© 2003 by European Society of Cardiology
Copyright © 2003, European Society of Cardiology
The effect of myosin light chain 2 dephosphorylation on Ca2+-sensitivity of force is enhanced in failing human hearts
aLaboratory for Physiology, Institute for Cardiovascular Research (ICaR-VU), VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands
bUDMHSC Department of Cardiology, Debrecen, Hungary
cThorax Center, Erasmus University, Rotterdam, The Netherlands
dDepartment of Cardiology and Pneumology, Georg-August-University Goettingen, Goettingen, Germany
* Corresponding author. Tel.: +31-20-444-8121; fax: +31-20-444-8255 j.van_der_velden.physiol{at}med.vu.nl
Objective: Phosphorylation of the myosin light chain 2 (MLC-2) isoform expressed as a percentage of total MLC-2 was decreased in failing (21.1±2.0%) compared to donor (31.9±4.8%) hearts. To assess the functional implications of this change, we compared the effects of MLC-2 dephosphorylation on force development in failing and non-failing (donor) human hearts. Methods: Cooperative effects in isometric force and rate of force redevelopment (Ktr) were studied in single Triton-skinned human cardiomyocytes at various [Ca2+] before and after protein phosphatase-1 (PP-1) incubation. Results: Maximum force and Ktr values did not differ between failing and donor hearts, but Ca2+-sensitivity of force (pCa50) was significantly higher in failing myocardium (
pCa50=0.17). Ktr decreased with decreasing [Ca2+], although this decrease was less in failing than in donor hearts. Incubation of the myocytes with PP-1 (0.5 U/ml; 60 min) decreased pCa50 to a larger extent in failing (0.20 pCa units) than in donor cardiomyocytes (0.10 pCa units). A decrease in absolute Ktr values was found after PP-1 in failing and donor myocytes, while the shape of the Ktr–Ca2+ relationships remained unaltered. Conclusions: Surprisingly, the contractile response to MLC-2 dephosphorylation is enhanced in failing hearts, despite the reduced level of basal MLC-2 phosphorylation. The enhanced response to MLC-2 dephosphorylation in failing myocytes might result from differences in basal phosphorylation of other thin and thick filament proteins between donor and failing hearts. Regulation of Ca2+-sensitivity via MLC-2 phosphorylation may be a potential compensatory mechanism to reverse the detrimental effects of increased Ca2+-sensitivity and impaired Ca2+-handling on diastolic function in human heart failure.
KEYWORDS Cardiomyopathy; Contractile apparatus; Contractile function; Myocytes; Signal transduction
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