Journal article
Identification of two new regions in the N-terminus of cardiac troponin T that have divergent effects on cardiac contractile function
The Journal of physiology, Vol.591(5), pp.1217-1234
03/01/2013
Handle:
https://hdl.handle.net/2376/100687
PMCID: PMC3607867
PMID: 23207592
Abstract
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 α-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 α- and β-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 (α-Tm) fibres. The desensitizing effect of McTnT1-44 on pCa50 was ablated in β-Tm fibres. McTnT45-74 enhanced pCa50 in both α- and β-Tm fibres, with β-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 β-Tm fibres. The magnitude of the length-mediated recruitment of XBs was attenuated by McTnT1-44 in β-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 α- and β-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.
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Details
- Title
- Identification of two new regions in the N-terminus of cardiac troponin T that have divergent effects on cardiac contractile function
- Creators
- Ranganath Mamidi - Department of Veterinary and Comparative Anatomy, Pharmacology and Physiology, Washington State University, Pullman, WA-99164, USA. murali@vetmed.wsu.eduSri Lakshmi MallampalliDavid F WieczorekMurali Chandra
- Publication Details
- The Journal of physiology, Vol.591(5), pp.1217-1234
- Academic Unit
- Integrative Physiology and Neuroscience, Department of
- Publisher
- England
- Grant note
- R01-HL-081680 / NHLBI NIH HHS R01 HL075643 / NHLBI NIH HHS R01-HL-075643 / NHLBI NIH HHS R01 HL081680 / NHLBI NIH HHS
- Identifiers
- 99900546561301842
- Language
- English
- Resource Type
- Journal article