Interplay Between the Effects of Dilated Cardiomyopathy Mutation (R206L) and the Protein Kinase C Phosphomimic (T204E) of Rat Cardiac Troponin T Are Differently Modulated by α‐ and β‐Myosin Heavy Chain Isoforms

Background We hypothesized that the functional effects of R206L—a rat analog of the dilated cardiomyopathy ( DCM ) mutation R205L in human cardiac troponin T (TnT)—were differently modulated by myosin heavy chain ( MHC ) isoforms and T204E, a protein kinase C ( PKC ) phosphomimic of TnT. Our hypothesis was based on two observations: (1) α‐ and β‐ MHC differentially influence the functional effects of TnT; and (2) PKC isoforms capable of phosphorylating TnT are upregulated in failing human hearts. Methods and Results We generated 4 recombinant TnT variants: wild type; R206L; T204E; and R206L+T204E. Functional effects of the TnT variants were tested in cardiac muscle fibers (minimum 14 per group) from normal (α‐ MHC ) and propylthiouracil‐treated rats (β‐ MHC ) using steady‐state and dynamic contractile measurements. Notably, in α‐ MHC fibers, Ca 2+ ‐activated maximal tension was attenuated by R206L (≈32%), T204E (≈63%), and R206L+T204E (≈64%). In β‐ MHC fibers, maximal tension was unaffected by R206L, but was attenuated by T204E (≈33%) and R206L+T204E (≈40%). Thus, β‐ MHC differentially counteracted the attenuating effects of the TnT variants on tension. However, in β‐ MHC fibers, R206L+T204E attenuated tension to a greater extent when compared to T204E alone. In β‐ MHC fibers, R206L+T204E attenuated the magnitude of the length‐mediated recruitment of new cross‐bridges (≈28%), suggesting that the Frank‐Starling mechanism was impaired. Conclusions Our findings are the first (to our knowledge) to demonstrate that the functional effects of a DCM ‐linked TnT mutation are not only modulated by MHC isoforms, but also by the pathology‐associated post‐translational modifications of TnT.