Troponin C isoform composition determines differences in Sr2+-activation characteristics between rat diaphragm fibers

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O'Connell, Brett, Stephenson, D. George, Blazev, Ronnie and Stephenson, Gabriela (2004) Troponin C isoform composition determines differences in Sr2+-activation characteristics between rat diaphragm fibers. The American journal of physiology - cell physiology, 287 (1). C79-C87. ISSN 1522-1563 Online 0363-6143 Print

Abstract

Troponin C isoform composition determines differences in Sr2+ -activation characteristics between rat diaphragm fibers. Am J Physiol Cell Physiol 287: C79–C87, 2004. First published February 25, 2004; 10.1152/ajpcell.00555.2003.— Single fibers of rat diaphragm containing different naturally occurring combinations of myofibrillar protein isoforms were used to evaluate the contribution of troponin C (TnC) isoforms to fiber type-related differences with respect to sensitivity to Sr2+ of the contractile system. Mechanically skinned fibers were studied for their isometric force vs. Sr2+ concentration ([Sr2+]) relationships and then analyzed electrophoretically for myofibrillar protein isoform composition. Our data demonstrate that fiber-type differences in Sr2+ dependence of contractile activation processes are primarily determined by the TnC isoform composition, with the slow isoform conferring on average a sevenfold greater sensitivity to Sr2+ than the fast isoform. Moreover, the ratio of TnC isoforms determined functionally from the force-pSr (+log10 [Sr2+]) curves is tightly (r2 + 0.97) positively correlated with that estimated electrophoretically. Together, these results validate the use of Sr2+ activation characteristics to distinguish fibers containing different proportions of fast and slow TnC isoforms and to study the mechanisms by which divalent cations activate the contractile apparatus. We also found that the functionally and electrophoretically determined ratios of TnC isoforms present in a fiber display similar sigmoidal relationships with the ratio of myosin heavy chain (MHC) isoform types expressed. These relationships 1) offer further insight in the functional and molecular expression of TnC in relation to the molecular expression of MHC isoform types and 2) may provide the basis for predicting sensitivity to Sr2+, TnC, and MHC isoforms in pure and hybrid skeletal muscle fibers.

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Item type Article
URI https://vuir.vu.edu.au/id/eprint/1051
DOI https://doi.org/10.1152/ajpcell.00555.2003
Official URL http://ajpcell.physiology.org/cgi/reprint/287/1/C7...
Funders http://purl.org/au-research/grants/nhmrc/256602
Subjects Historical > RFCD Classification > 210000 Science-General
Historical > Faculty/School/Research Centre/Department > School of Biomedical and Health Sciences
Keywords muscle contraction, skeletal muscle, myofibrillar proteins, single fiber, sensitivity to strontium, sensitivity to calcium
Citations in Scopus 16 - View on Scopus
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