Effects of PKA on cTnI phosphorylation and Ca²⁺ sensitivity in PP1-treated PLV. (A) Western blotting showing the effect of PP1 or PKA on the phosphorylation level of Ser23/24 in cTnI (12.5 µg protein/well). Cont., control with no treatment. Normalized intensity compared with control (n = 5): PP1, 40.16 ± 10.48%; PP1 + PKA (PKA phosphorylation after PP1 treatment), 207.76 ± 53.85% (P < 0.05 compared with PP1). (B) Force-pCa curves showing the effects of PP1 and subsequent PKA treatment on Ca²⁺ sensitivity. (Inset) Difference between the values of the PKA-induced shift of pCa₅₀ (C, control minus PP1 + PKA; PP1, PP1 minus PP1 + PKA). *, P < 0.05. n = 7. PKA treatment did not significantly affect maximal force or n_H (see Table II). (C; Left) Comparison of Ca²⁺ sensitization as indexed by the shift of pCa₅₀ after PP1 treatment and cTn or PCRF reconstitution in PLV. (Right) Comparison of the PKA-induced shift of pCa₅₀ in PP1-treated and cTn- or PCRF-reconstituted PLV. Statistical significance was not observed between groups in either graph.