BPS2026 – PKA phosphorylation of cTnI increases power output in non-phosphorylatable cMyBP-C permeabilized cardiac myocytes

Our lab studies regulation of myofilament power output. We previously reported PKA increased power output in permeabilized rat cardiac myocytes (Herron et. al., Circ Res . 2001). Since PKA phosphorylates multiple myofilament proteins including cardiac Myosin Binding Protein-C (cMyBP-C) and cardiac troponin I (cTnI), the molecular specificity remains uncertain. We investigated the molecular specificity of PKA regulation of power output by using a non-phosphorylatable cMyBP-C mouse model (cMyBP-C 3tSA). We tested the hypothesis that cTnI phosphorylation could augment power in non-phosphorylatable cMyBP-C myofilaments. We prepared permeabilized cardiac myocytes from cMyBP-C t3SA mice and confirmed that PKA treatment did not phosphorylate cMyBP-C but increased cTnI phosphorylation by western blot analysis. Next, cMyBP-C t3SA permeabilized cardiac myocyte preparations were attached between a force transducer and motor to measure contractile properties before and after PKA. Cardiac myocyte preparations ( n = 5) averaged 139 ± 9 μm in length and 25 ± 2 μm in width. After PKA, there was a tendency for greater maximum Ca 2+ -activated tension (before PKA 35 ± 5 kN·m −2 ; after PKA 39 ± 6 kN·m −2 , p = 0.235) but no change in maximum Ca 2+ -activated k tr (before PKA 15.6 ± 3 s −1 ; after PKA 15.4 ± 2 s −1 , p = 0.934 via paired t test). Following PKA, force-velocity curves and power-load relationships were shifted upward during ∼half-maximal Ca 2+ activations. After PKA, peak normalized power output (PNPO) was significantly increased (before PKA 0.237 ± 0.03; after PKA 0.310 ± 0.04 P/P 0 ·ML·s −1 , p = 0.009). We conclude that PKA can increase power in absence of cMyBP-C phosphorylation, suggesting a significant role of cTnI phosphorylation. This has implications for targeting thin filament proteins to augment cardiac reserve, especially in situations of reduced cMyBP-C phosphorylation, which is a signature in heart failure.