Fig. 4.

Phosphorylation of sarcomeric proteins in pediatric cardiomyocytes. A: Pro-Q Diamond stain of nonfailing (NF) and dilated cardiomyopathy (DCM) samples. PKA, protein kinase A. B: myosin binding protein C (MBPC) phosphorylation [normalized to myosin essential light chain (MLC)1] is decreased in DCM (P = 0.0031) and increases with in vitro PKA treatment (P = 0.0495). Decreased MBPC phosphorylation correlates with increased calcium sensitivity (higher pCa₅₀), R² = 0.4415, P = 0.0361. C: troponin (Tn)I phosphorylation is decreased in DCM (P = 0.0252) and increases with in vitro PKA treatment (P = 0.0019). Decreased TnI phosphorylation correlates with increased calcium sensitivity, R² = 0.5185, P = 0.0188. D: desmin phosphorylation is increased in DCM (P = 0.0029) and does not change significantly with PKA treatment. No significant correlation is demonstrated between desmin phosphorylation and calcium sensitivity. E: tropomyosin (Tm) phosphorylation is not significantly altered in DCM but is increased with PKA treatment of DCM cardiomyocytes (P = 0.039). No significant correlation is demonstrated between Tm phosphorylation and calcium sensitivity. F: TnT phosphorylation is decreased in DCM (P = 0.0254), and there is a trend toward increased phosphorylation with PKA treatment (P = 0.1060). Decreased TnT phosphorylation is correlated with increased calcium sensitivity, R² = 0.4264, P = 0.0406. G: MLC2 phosphorylation is unchanged in DCM and does not change significantly with PKA treatment. No significant correlation is demonstrated between MLC2 phosphorylation and calcium sensitivity. NF: no. of subjects (N) = 6; NF+PKA: N = 6; DCM: N = 4; DCM+PKA: N = 4.