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Troponin I protein kinase C phosphorylation sites and ventricular function
Guy A MacGowan1, Caroline Evans, Tom C-C Hu
1Cardiovascular Institute, University of Pittsburgh, Pittsburgh, PA 15261, USA.
Cardiovascular Research
|July 14, 2004
Summary
Protein kinase C (PKC) phosphorylation of cardiac troponin I (cTnI) regulates cardiac muscle contraction. This study found that altering cTnI in transgenic (TG) mice amplified calcium-dependent contractility, revealing cTnI’s role in moderating heart muscle responses.
Area of Science:
- Cardiovascular Physiology
- Molecular Cardiology
- Biochemistry
Background:
- Protein kinase C (PKC) phosphorylation of cardiac troponin I (cTnI) reduces actomyosin ATPase activity.
- This effect is calcium-dependent and impacts active force development in cardiac muscle.
Purpose of the Study:
- To investigate the role of cTnI phosphorylation in cardiac function.
- To compare ventricular function in wild-type (WT) and cTnI transgenic (TG) mice lacking PKC phosphorylation sites.
Main Methods:
- Isolated perfused hearts studied for left ventricular function and mechanical restitution across varying calcium (Ca2+) levels.
- Manganese-enhanced MRI used to assess in-vivo sarcolemmal Ca2+ influx.
- Western blot analysis performed to determine cTnI phosphorylation status.
Main Results:
- Transgenic mice showed significantly greater ventricular contractility at high Ca2+ (3.5 mM).
- Reduced sarcolemmal Ca2+ influx was observed in TG mice via MRI.
- Increased cTnI phosphorylation was confirmed in TG mice by western blot.
Conclusions:
- Transgenic mice exhibit calcium-dependent positive inotropy without altered relaxation, suggesting compensatory mechanisms.
- PKC phosphorylation sites on cTnI attenuate contractile responses to intracellular Ca2+ changes.
- The study highlights cTnI's crucial role in modulating cardiac contractility.