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

Published on: August 1, 2016

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CaMKII and at least two unidentified kinases phosphorylate regulatory light chain in non-contracting cardiomyocytes

Hilde Eikemo1, Lise Román Moltzau1, Cam H T Nguyen1

  • 1Department of Pharmacology, Institute of Clinical Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway; Center for Heart Failure Research, Faculty of Medicine, University of Oslo and Oslo University Hospital, Oslo, Norway.

Biochemical and Biophysical Research Communications
|May 31, 2016
PubMed

Insights

Basal phosphorylation of myosin light chain 2 in cardiac cells involves multiple kinases, not just MLCK. CaMKII and other calcium-dependent and independent kinases ensure regulatory light chain phosphorylation through redundant activities.

Area of Science:

  • Cardiology
  • Molecular Biology
  • Biochemistry

Background:

  • Phosphorylation of regulatory light chain (RLC) in cardiac tissue modulates muscle contraction via Ca(2+)-sensitization.
  • Understanding the kinases responsible for basal RLC phosphorylation during diastole is crucial for cardiac function insights.

Purpose of the Study:

  • To identify the specific kinases involved in basal RLC phosphorylation in non-contracting adult rat cardiomyocytes.
  • To investigate the roles of Ca(2+)/calmodulin-dependent and independent kinases in RLC phosphorylation.

Main Methods:

  • Adult rat cardiomyocytes were studied in a non-contracting state.
  • Myosin light chain phosphatase (MLCP) was inhibited with calyculin A to reveal kinase activities.
  • Various protein kinase inhibitors, including KN-93 (CaMKII inhibitor) and staurosporine, were used.
  • Calmodulin antagonism (W7) and calcium reduction (EGTA) were employed.

Main Results:

  • Myosin light chain kinase (MLCK) was found not to contribute to RLC phosphorylation in non-contracting cardiomyocytes.
  • Two distinct kinase activity groups were identified based on staurosporine sensitivity.
  • CaMKII inhibition (KN-93) reduced RLC phosphorylation by 23% ± 7%.
  • Combined calmodulin antagonism and calcium reduction with staurosporine caused a greater decrease in RLC phosphorylation than staurosporine alone.

Conclusions:

  • Basal RLC phosphorylation in cardiac cells is mediated by redundant kinase activities.
  • Ca(2+)/calmodulin-dependent kinase II (CaMKII), another Ca(2+)/calmodulin-dependent kinase, and a Ca(2+)/calmodulin-independent kinase are involved.
  • These findings highlight a complex regulatory network ensuring RLC phosphorylation in cardiac tissue.
Keywords:
Ca(2+)/calmodulin-dependent kinase IIMyosin light chain kinaseMyosin light chain phosphatasePhosphorylationRegulatory light chain (RLC, myosin light chain 2)

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