| First Author | Mamidi R | Year | 2013 |
| Journal | J Physiol | Volume | 591 |
| Issue | 5 | Pages | 1217-34 |
| PubMed ID | 23207592 | Mgi Jnum | J:207956 |
| Mgi Id | MGI:5559980 | Doi | 10.1113/jphysiol.2012.243394 |
| Citation | Mamidi R, et al. (2013) Identification of two new regions in the N-terminus of cardiac troponin T that have divergent effects on cardiac contractile function. J Physiol 591(Pt 5):1217-34 |
| abstractText | Abstract Cardiac troponin T (cTnT) has a highly acidic extended N-terminus, the physiological role of which remains poorly understood. To decipher the physiological role of this unique region, we deleted specific regions within the N-terminus of mouse cTnT (McTnT) to create McTnT1-44 and McTnT45-74 proteins. Contractile function and dynamic force-length measurements were made after reconstituting the McTnT deletion proteins into detergent-skinned cardiac papillary fibres harvested from non-transgenic mice that expressed alpha-tropomyosin (Tm). To further understand how the functional effects of the N-terminus of cTnT are modulated by Tm isoforms, McTnT deletion proteins were reconstituted into detergent-skinned cardiac papillary fibres harvested from transgenic mice that expressed both alpha- and beta-Tm. McTnT1-44, but not McTnT45-74, attenuated maximal activation of the thin filament. Myofilament Ca(2+) sensitivity, as measured by pCa50 (-log of [Ca(2+)]free required for half-maximal activation), decreased in McTnT1-44 (alpha-Tm) fibres. The desensitizing effect of McTnT1-44 on pCa50 was ablated in beta-Tm fibres. McTnT45-74 enhanced pCa50 in both alpha- and beta-Tm fibres, with beta-Tm having a bigger effect. The Hill coefficient of tension development was significantly attenuated by McTnT45-74, suggesting an effect on thin-filament cooperativity. The rate of cross-bridge (XB) detachment and the strained XB-mediated impact on other XBs were augmented by McTnT1-44 in beta-Tm fibres. The magnitude of the length-mediated recruitment of XBs was attenuated by McTnT1-44 in beta-Tm fibres. Our data demonstrate that the 1-44 region of McTnT is essential for maximal activation, whereas the cardiac-specific 45-74 region of McTnT is essential for augmenting cooperativity. Moreover, our data show that alpha- and beta-Tm isoforms have divergent effects on McTnT deletion mutant's ability to modulate cardiac thin-filament activation and Ca(2+) sensitivity. Our results not only provide the first explicit evidence for the existence of two distinct functional regions within the N-terminus of cTnT, but also offer mechanistic insights into the divergent physiological roles of these regions in mediating cardiac contractile activation. |
