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Assessment of Myofilament Ca2+ Sensitivity Underlying Cardiac Excitation-contraction Coupling
Published on: August 1, 2016
Changes in cyclic nucleotide phosphodiesterase activity and calmodulin concentration in heart muscle of
Rumi Masunaga1, Akio Nagasaka, Yoshikuni Sawai
1Department of Internal Medicine, Fujita Health University School of Medicine, Toyoake, Aichi 470 1192, Japan.
Insights
Calmodulin (CaM) levels and cyclic nucleotide phosphodiesterase (PDE) isozyme activities change in cardiomyopathic hamster hearts. These alterations in CaM and PDE may affect cardiac contractility by modifying cyclic nucleotide levels.
Area of Science:
- Cardiovascular Science
- Biochemistry
- Molecular Biology
Background:
- Cyclic nucleotide phosphodiesterase (PDE) activity and expression are altered in cardiomyopathic heart failure.
- PDE inhibitors can improve cardiac muscle function by altering cyclic nucleotide concentrations.
- Calmodulin (CaM) is a potential regulator of cyclic nucleotide PDE activities.
Purpose of the Study:
- To investigate the role of calmodulin (CaM) in regulating cyclic nucleotide PDE activities.
- To study the modulation of PDE isozymes in heart failure using cardiomyopathic hamster cardiac muscle.
Main Methods:
- Measurement of CaM concentrations in heart muscle fractions from control and cardiomyopathic hamsters of varying ages.
- Solubilization and isolation of PDE isozymes (PDE I, II, and III) from hamster heart muscle using DEAE-cellulose chromatography.
- Assay of PDE activities and determination of CaM inhibitor W-7's IC(50) for different PDE isozymes.
Main Results:
- CaM concentrations in the soluble fraction of cardiomyopathic hamster hearts significantly increased with age (25 and 32 weeks) compared to controls.
- Solubilized PDE activity, particularly peak III (likely PDE III), declined with age in cardiomyopathic hamster hearts compared to controls.
- PDE II was found to be more sensitive to the CaM inhibitor W-7 (IC(50) = 29 microM) compared to PDE I (140 microM) and PDE III (46 microM).
Conclusions:
- Alterations in CaM concentration and PDE isozyme activities occur in the failing hearts of cardiomyopathic hamsters.
- These changes may influence cardiac muscle contractility through modifications in cyclic nucleotide signaling pathways.
- PDE II's sensitivity to CaM inhibition suggests a specific regulatory role for CaM in this isozyme.
Abstract:
Cyclic nucleotides (cAMP and cGMP) phosphodiesterase (PDE) activities and expression are altered in the cardiac muscle of cardiomyopathic heart failure, and PDE inhibitors improve the abnormal muscle condition through changing the cyclic nucleotide concentration. These observations prompted us to investigate the role of calmodulin (CaM) in the regulation of cyclic nucleotide PDE activities, and moreover to study the modulation of the PDE isozymes in heart failure, using cardiac muscles of cardiomyopathic hamster. The CaM concentrations in the heart muscle of the normal control and cardiomyopathic hamsters (each of three to four hamsters) varied with cell fraction and with the age of the animal. The CaM concentrations in the soluble fraction obtained from cardiomyopathic hamster tissue were significantly increased at 25 and 32 weeks of age (2.02 +/- 0.62 microg/mg protein (mean +/- S.E.), and 3.21 +/- 0.95) compared with that obtained from the control (0.60 +/- 0.04) or cardiomyopathic (0.95 +/- 0.12) hamsters at 8 weeks of age. The solubilized PDE isolated from the hamster heart muscle (three or four hamsters in each age) by column chromatography on diethylaminoethyl (DEAE)-cellulose revealed three peaks of activity, which may correspond to the isozymes of PDE classified recently, namely PDE I, II, and III. These three peaks of activity, particularly peak III, seen in the soluble fraction of cardiomyopathic hamster heart declined in proportion to the age of the animal compared with that of the control hamster heart. In the cGMP-PDE assay system, the concentration of CaM inhibitor W-7 required for 50% inhibition (IC(50)) of PDE I, II, and III peak activities was 140, 29, and 46 microM, respectively, suggesting that PDE II is more sensitive to W-7. These results suggest that alteration in these isozyme activities accompanied with changes of CaM concentration may influence the cardiac muscle contractility in cardiomyopathic hamster via changes of cyclic nucleotide concentration.
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