The effect of myosin light chain 2 dephosphorylation on Ca2+ -sensitivity of force is enhanced in failing human hearts.
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 (K(tr)) were studied in single Triton-skinned human cardiomyocytes at various [Ca(2+)] before and after protein phosphatase-1 (PP-1) incubation.


RESULTS
Maximum force and K(tr) values did not differ between failing and donor hearts, but Ca(2+)-sensitivity of force (pCa(50)) was significantly higher in failing myocardium (Deltap Ca(50)=0.17). K(tr) decreased with decreasing [Ca(2+)], 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 pCa(50) to a larger extent in failing (0.20 pCa units) than in donor cardiomyocytes (0.10 pCa units). A decrease in absolute K(tr) values was found after PP-1 in failing and donor myocytes, while the shape of the K(tr)-Ca(2+) 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 Ca(2+)-sensitivity via MLC-2 phosphorylation may be a potential compensatory mechanism to reverse the detrimental effects of increased Ca(2+)-sensitivity and impaired Ca(2+)-handling on diastolic function in human heart failure.
van der Velden
J
J
Laboratory for Physiology, Institute for Cardiovascular Research (ICaR-VU), VU University Medical Center, van der Boechorststraat 7, 1081 BT Amsterdam, The Netherlands. j.van_der_velden.physiol@med.vu.nl
Papp
Z
Z
Boontje
N M
NM
Zaremba
R
R
de Jong
J W
JW
Janssen
P M L
PM
Hasenfuss
G
G
Stienen
G J M
GJ
D000328:Adult; D002118:Calcium / Q000494:pharmacology / Q000502:physiology*; D024722:Cardiac Myosins / Q000378:metabolism* / Q000502:physiology; D002478:Cells, Cultured; D015180:Electrophoresis, Gel, Two-Dimensional; D005260:Female; D006333:Heart Failure / Q000378:metabolism* / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D009200:Myocardial Contraction / Q000187:drug effects / Q000502:physiology; D032383:Myocytes, Cardiac / Q000378:metabolism* / Q000502:physiology; D018994:Myosin Light Chains / Q000378:metabolism* / Q000502:physiology; D010749:Phosphoprotein Phosphatases / Q000494:pharmacology; D010766:Phosphorylation; D054645:Protein Phosphatase 1
D018994:Myosin Light Chains; C107184:myosin light chain 2; D010749:Phosphoprotein Phosphatases; D054645:Protein Phosphatase 1; D024722:Cardiac Myosins; D002118:Calcium