Charged residue alterations in the inner-core domain and carboxy-terminus of α-tropomyosin differentially affect mouse cardiac muscle contractility

Autor: Mariappan Muthuchamy, David C. Zawieja, Jeffrey Robbins, Robert D. Gaffin, Raisa Klevitsky, Carl W. Tong, Timothy E. Hewett
Rok vydání: 2004
Předmět:
Zdroj: The Journal of Physiology. 561:777-791
ISSN: 0022-3751
Popis: Two important charge differences between the α- and β-tropomyosin (TM) isoforms are the exchange of a serine residue in the inner-core region at position 229, and a histidine residue at the carboxy-terminal end at position 276, with glutamic acid and asparagine, respectively. We have recently shown that altering these two residues in α-TM to their β-TM counterparts in transgenic (TG) mouse hearts causes a depression in both +dP/dt and −dP/dt and a decrease in calcium sensitivity. In this study, we address whether independent charge changes at these two residues in α-TM modulate cardiac function differentially. To test this hypothesis we generated two TG lines: α-TMSer229Glu and α-TMHis276Asn. Molecular analyses show that 98% of native α-TM is replaced by mutated protein in α-TM229 hearts whereas α-TM276 hearts show 82% replacement with the mutated protein. Isolated working heart data show that α-TM229 TG hearts exhibit a significant decrease in both +dP/dt (7%) and −dP/dt (8%) compared with nontransgenics (NTGs) and time to peak pressure (TPP) is also reduced in α-TM229 hearts. α-TM276 hearts show a decrease only in −dP/dt (14%) and TPP is increased. pCa2+–tension relationships in skinned fibre preparations indicate decreased calcium sensitivity in α-TM229 but no change in α-TM276 preparations. Force–[Ca2+]IC measurements from intact papillary fibres indicate that α-TM276 fibres produce more force per given [Ca2+]IC when compared to NTG fibres, while α-TM229 fibres produce less force per given [Ca2+]IC. These data demonstrate that changing charged residues at either the inner-core domain or the carboxyl end of TM alters sarcomeric performance differently, suggesting that the function of TM is compartmentalized along its length.
Databáze: OpenAIRE
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