Hypertrophic cardiomyopathy mutation in cardiac troponin T (R95H) attenuates length-dependent activation in guinea pig cardiac muscle fibers

摘要

The central region of cardiac troponin T (TnT) is important for modulating the dynamics of muscle length-mediated cross-bridge recruitment. Therefore, hypertrophic cardiomyopathy mutations in the central region may affect cross-bridge recruitment dynamics to alter myofilament Ca~(2+) sensitivity and length-dependent activation of cardiac myofilaments. Given the importance of the central region of TnT for cardiac contractile dynamics, we studied if hypertrophic cardiomyopathy-linked mutation (TnTR94H)-induced effects on contractile function would be differently modulated by sarcomere length (SL). Recombinant wild-type TnT (TnTWT) and the guinea pig analog of the human R94H mutation (TnTR95H) were reconstituted into detergent-skinned cardiac muscle fibers from guinea pigs. Steady-state and dynamic contractile measurements were made at short and long SLs (1.9 and 2.3 μm, respectively). Our results demonstrated that TnTR95H increased pCaso (—log of free Ca~(2+) concentration) to a greater extent at short SL; TnT_R95H increased pCa_(50) by 0.11 pCa units at short SL and 0.07 pCa units at long SL. The increase in pCa_(50) associated with an increase in SL from 1.9 to 2.3 μm (△pCa_(50)) was attenuated nearly twofold in TnT_R95H fibers; △pCa_(50) was 0.09 pCa units for TnTwr fibers but only 0.05 pCa units for TnTR95H fibers. The SL dependency of rate constants of cross-bridge distortion dynamics and tension redevelopment was also blunted by TnTu95H. Collectively, our observations on the SL dependency of pCa_(50) and rate constants of cross-bridge distortion dynamics and tension redevelopment suggest that mechanisms underlying the length-dependent activation cardiac myofilaments are attenuated by TnTR95H.