Left ventricular and myocardial function in mice expressing constitutively pseudophosphorylated cardiac troponin I.
BACKGROUND
Protein kinase (PK)C-induced phosphorylation of cardiac troponin (cTn)I has been shown to regulate cardiac contraction.


OBJECTIVE
Characterize functional effects of increased PKC-induced cTnI phosphorylation and identify underlying mechanisms using a transgenic mouse model (cTnI(PKC-P)) expressing mutant cTnI (S43E, S45E, T144E).


RESULTS
Two-dimensional gel analysis showed 7.2+/-0.5% replacement of endogenous cTnI with the mutant form. Experiments included: mechanical measurements (perfused isolated hearts, isolated papillary muscles, and skinned fiber preparations), biochemical and molecular biological measurements, and a mathematical model-based analysis for integrative interpretation. Compared to wild-type mice, cTnI(PKC-P) mice exhibited negative inotropy in isolated hearts (14% decrease in peak developed pressure), papillary muscles (53% decrease in maximum developed force), and skinned fibers (14% decrease in maximally activated force, F(max)). Additionally, cTnI(PKC-P) mice exhibited slowed relaxation in both isolated hearts and intact papillary muscles. The cTnI(PKC-P) mice showed no differences in calcium sensitivity, cooperativity, steady-state force-MgATPase relationship, calcium transient (amplitude and relaxation), or baseline phosphorylation of other myofilamental proteins. The model-based analysis revealed that experimental observations in cTnI(PKC-P) mice could be reproduced by 2 simultaneous perturbations: a decrease in the rate of cross-bridge formation and an increase in calcium-independent persistence of the myofilament active state.


CONCLUSIONS
A modest increase in PKC-induced cTnI phosphorylation ( approximately 7%) can significantly alter cardiac muscle contraction: negative inotropy via decreased cross-bridge formation and negative lusitropy via persistence of myofilament active state. Based on our data and data from the literature we speculate that effects of PKC-mediated cTnI phosphorylation are site-specific (S43/S45 versus T144).
Kirk
Jonathan A
JA
Cardiovascular Systems Laboratory, Department of Bioengineering, University of Pittsburgh, Pittsburgh, PA 15219, USA.
MacGowan
Guy A
GA
Evans
Caroline
C
Smith
Stephen H
SH
Warren
Chad M
CM
Mamidi
Ranganath
R
Chandra
Murali
M
Stewart
Alexandre F R
AF
Solaro
R John
RJ
Shroff
Sanjeev G
SG
D008841:Actin Cytoskeleton / Q000201:enzymology; D000818:Animals; D020013:Calcium Signaling; D015180:Electrophoresis, Gel, Two-Dimensional; D051379:Mice; D008822:Mice, Transgenic; D008955:Models, Cardiovascular; D053580:Muscle Strength; D009154:Mutation; D009200:Myocardial Contraction / Q000235:genetics; D009206:Myocardium / Q000201:enzymology*; D010210:Papillary Muscles / Q000201:enzymology; D010766:Phosphorylation; D011493:Protein Kinase C / Q000378:metabolism*; D019210:Troponin I / Q000235:genetics / Q000378:metabolism*; D016277:Ventricular Function, Left / Q000235:genetics; D017725:Ventricular Pressure
D019210:Troponin I; D011493:Protein Kinase C