Abstract
The present study investigates the effects of the first mutation of troponin C (hcTnC(L29Q)) found in a patient with hypertrophic cardiomyopathy (HCM) on force-pCa relations and the interplay with phosphorylation of sarcomeric PKA substrates. In triton-skinned murine cardiac fibers, the endogenous mcTnC was extracted and the fibers were subsequently reconstituted with recombinant wild-type and mutant hcTnC. Force-pCa relations of preparations containing hcTnC(L29Q) or hcTnC(WT) were similar. Incubation of fibers reconstituted with the recombinant proteins with phosphatase to dephosphorylate sarcomeric PKA substrates induced an increase in Ca2+ sensitivity, slightly more pronounced (0.04 pCa units) in hcTnC(L29Q)-containing fibers. Incubation of the dephosphorylated fibers with PKA induced significant rightward shifts of force-pCa relations of similar magnitude with both, hcTnC(L29Q) and hcTnC(WT). No significant effects of hcTnC(L29Q) on the velocity of unloaded shortening were observed. In conclusion, no major differences in contractile parameters of preparations containing hcTnC(L29Q) compared to hcTnC(WT) were observed. Therefore, it appears unlikely that hcTnC(L29Q) induces the development of HCM by affecting the regulation of Ca2+-activated force and interference with PKA-mediated modulation of the Ca2+ sensitivity of contraction.