An internal domain of β-tropomyosin increases myofilament Ca 2+ sensitivity

Ganapathy Jagatheesan, Sudarsan Rajan, Emily M. Schulz, Rafeeq P.H. Ahmed, Natalia Petrashevskaya, Arnold Schwartz, Greg P. Boivin, Grace M. Arteaga, Tao Wang, Yi Gang Wang, Muhammad Ashraf, Stephen B. Liggett, John Lorenz, R. John Solaro, David F. Wieczorek

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10 Scopus citations


Tropomyosin (TM) is involved in Ca2+-mediated muscle contraction and relaxation in the heart. Striated muscle α-TM is the major isoform expressed in the heart. The expression of striated muscle β-TM in the murine myocardium results in a decreased rate of relaxation and increased myofilament Ca2+ sensitivity. Replacing the carboxyl terminus (amino acids 258-284) of α-TM with β-TM (a troponin T-binding region) results in decreased rates of contraction and relaxation in the heart and decreased myofilament Ca2+ sensitivity. We hypothesized that the putative internal troponin T-binding domain (amino acids 175-190) of β-TM may be responsible for the increased myofilament Ca2+ sensitivity observed when the entire β-TM is expressed in the heart. To test this hypothesis, we generated transgenic mice that expressed chimeric TM containing β-TM amino acids 175-190 in the backbone of α-TM (amino acids 1-174 and 191-284). These mice expressed 16-57% chimeric TM and did not develop cardiac hypertrophy or any other morphological changes. Physiological analysis showed that these hearts exhibited decreased rates of contraction and relaxation and a positive response to isoproterenol. Skinned fiber bundle analyses showed a significant increase in myofilament Ca2+ sensitivity. Biophysical experiments demonstrated that the exchanged amino acids did not influence the flexibility of the TM. This is the first study to demonstrate that a specific domain within TM can increase the Ca2+ sensitivity of the thin filament and affect sarcomeric performance. Furthermore, these results enhance the understanding of why TM mutations associated with familial hypertrophic cardiomyopathy demonstrate increased myofilament sensitivity to Ca2+.

Original languageEnglish (US)
Pages (from-to)H181-H190
JournalAmerican Journal of Physiology - Heart and Circulatory Physiology
Issue number1
StatePublished - Jul 2009


  • Calcium sensitivity
  • Contractile function
  • Genetically altered mice

ASJC Scopus subject areas

  • Physiology
  • Cardiology and Cardiovascular Medicine
  • Physiology (medical)


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