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Updated: Oct 1, 2026

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice
06:22

Contractility Measurements on Isolated Papillary Muscles for the Investigation of Cardiac Inotropy in Mice

Published on: September 17, 2015

alpha-Adrenergic response and myofilament activity in mouse hearts lacking PKC phosphorylation sites on cardiac TnI

David E Montgomery1, Beata M Wolska, W Glen Pyle

  • 1Program in Cardiovascular Sciences, Department of Physiology and Biophysics, Section of Cardiology, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA.

American Journal of Physiology. Heart and Circulatory Physiology
|May 11, 2002
PubMed

Insights

Protein kinase C (PKC) phosphorylation of cardiac troponin I (cTnI) at Ser43/45 depresses heart muscle force. This study shows that blocking these sites reduces force depression, highlighting their role in heart failure.

Area of Science:

  • Cardiovascular Physiology
  • Molecular Cardiology
  • Biochemistry

Background:

  • Protein kinase C (PKC) phosphorylation of cardiac myofilament proteins can impair actomyosin interaction.
  • This PKC-mediated effect is implicated in the pathophysiology of heart failure.
  • Specific phosphorylation sites on cardiac troponin I (cTnI), Ser43 and Ser45, are key to this depression.

Purpose of the Study:

  • To investigate the role of specific PKC-dependent phosphorylation sites (Ser43 and Ser45) on cardiac troponin I (cTnI) in regulating cardiac muscle force.
  • To compare the effects of PKC activation on cardiac muscle force in nontransgenic (NTG) and transgenic (TG) mice with altered cTnI phosphorylation sites.

Main Methods:

  • Studied intact and detergent-extracted papillary muscles from NTG and TG mice expressing mutant cTnI (Ser43Ala, Ser45Ala).
  • Administered phenylephrine (PE) to intact muscles and phorbol ester to detergent-extracted fibers.
  • Utilized a PKC-specific inhibitor (chelerythrine) and measured cTnI and cardiac troponin T (cTnT) phosphorylation levels.

Main Results:

  • Phenylephrine treatment caused a transient increase and subsequent 62% force reduction in NTG muscles, versus no transient increase and a 45% reduction in TG muscles.
  • TG fibers showed reduced force depression compared to NTG fibers after phorbol ester treatment.
  • PKC inhibition with chelerythrine blocked these force-regulating responses, and cTnI phosphorylation correlated with force changes, alongside decreased cTnT phosphorylation in TG fibers.

Conclusions:

  • Specific PKC-mediated phosphorylation of Ser43 and Ser45 on cTnI is crucial for regulating force development in the intact myocardium.
  • These findings provide direct evidence for the functional significance of cTnI phosphorylation in cardiac contractility.
  • Targeting these specific phosphorylation sites may offer a therapeutic strategy for heart failure conditions characterized by impaired contractility.

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