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J. Biol. Chem., Vol. 276, Issue 19, 15753-15760, May 11, 2001
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From the In a tail suspension rat model, we investigated
changes in myofilament protein during cardiac adaptation in simulated
microgravity. Contractile force and velocity of cardiac muscle were
decreased in the tail suspension rats as compared with the control.
Ca2+-dependent actomyosin ATPase activity
was also decreased; however, sensitivity of cardiac muscle to
Ca2+ activation was unchanged. There was no change in
expression of myosin heavy chain, tropomyosin, troponin T, or troponin
I isoforms in hearts of tail suspension rats. A novel finding is a
fragment of cardiac troponin I (cTnI) that had increased amounts in the heart of tail suspension rats. Binding of this cTnI fragment by a
monoclonal antibody that specifically recognizes the COOH terminus indicates an intact COOH terminus. NH2-terminal sequence
analysis of the cTnI fragment revealed truncations primarily of amino
acids 1-26 and 1-27 and smaller amounts of 1-30, including
Ser23 and Ser24, which are substrates of
protein kinase A phosphorylation. This cTnI fragment is present in
normal cardiac muscle and incorporated into myofibrils, indicating a
role in regulating contractility. This proteolytic modification of cTnI
up-regulated during simulated microgravity suggests a potential role of
the NH2-terminal segment of cTnI in functional adaptations
of cardiac muscle.
A Proteolytic NH2-terminal Truncation of Cardiac
Troponin I That Is Up-regulated in Simulated Microgravity*
§,¶
Department of Physiology and Biophysics,
Case Western Reserve University School of Medicine, Cleveland, Ohio
44106-4970 and the § Department of Aerospace Physiology, The
Fourth Military Medical University, Xi'an, China 710032
*
This work was supported in part by a grant from the
March of Dimes Foundation (to J.-P. J.) and a National Natural Science Foundation of China Grant 39670800 (to L.-F. Z.).The costs of publication of this
article were defrayed in part by the
payment of page charges. The article
must therefore be hereby marked
"advertisement" in
accordance with 18 U.S.C. Section
1734 solely to indicate this fact.
Copyright © 2001 by The American Society for Biochemistry and Molecular Biology, Inc.
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