Left) Plot of sTn treatment time versus sTn-induced shift of pCa₅₀. (Middle) Plot of sTn treatment time versus PKA-induced shift of pCa₅₀. (Right) Plot of residual cTnI ratio (i.e., cTnI/(cTnI + sTnI)) versus PKA-induced shift of pCa₅₀. n = 7.