The R144W Mutation in Mouse Cardiac Troponin T Attenuates Crossbridge Recruitment and Detachment Kinetics

Abstract

Listen

Translate article

A missense mutation, R141W, in the strong tropomyosin-binding region of human cardiac troponin T (cTnT) is associated with dilated cardiomyopathy (DCM). Previous studies of steady-state contractile function suggest that DCM-related mutations in cTnT attenuate myofilament Ca2+ sensitivity. Steady-state observations by themselves may not be sufficient enough to provide a reliable link between different mutations and divergent cardiac phenotypes, especially at submaximal Ca2+ levels. It is now widely appreciated that dynamic relationships - rather than steady-state aspects of the force-pCa relationship - dominate in conditions under which cardiac muscle functions. To understand the effects of the R141W mutation on cardiac contractile dynamics, we created a mouse cTnT analog (McTnTR144W) of the human mutation, R141W. McTnTR144W and the wild-type McTnT were individually reconstituted into detergent-skinned mouse cardiac muscle fibers and dynamic contractile features were assessed at maximal (pCa 4.3) and submaximal (pCa 5.5) activations. McTnTR144W-reconstituted fibers revealed the following. The speed of crossbridge (XB) recruitment, b, decreased significantly at both pCa 4.3 and pCa 5.5; however, the magnitude of decrease was 2-fold greater at submaximal activation. The speed of XB detachment dynamics, c, also decreased and was 1.7-fold greater at submaximal activation. However, the XB strain-mediated effects on the recruitment of other XBs (γ) - mediated by allosteric/cooperative mechanisms operating within the thin filament - decreased to a similar extent at both Ca2+ activations. Novel findings from our study will be discussed in terms of the McTnTR144W-induced effects on the thin filament cooperativity and its associations with slower rates of XB recruitment and detachment kinetics at physiologically relevant Ca2+ concentrations.