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Updated: May 12, 2026

Assessment of Myofilament Ca2+ Sensitivity Underlying Cardiac Excitation-contraction Coupling
08:29

Assessment of Myofilament Ca2+ Sensitivity Underlying Cardiac Excitation-contraction Coupling

Published on: August 1, 2016

Familial dilated cardiomyopathy mutations uncouple troponin I phosphorylation from changes in myofibrillar Ca²⁺

Massimiliano Memo1, Man-Ching Leung, Douglas G Ward

  • 1Myocardial Function, NHLI, Imperial College London, London, W12 0NN, UK.

Cardiovascular Research
|March 30, 2013
PubMed
Abstract

Insights

Familial dilated cardiomyopathy (DCM) mutations in thin filament proteins disrupt the normal response to protein kinase A (PKA) phosphorylation. This uncoupling may impair the heart's ability to respond to stress, contributing to DCM development.

Area of Science:

  • Cardiology
  • Molecular Biology
  • Biochemistry

Background:

  • Familial dilated cardiomyopathy (DCM) is often caused by mutations in sarcomeric protein genes.
  • Previous studies suggested DCM mutations decrease myofibrillar Ca(2+) sensitivity, but findings were inconsistent.

Purpose of the Study:

  • To re-investigate the molecular mechanisms of familial DCM using native proteins.
  • To clarify the impact of DCM mutations in thin filament proteins on myofilament Ca(2+) sensitivity and its regulation.

Main Methods:

  • Quantitative in vitro motility assay using native troponin and tropomyosin.
  • Analysis of DCM mutations in troponin I, troponin T, and α-tropomyosin.
  • Assessment of protein kinase A (PKA) phosphorylation effects on myofilament Ca(2+) sensitivity.

Main Results:

  • Four DCM mutations reduced myofilament Ca(2+) sensitivity; one (TPM1 E54K) had no effect, and another (TPM1 D230N) increased it.
  • PKA phosphorylation of troponin I decreased Ca(2+) sensitivity in normal filaments but had no effect in DCM-mutant filaments ('uncoupling').
  • This uncoupling was observed with native and recombinant mutant proteins and was independent of mutation fraction above 0.55.

Conclusions:

  • DCM-causing mutations in thin filament proteins abolish the link between myofilament Ca(2+) sensitivity and PKA phosphorylation.
  • This disruption likely blunts the heart's response to β-adrenergic stimulation, potentially causing long-term DCM.
Keywords:
Ca2+ regulation of contractilityFamilial dilated cardiomyopathyIn vitro motility assayMutationsTroponin phosphorylation

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