Increased cross-bridge cycling kinetics after exchange of C-terminal truncated troponin I in skinned rat cardiac muscle.
The precise mechanism of cardiac troponin I (cTnI) proteolysis in myocardial stunning is not fully understood. Accordingly, we determined the effect of cTnI C terminus truncation on chemo-mechanical transduction in isolated skinned rat trabeculae. Recombinant troponin complex (cTn), containing either mouse cTnI-(1-193) or human cTnI-(1-192) was exchanged into skinned cardiac trabeculae; Western blot analysis confirmed that 60-70% of the endogenous cTn was replaced by recombinant Tn. Incorporation of truncated cTnI induced significant reductions ( approximately 50%) in maximum force and cooperative activation as well as increases ( approximately 50%) in myofilament Ca(2+) sensitivity and tension cost. Similar results were obtained with either mouse or human truncated cTn. Presence of truncated cTnI increased maximum actin-activated S1 ATPase activity as well as its Ca(2+) sensitivity in vitro. Partial exchange (50%) for truncated cTnI resulted in similar reductions in maximum force and cooperativity; tension cost was increased in proportion to truncated cTnI content. In vitro, to determine the molecular mechanism responsible for the enhanced myofilament Ca(2+) sensitivity, we measured Ca(2+) binding to cTn as reported using a fluorescent probe. Incorporation of truncated cTnI did not affect Ca(2+) binding affinity to cTn alone. However, when cTn was incorporated into thin filaments, cTnI truncation induced a significant increase in Ca(2+) binding affinity to cTn. We conclude that cTnI truncation induces depressed myofilament function. Decreased cardiac function after ischemia/reperfusion injury may directly result, in part, from proteolytic degradation of cTnI, resulting in alterations in cross-bridge cycling kinetics.
Tachampa
Kittipong
K
Center for Cardiovascular Research and Department of Physiology and Biophysics, University of Illinois, Chicago, IL 60612, USA.
Kobayashi
Tomoyoshi
T
Wang
Helen
H
Martin
Anne F
AF
Biesiadecki
Brandon J
BJ
Solaro
R John
RJ
de Tombe
Pieter P
PP
D008841:Actin Cytoskeleton / Q000378:metabolism / Q000473:pathology; D000818:Animals; D002118:Calcium / Q000378:metabolism; D006801:Humans; D007700:Kinetics; D008297:Male; D040542:Mechanotransduction, Cellular / Q000187:drug effects; D015428:Myocardial Reperfusion Injury / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D017682:Myocardial Stunning / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D009206:Myocardium / Q000378:metabolism* / Q000473:pathology; D009218:Myosins / Q000378:metabolism; D051381:Rats; D011917:Rats, Inbred Lew; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism / Q000494:pharmacology; D019210:Troponin I / Q000235:genetics / Q000378:metabolism* / Q000494:pharmacology
D011994:Recombinant Proteins; D019210:Troponin I; D009218:Myosins; D002118:Calcium