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Contractile effects of the exchange of cardiac troponin for fast skeletal troponin in rabbit psoas single myofibrils
Author(s) -
Piroddi N.,
Tesi C.,
Pellegrino M. A.,
Tobacman L. S.,
Homsher E.,
Poggesi C.
Publication year - 2003
Publication title -
the journal of physiology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.802
H-Index - 240
eISSN - 1469-7793
pISSN - 0022-3751
DOI - 10.1113/jphysiol.2003.051615
Subject(s) - myofibril , troponin , isometric exercise , chemistry , troponin c , biophysics , troponin i , troponin t , skeletal muscle , myosin , crossbridge , myofilament , actin , troponin complex , biochemistry , medicine , anatomy , biology , myocardial infarction
The effects of the removal of fast skeletal troponin C (fsTnC) and its replacement by cardiac troponin C (cTnC) and the exchange of fast skeletal troponin (fsTn) for cardiac troponin (cTn) were measured in rabbit fast skeletal myofibrils. Electrophoretic analysis of myofibril suspensions indicated that replacement of fsTnC or exchange of fsTn with cTnC or cTn was about 90% complete in the protocols used. Mechanical measurements in single myofibrils, which were maximally activated by fast solution switching, showed that replacement of fsTnC with cTnC reduced the isometric tension, the rate of tension rise following a step increase in Ca 2+ ( k act ), and the rate of tension redevelopment following a quick release and restretch ( k tr ), but had no effect on the kinetics of the fall in tension when the concentration of inorganic phosphate (P i ) was abruptly increased ( k Pi(+) ). These data suggest that the chimeric protein produced by cTnC replacement in fsTn alters those steps controlling the weak‐to‐strong crossbridge attachment transition. Inefficient signalling within the chimeric troponin may cause these changes. However, replacement of fsTn by cTn had no effect on maximal isometric tension, k act or k tr , suggesting that these mechanics are largely determined by the isoform of the myosin molecule. Replacement of fsTn by cTn, on the other hand, shifted the pCa 50 of the pCa‐tension relationship from 5.70 to 6.44 and reduced the Hill coefficient from 3.3 to 1.4, suggesting that regulatory protein isoforms primarily alter Ca 2+ sensitivity and the cooperativity of the force‐generating mechanism.