Effect of PKA on Ca²⁺ sensitivity in cTn-reconstituted RP. (A) Typical chart recording showing force-pCa protocols. A fiber was treated with cTn, PKA, and sTn, in this order (see Terui et al., 2008 for exchange ratio of Tn subunits under the same condition; i.e., ∼50% with cTn reconstitution). Green arrows (blue arrows) indicate percentage of force at pCa 6.0 (pCa 5.75) compared with the maximum obtained at the end of each force-pCa protocol. (B) Force-pCa curves showing the effects of cTn reconstitution, PKA treatment, and sTn reconstitution on Ca²⁺ sensitivity in RP. Black solid line, control with no treatment; gray solid line, cTn reconstitution; red solid line, PKA treatment; black dashed line, sTn reconstitution. (Inset) Summary of pCa₅₀ values. *, P < 0.05 compared with control; #, P < 0.05 compared with cTn reconstitution; †, P < 0.05 compared with PKA. n = 9. (C) Force-pCa curves showing the effect of PKA on Ca²⁺ sensitivity in RP with no Tn reconstitution. (Inset) pCa₅₀ values before and after PKA treatment. Maximal force: 175.35 ± 6.32 and 176.25 ± 5.31 mN/mm² (P > 0.05) before and after PKA, respectively; n_H: 4.61 ± 0.34 and 4.67 ± 0.30 (P > 0.05) before and after PKA, respectively. n = 7.